What is the best way to build muscle ?

What are muscles ?

Did you know you have more than 600 muscles in your body ? These muscles help you move, lift things, pump blood through your body, and even help you breathe.

When you think about your muscles, you probably think most about the ones you can control. These are your voluntary muscles, which means you can control their movements. They are also called skeletal muscles, because they attach to your bones and work together with your bones to help you walk, run, pick up things, play an instrument, throw a baseball, kick a soccer ball, push a lawnmower, or ride a bicycle. The muscles of your mouth and throat even help you talk and eat.

Smooth muscles are also called involuntary muscles since you have no control over them. Smooth muscles work in your digestive system to move food along and push waste out of your body. They also help keep your eyes focused without your having to think about it.

Did you know your heart is also a muscle ? Cardiac muscle is a specialized type of involuntary muscle. It pumps blood through your body, changing its speed to keep up with the demands you put on it. It pumps more slowly when you’re sitting or lying down, and faster when you’re running or playing sports and your skeletal muscles need more blood to help them do their work.

Skeletal muscles are connected to your bones by tough cords of tissue called tendons. As the muscle contracts, it pulls on the tendon, which moves the bone. Bones are connected to other bones by ligaments, which are like tendons and help hold your skeleton together.

Skeletal muscle is a highly plastic tissue. The ability of adult muscle fibres to change in response to external stimuli has been called muscle plasticity. Force, contraction speed, endurance and oxidative/glycolytic capacity are all examples of muscle properties that are plastic ¹⁾. Skeletal muscle is a permanent, post-mitotic tissue, and unless the muscle is damaged there is little turnover of cells ²⁾, ³⁾. Thus, it has been demonstrated that dramatic changes in gene expression, protein composition and physiological properties can occur in pre-existing fibres without de- or regeneration ⁴⁾, ⁵⁾. The plastic changes occur mainly by reprogramming the cell by turning on and off sets of relevant genes.

Exercise evokes signaling pathways that strongly modify myofiber metabolism and physiological and contractile properties of skeletal muscle. Regular physical activity is beneficial for health and is highly recommended for the prevention of several chronic conditions ⁶⁾.

Muscle fibre phenotypes

Mammalian skeletal muscles are composed of myofibers with various contractile properties (such as force production, endurance, twitch duration, and shortening velocity) and differing metabolism. Myofibers are mainly classified as slow-twitch or fast-twitch based on the maximal speed of shortening ⁷⁾. In human muscle 3 fibre subtypes are recognized based on their contractile and metabolic properties ⁸⁾. Fast-twitch fatigable fibres rely predominantly on glycolytic metabolism and are designated FG (fast glycolytic), whereas, fast-twitch fatigue-resistant and slow-twitch fibres have relatively greater mitochondrial content and are designated FOG (fast oxidative glycolytic) and SO (slow oxidative), respectively ⁹⁾. The fibre type-specific differences in contractile function are due to differential expression of a diverse range of isoforms of each myofibrillar protein ¹⁰⁾. Myosin heavy chain (MyHC) isoforms are intimately associated with myofibre contractile and energetic properties and are commonly used molecular markers: FG fibres express MyHC IIx/d, FOG fibres express MyHC IIa and SO fibres express MyHC I, which is also the predominant isoform in adult human myocardium. Indeed, myosin ATPase activity determines the sliding velocity between actin and myosin, thereby shortening the velocity of the fiber ¹¹⁾. Myosin ATPase type I histochemical staining identifies slow-twitch fibers, while myosin ATPase type II (which has the highest ATPase activity) stains fast-twitch myofibers. Based on the expression of the predominant isoforms of MyHC protein expressed, myofibers are mainly classified as type I fibers, type IIx/d fibers, and type IIa fibers ¹²⁾, ¹³⁾ (Figure 1).

In addition to the three or four major MyHC genes expressed in adult limb muscles there are specialized forms expressed during development and in gill-arch-derived muscles. In total 10 different MyHC genes have been connected to skeletal muscle ¹⁴⁾.

While histochemical or immunohistochemical staining might give the impression that the vast majority of fibres are positive only for one MyHC, single-fibre gel electrophoresis has revealed that 11–67% of the fibres from various limb muscles express more than one MyHC isoform even under steady-state activity conditions ¹⁵⁾. It can be concluded that the concept of universal fibre types throughout the body is an oversimplification.

Figure 1. Characteristics of mammalian skeletal muscle fiber types. The red color is associated with a high content of myoglobin

[Source ¹⁶⁾]

Note: MyHC, myosin heavy-chain; SDH, succinate dehydrogenase; LDH, lactate dehydrogenase; CSA, cross-sectional area.

Type I fibers (slow-twitch fibers) contain the slow isoform of MyHC and slow isoforms of other contractile proteins. They have a predominatly oxidative metabolism. They are characterized by high mitochondrial content, high capillary density and express mainly glucose and fatty acid oxidative enzymes. Type I fibers are rich in myoglobin and are red colored. They develop a slow contractile force and are resistant to fatigue. They are involved in continuous tonic activity. Force production depends on the time the myosin head spends bound to actin, on the myosin head density and on the duty ratio ¹⁷⁾.

Type IIx/d fibers (fast-twitch fibers) express a fast isoform of MyHC and fast isoforms of other contractile proteins and, therefore, develop a fast contractile force. Type IIx/d fibers mainly metabolize glucose by glycolysis and are characterized by low mitochondrial content and low capillary density. They are also poor in myoglobin and are white in appearence. Type IIx/d fibers express low glucose transporter 4 (GLUT4) and have low sensitivity to insulin that type I fibers. They are involved in phasic activity ¹⁸⁾.

Type IIa fibers (fast-twitch fibers) have intermediate features. They have a mixed (oxidative/glycolytic) metabolism. They are fast-twitch fibers with a fast contractile force development, but mainly express oxidative enzymes. Although muscle endurance and resistance to fatigue rely on several cellular factors, there is a strict correlation between these properties and high oxidative capacity and high content of mitochondria of the fiber. Therefore, type IIa fibers are fast but they are more resistant to fatigue than type IIx/d fibers as they are more oxidative ¹⁹⁾, ²⁰⁾.

Rodents also possess type IIb fibers that are more fast-twich and glycolytic than IIx/d fibers (Fig. 1). Many other contractile and structural proteins are also present in distinct isoforms whose expression is more or less tightly connected to fiber type. For example, the shortening velocity also depends on myosin light chain isoforms; thus, it might vary among fibers of the same MyHC type. Therefore, the classification reported earlier in four main fiber types is an oversimplification. Moreover, muscle also contains hybrid fibers with a combination of myosin transcripts (I-IIa-IIx/d-IIb).

The velocity of shortening and the fiber’s twitch duration depend not only on myosin composition but also on the speed of Ca2+ release and uptake in the fiber. These, in turn, depend on the development of sarcoplasmic reticulum and on sequestering systems such as the sarcoplasmic reticulum Ca2+ ATPases (SERCAs) whose isoforms are differentially expressed in different fiber types ²¹⁾, ²²⁾.

Changes in muscle fibre phenotypes

The physiological properties (shortening velocity, twitch duration, endurance, etc.) that are linked in a fibre type are related to highly different molecular families (MyHC, SERCA, metabolic enzymes, etc.). Coupling regulation of different physiological properties may be beneficial from an energy conservation point of view, and/or it might reflect common signaling systems diverging to regulate several sets of diverse genes. To some extent however, different properties can be uncoupled and regulated independently during plastic changes. For example, some degree of uncoupling has been observed between twitch speed and shortening velocity ²³⁾. More importantly, endurance-exercise in man and in other animals can lead to pronounced changes in metabolic properties without MyHC fibre-type conversion ²⁴⁾, ²⁵⁾, ²⁶⁾, although exercise can also change MyHC type in particular within type II (e.g. from type IIb/IIx to IIa) ²⁷⁾, ²⁸⁾, ²⁹⁾ and under more severe experimental conditions fibre-type conversions are frequent.

When fibre-type conversions occur, it usually happens in a sequential order ³⁰⁾, ³¹⁾: I ↔ IIa ↔ IIx ↔ IIb. During transitions hybrids between the “nearest neighbour” fibre type in this flow chart (e.g. I+IIa, IIa+IIx) are common, but aberrant hybrids such as I+IIb, I+IIa+IIb and I+IIx+IIb can also be seen under some experimental conditions ³²⁾.

Determinants of muscle fibre phenotype

The factors that determine the molecular make-up of already formed adult muscles, and how that make-up can change. At any point in time, a fibre’s make-up appears to depend on previous: (1) cell history/lineage; (2) nerve-evoked electrical activity; (3) mechanical conditions; (4) para-/autocrine conditions; and (5) circulating hormones.

There is a consensus that changes in muscle usage will transform muscle phenotype, but the precise biological signaling mechanisms responsible for such changes are less clear.

Muscle properties are strongly influenced by hormones such as testosterone and thyroid hormones, as reviewed previously ³³⁾, ³⁴⁾, ³⁵⁾. The link between external factors related to activity and usage (points 2 and 3 above) and gene expression and the ability to change is, however, constrained by the muscle’s cell lineage.

The importance of cell lineage

Developmental studies suggest that initial fibre-type differentiation might be determined by myoblast cell lineage independent of external influences such as innervation or usage.

In adult rats, when different muscles are regenerating from myoblasts after myofibre destruction, the various regenerated muscles express different MyHC types reminiscent of the muscle of origin. This happens even if the muscles receive similar experimental patterns of activity. Thus, when regenerating soleus and extensor digitorum longus (EDL) were stimulated by the same slow pattern, the EDL failed to express the large amount of slow MyHC that was observed in the soleus under the same conditions ³⁶⁾.

While it seems clear that cell lineage limits the adaptive range of muscle plasticity, it is equally clear that external signals can change muscle phenotype in the adult. In particular signals from the nerve appear to be important.

It can be concluded that muscle fibre pedigree matters, and that there is a cell line component to the resulting adult phenotype of a fibre. The relationship is, however, not simple, since experiments with genetically marked myoblasts suggest that single myoblast clones can contribute to both fast and slow fibres, clones are not restricted to contribute to subsets of fibre types, and clones show no detectable preference for fusion to a particular fibre type ³⁷⁾.

What are the signals from the nerve ?

There is currently no compelling evidence to suggest that there are any relevant sources of neural influence on the muscle other than activity, and in spite of intense searching for several decades, no neurotrophic substances have been identified that prevent atrophy or mimic other effects of normal innervation or cross-innervation outside the synaptic zone ³⁸⁾.

The importance of nerve-evoked muscle activity

Generally type I motor units seem to receive high amounts of impulses delivered in long low-frequency trains, while type II units seem to receive short bursts of high-frequency activity. The total amount of impulses delivered to type II units is lower, but the amount seems to vary among the type II subtypes.

Mechanical stress

It is widely assumed that contraction against a resistance leads to larger muscles than contraction against lower resistance, but this does not necessarily have a direct bearing on the importance of mechanical factors as such.

The most compelling evidence for a mechano-dependent mechanism comes from experiments where limbs have been immobilized by a cast. This leads to atrophy, but studies over almost 100 years have shown that atrophy can be partly counteracted when muscles are immobilized in a lengthened position rather than a shortened position. There are also studies suggesting that muscle length influences contraction speed such that chronic stretch makes a muscle slower; immobilization of fast muscles in a lengthened position thus increases the fraction of slow fibres. In most experimental conditions it is hard to separate electrical activity and mechanical stretch, but some experimental data point to the presence of an activity-independent mechanical mechanism influencing muscle size and perhaps contraction speed.

Myostatin

Myostatin (previously called GDF-8) is a member of the transforming growth factor β (TGF-β) superfamily and plays a major role during development where it acts as an inhibitor of muscle growth. Disruption of the myostatin gene leads to development of grossly enlarged muscles in mice ³⁹⁾, farm animals ⁴⁰⁾, and man ⁴¹⁾. The enlargement is caused both by an increase in the number of fibres (hyperplasia) and in fibre size (hypertrophy). Importantly, muscle enlargement obtained by myostatin deficiency is peculiar because it does not increase force in proportion to size, thus the amount of contractile proteins may not be properly regulated ⁴²⁾, ⁴³⁾. Thus, reducing myostatin alone might not mimic effects of strength training, although strength training in adults has been shown to be associated with reduced levels of myostatin in muscle and plasma ⁴⁴⁾, ⁴⁵⁾. In adult animals inhibition of myostatin with antibodies leads to hypertrophy without an increase in the number of fibres ⁴⁶⁾; conversely, overexpression of myostatin in muscle fibres after electroporation leads to muscle atrophy without loss of muscle fibres ⁴⁷⁾. In the latter study it was suggested that myostatin acted by reducing muscle gene expression of myofibrillar proteins perhaps by reducing expression of MyoD and myogenin. In addition, myostatin might activate the ubiquitin-proteasome pathway for proteolysis ⁴⁸⁾.

Insulin-like growth factor I (IGF-1)

IGF-1 has been implicated as a factor promoting hypertrophy in the adult animal. The liver supplies approximately 75% of the circulating IGF-1 (Schwander et al., 1983), and a selective abolishment of IGF-1 production in hepatocytes leads to a 75% reduction in circulating IGF-1 levels but without growth impairment ⁴⁹⁾. In humans increasing the circulating level of IGF-1 does not promote muscle protein synthesis ⁵⁰⁾. IGF-1 is also expressed locally in several tissues including muscle where it is induced by stretch or high-resistance exercise. IGF-1 seems to work as a local hormone that promotes hypertrophy in adult muscle. It might do so both by interfering with protein balance in muscle fibres and by activating satellite cells, but for the latter there is still little information in adult muscles.

Figure 2. Muscles anatomy front

Figure 3. Muscles anatomy back

Figure 4. Muscle anatomy – simplified for bodybuilding and body builders

The cell biology of muscle fibre size

Regulation of force is mainly a question of regulating fibre size, and ultimately size is regulated by altering the balance between protein synthesis and degradation in each muscle fibre. Change in fibre size can be achieved by regulating three major conditions: (1) the number of nuclei; (2) the rate of protein synthesis for each nucleus; and (3) the rate of protein degradation.

Figure 5. Pathways currently believed to be involved in regulating muscle fibre size

[Source ⁵¹⁾]

The pathways have different degrees of scientific support, and their relative importance is still poorly understood. Abbreviations: forkhead box O (FoxO), glycogen synthase kinase 3 (GSK3), inhibition-of-DNA-binding-protein 1 (Id-1), insulin-like growth factor I (IGF-1), mammalian target of rapamycin (mTOR), myogenic regulatory factor (MRF), phosphatidylinositol 3-kinases/Akt (PI(3)K/Akt), serum response factor (SRF), κ light polypeptide gene enhancer in B-cells (NFκB).

Metabolic pathways for ATP production in skeletal myofibers

Metabolic pathways for ATP production in skeletal myofibers. (A) Skeletal muscles require a high amount of ATP for contraction. The main sources of energy are Glu and FFA. Glu uptake into the sarcoplasm from blood occurs, among other things, through the GLUT4. Once in the cytosol, Glu is phosphorylated by HK and forms Glu-6-P. One molecule of Glu-6-P can be converted into two molecules of Pyr through glycolysis, a metabolic anaerobic pathway involving 10 enzymes (the enzyme phosphofructokinase is an important control point in the glycolytic pathway). Depending on the energy needs, Glu-6-P can also be stored as glycogen. In anaerobic conditions Pyr is reduced to lactate by LDH. Alternatively, in aerobic conditions, Pyr might be transferred into the mitochondria matrix, where it is decarboxylated into acetyl-CoA by the PDH complex. Acetyl-CoA is then metabolized through the TCA cycle. The first enzyme acting in the TCA cycle is the citrate synthase that forms citrate from acetyl-CoA and oxaloacetate. The TCA cycle produces reducing equivalents (NADH, FADH2) and CO2. In addition to Pyr, another important source of acetyl-CoA is the β-oxidation of FFA. FFA enter the myofiber through a passive flip-flop or through a protein-mediated mechanism such as the FAT/CD36. In the cytosol, FFA undergo esterification and form triglycerides stored as lipid droplets that are surrounded by mitochondria. Alternatively, at the mitochondrial OM, they can be condensed with CoA to form FFA-CoA and, through the CPT1, they can cross the mitochondrial IM and reach the mitochondrial matrix where they undergo β-oxidation. β-oxidation is a cycle of four reactions. Each cycle produces a molecule of acetyl-CoA which, in turn, enters the TCA cycle. Along with acetyl-CoA, during β-oxidation, FADH2 and NADH are also formed. In skeletal muscles, at rest, excess of ATP produced is stored as PCr. ATP is converted into ADP and Pi by ATPase, and the Pi is used to convert Cr in PCr whose amount is roughly 10 times higher than the amount of ATP. During intense activity, PCr can anaerobically donate a phosphate group to ADP and form ATP for quick regeneration of ATP. PCr is, therefore, a rapid system to supply energy during contraction. The reversible phosphorylation of Cr is catalyzed by several CK. Once ATP also produced by PCr is consumed, the AK (myokinase) catalyzes the formation of ATP and AMP from two ADP molecules. During exercise, the amount of ATP produced by the myofiber increases enormously. However, the stores of ATP that can be detected in the myofiber are not as high, as ATP is stored in the form of PCr. (B) Reducing equivalents (NADH and FADH2) generated mainly during TCA, β-oxidation, and glycolysis are oxidized by the complexes of the respiratory chain (Complex I, II, III, and IV) in the oxidative phosphorylation pathway. Electrons are transferred from NADH and FADH2 to oxygen (which is reduced to H2O) by means of the enzyme complexes and by the electron carriers Ub and Cyt c of the respiratory chain. The energy released by reducing equivalent oxidation as electrons pass from one complex to the next is used to pump protons (H+) across the IM into the intermembrane space. This creates an electrochemical proton gradient across the IM, which is highly energetic. Protons can flow along this gradient through ATP synthase (ATPase or complex V); this backflow releases the energy of the proton gradient, which is used by ATP synthase to phosphorylate ADP and to form ATP. This phosphorylation of ADP is called oxidative, as it is coupled to the presence of oxygen that enables the oxidation of reducing equivalents. By this mechanism, nutrients are oxidated and their energy is stored in usable energy as ATP. ATP is also produced in a lower amount during glycolysis. OM, outer membrane; Glu, glucose; FFAs, free fatty acids; Glu-6-P, glucose-6-phosphate; Pyr, pyruvate; PDH, pyruvate dehydrogenase; TCA, tricarboxylic acid; FAT/CD36, fatty acyl translocase; CPT, carnitine palmitoyltransferase; CK, creatine kinases; AK, adenylate kinase; Ub, ubiquinon; IM, inner membrane; Cr, creatine; Cyt c, cytochrome c; GLUT4, glucose transporter 4; HK, hexokinase; PCr, phosphocreatine.

Figure 6. Muscle metabolism

[Source ⁵²⁾]

Exercise-Induced Adaptation

Skeletal muscle is extremely adaptable to environmental changes and is characterized by a high metabolic flexibility: It is able to rapidly modify the rate of ATP synthesis, the blood flow, and the kind of substrate used, depending on needs ⁵³⁾. Skeletal muscle is also extremely adaptable to changes in contractile activity: Physical exercise strongly modifies metabolic potential, morphology, and physiology of skeletal muscle, thus producing a strong beneficial effect on health ⁵⁴⁾. All pathways of ATP generation are active during exercise, but the relative contribution of each is determined by the intensity and duration of contraction. Indeed, exercise might be performed with different modalities, thus producing different effects on muscles ⁵⁵⁾.

Physical exercise might be grossly classified as “endurance training” and “resistance training.” Endurance training is based on endurance and is aerobic, while resistance training is based on strength. Endurance exercise (e.g., performed by marathon runners, swimmers, and cyclists) is generally characterized by high-frequency, long duration, and low power output. Resistance exercise (e.g., body building and throwing events) is, in general, characterized by low frequency, high resistance, high intensity, and short duration. Along with the modality of exercise, other parameters such as duration, frequency, and intensity of the exercise influence the effect of physical training on the muscle ⁵⁶⁾.

Exercise triggers a metabolic and structural remodeling in skeletal muscle, thus leading to changes in contractile properties and to increased angiogenesis in order to reduce muscle fatigue. These adaptations improve skeletal muscle performance. The specific features of skeletal muscle adaptation to exercise depend on the modality of exercise performed. Resistance exercise acts mainly by increasing muscle mass and strength (see “Exercise and skeletal muscle mass” section). On the other hand, endurance exercise stimulates mitochondrial biogenesis and expression of mitochondrial respiration and FFA β-oxidation genes, thereby providing a phenotypic adaptation toward a more oxidative phenotype. Submaximal aerobic activities increase insulin-independent glucose uptake and utilization in skeletal muscle, along with insulin sensitivity and redistribution of GLUT4 to the plasma membrane ⁵⁷⁾. With regard to the contractile properties, endurance exercise promotes fiber type transformation toward the slow-twitch contractile apparatus by inducing a dramatic modification of gene expression and physiological properties of the myofiber. The muscle used frequently needs to be more energy efficient, with both longer twitches and slower MyHC types contributing to higher energy efficiency ⁵⁸⁾.

Exercise provides numerous beneficial effects on skeletal muscle and, in general, on health. Although both exercise modalities are beneficial for health, endurance exercise is more effective for preventing cardiovascular diseases; while resistance training (mostly inducing muscle hypertrophy) is more effective for the maintenance of muscle mass contrasting atrophy and age-related muscle wasting ⁵⁹⁾.

Exercise and skeletal muscle mass

As stated earlier, while endurance exercise acts by up-regulating mitochondrial metabolism and fiber-type transformation, the beneficial effects of resistance exercise mainly depend on its ability to increase muscle mass. Muscle fiber hypertrophy was a determinant of overall muscle enlargement as a result of resistance training. Although many training variables contribute to the performance, cellular and molecular adaptations to resistance exercise, relative intensity (% 1 repetition maximum [%1RM]) appears to be an important factor ⁶⁰⁾. This review summarises and analyses data from numerous resistance exercise training studies that have monitored percentage fibre type, fibre type cross-sectional areas, percentage cross-sectional areas, and myosin heavy chain (MyHC) isoform expression. In general, relative intensity appears to account for 18-35% of the variance for the muscle hypertrophy response to resistance exercise. On the other hand, fibre type and MyHC transitions were not related to the relative intensity used for training. When competitive lifters were compared, those typically utilising the heaviest loads (> or =90% 1RM), that is weightlifters and powerlifters, exhibited a preferential hypertrophy of type II fibres when compared with body builders who appear to equally hypertrophy both type I and type II fibres. These data suggest that maximal hypertrophy occurs with loads from 80-95% 1RM ⁶¹⁾.

Skeletal muscle mass depends on a delicate balance between protein synthesis and protein degradation: Resistance exercise influences both these processes by activating the phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signaling ⁶²⁾. The kinase mTOR exists in two independent complexes: mTOR complex 1 (mTORC1) and mTORC2. Raptor and Rictor are specific functional components of TORC1 and TORC2, respectively. mTORC1 controls protein translation by phosphorylating the eukaryotic translation initiation factor 4E-binding protein-1 (4E-BP1) and p70 ribosomal protein S6 kinase (p70S6K). p70S6K phosphorylates the ribosomal subunit S6 and up-regulates protein synthesis. mTORC2 prevents protein degradation by phosphorylating and inhibiting the forkhead box (FoxO) class of transcription factors. Indeed, FoxO transcription factors induce the expression of atrogin-1/muscle atrophy F-box (MAFbx) and muscle ring finger protein 1 (MuRF-1), two E3 ubiquitin ligases, which promote the ubiquitination and the proteasome-mediated degradation of critical sarcomeric proteins. The ubiquitin-proteasome system mediates muscle atrophy in several conditions, and the oxidative stress plays a key role in the regulation of the proteasome proteolytic activity. Mechanosensory regulation of protein synthesis is determined by high-force contractions that damage the sarcolemma and activate the membrane phospholipid phosphatidic acid, which, in turn, activates mTOR. During resistance exercise, mechanosensory regulation of protein synthesis also involves some transmembrane receptors called focal adhesion kinase (FAK) proteins, which transmit the contractile force through the skeletal muscle architecture and trigger protein synthesis by inducing mTOR activation.

The influence of exercise on muscle mass also involves muscle stem cells. As such, exercise induction of hypertrophy is accompanied by satellite cell fusion to myofibers. Mitochondria are considered as being involved in the regulation of myoblast proliferation/differentiation; therefore, PGC-1α-mediated mitochondrial biogenesis triggered by endurance exercise might possibly influence satellite cell fusion. Interestingly, PGC-1α up-regulation occurs during differentiation. Other signalings triggered by endurance exercise, such as p38 MAPK and Akt, contribute to satellite cell differentiation. Therefore, muscle wasting might be counteracted by endurance training through enhancement of myoblast differentiation and fusion. In addition, it has been suggested that PGC-1α might control muscle wasting pathways. It reduces the FoxO3-associated muscle atrophy, and mice overexpressing PGC-1α are protected from sarcopenia and have an increased lifespan. Moreover, increasing mitochondrial oxidative metabolism and biogenesis protects from atrophy, and this might be achieved by endurance exercise-induced PGC-1α. Regular submaximal aerobic activities have also been found to be beneficial for patients afflicted with Duchenne muscular dystrophy (DMD), while “exercise mimetics” decrease muscle inflammation and inhibit FoxO1 signaling. It has also been shown that exercise inhibits MuRF up-regulation due to diabetes and that this might mediate exercise’s beneficial effects on this disease.

At baseline levels, autophagy is a housekeeping mechanism cleaning cells of aberrant and dysfunctional molecules and organelles, thereby maintaining cell homeostasis. Autophagy is a multi-step process during which a part of the cytoplasm (including intracellular organelles) is sequestered within double-membraned autophagic vacuoles (autophagosomes), which then fuse to lysosomes and become autophagolysosomes (Figure 7). By this mechanism, defective organelles and proteins are digested by lysosomal hydrolases ⁶³⁾. Under stress conditions, autophagy increases and promotes temporary cellular adaptation to unfavorable conditions. It primarily favors survival during nutritional stress imposed by decreased nutrients; the degradation of intracellular material through autophagy becomes an alternative source of energy ⁶⁴⁾.

Autophagy and skeletal muscle mass maintenance

The role of autophagy in the maintenance of muscle mass is controversial. While excessive autophagy is detrimental to skeletal muscle and contributes to muscle wasting, basal autophagy is required for the maintenance of skeletal muscle homeostasis and integrity ⁶⁵⁾. The autophagy-lysosome system is activated in several atrophy conditions such as fasting, caloric restriction, cancer cachexia, aging, disuse, and denervation ⁶⁶⁾. Conversely, the key role of autophagy in skeletal muscle homeostasis maintenance is supported by the fact that muscle-specific ablation of key autophagy proteins such as Atg7 or Atg5 produces myofiber degeneration and muscle weakness ⁶⁷⁾. On the other hand, the autophagy-lysosome system is activated in several atrophy conditions such as fasting, caloric restriction, cancer cachexia, aging, disuse, and denervation ⁶⁸⁾. Moreover, the phenotype of some transgenic mice suggests that autophagy may favor muscle atrophy.

Increasing evidence suggests that exercise triggers autophagy in skeletal muscle and that autophagy mediates some beneficial effects due to exercise. Grumati et al. ⁶⁹⁾ have revealed an important connection between autophagy and exercise physiology. They have shown that physical training stimulates autophagy in mice skeletal muscles, and that autophagy was able to prevent the accumulation of damaged organelles and to maintain myofiber homeostasis.

It is currently believed that a correct balance between activation and inhibition of autophagy is critical for muscle homeostasis. Too much autophagy causes an excessive removal of crucial cellular components, which leads to muscle atrophy. On the other hand, insufficient autophagy leads to the accumulation of dysfunctional organelles, thus impairing myofiber homeostasis ⁷⁰⁾.

The involvement of autophagy in exercise-induced remodeling might be related to the two most important functions of autophagy: providing new sources of energy and removing dysfunctional organelles. During exercise, more energy is needed; the requirement of energy generally induces autophagy and it is possible that, as stated earlier, the increase of glucose uptake triggered by exercise depends on autophagy. Moreover, autophagy is the main mechanism for the removal of damaged mitochondria that is necessary to protect myfibers from atrophy. Damaged mitochondria removal is especially needed during exercise when oxidative metabolism and turnover of mitochondria increase. Interestingly, many of the sensors and pathways triggered by exercise in skeletal muscle are involved in the modulation of autophagy.

Figure 7. A general overview of the signaling molecules involved in the regulation of autophagy in skeletal muscles during exercise

[Source ⁷¹⁾]

What is the best way to build muscle ?

Skeletal muscle tissue is sensitive to the acute and chronic stresses associated with resistance (weight) training. These responses are influenced by the structure of resistance activity (i.e. frequency, load and recovery) as well as the training history of the individuals involved ⁷²⁾. There are histochemical and biochemical data which suggest that resistance (weight) training alters the expression of myosin heavy chains (MyHCs). Specifically, chronic exposure to bodybuilding and power lifting type activity produces shifts towards the MyHC I and IIb isoforms, respectively.

Although many training variables contribute to the performance, cellular and molecular adaptations to resistance exercise, relative intensity (% 1 repetition maximum [%1RM]) appears to be an important factor. In general, relative intensity appears to account for 18-35% of the variance for the muscle hypertrophy response to resistance exercise. On the other hand, fibre type and MyHC transitions were not related to the relative intensity used for training. When competitive lifters were compared, those typically utilising the heaviest loads (> or =90% 1RM), that is weightlifters and powerlifters, exhibited a preferential hypertrophy of type II fibres when compared with body builders who appear to equally hypertrophy both type I and type II fibres. These data suggest that maximal muscle hypertrophy occurs with loads from 80-95% 1RM ⁷³⁾.

Heavy resistance training is associated with increased body weight, lean body mass, and muscle cross-sectional area. The increased muscle cross-sectional area is mainly brought about by hypertrophy of individual muscle fibers ⁷⁴⁾. There is a greater increase in the area of fast twitch fibers compared to slow twitch fibers. In addition, long-term heavy resistance training may produce fiber proliferation. Mitochondrial volume density decreases in proportion to muscle hypertrophy in response to training. Typically, no capillary neoformation occurs during strength training. Therefore, capillary density decreases consequent to heavy resistance training. It appears, though, that bodybuilders, relying on a high repetition training system, in contrast to Olympic weight- and power lifters, display a small increase in number of capillaries per fiber. Enzyme activities, reflecting oxidative potential; decrease during long-term heavy resistance training, resulting in muscle hypertrophy. Although glycogen storage capacity is enhanced in strength trained athletes, enzyme activities reflecting anaerobic metabolism do not increase in response to heavy resistance exercise.

In a study ⁷⁵⁾ to investigate the “strength-endurance continuum”, thirty-two untrained men (average age 22.5 years, height 178.3 cm, body mass 77.8 kg) participated in an 8-week progressive resistance-training program.

Subjects were divided into four groups:

• a low repetition group (Low Rep) performing 3-5 repetitions maximum (RM) for four sets of each exercise with 3 min rest between sets and exercises,
• an intermediate repetition group (Int Rep) performing 9-11 repetitions maximum (RM) for three sets with 2 min rest,
• a high repetition group (High Rep) performing 20-28 repetitions maximum (RM) for two sets with 1 min rest, and
• a non-exercising control group (Control).

Three exercises (leg press, squat, and knee extension) were performed 2 days/week for the first 4 weeks and 3 days/week for the final 4 weeks. Maximal strength (one repetition maximum, 1RM), local muscular endurance (maximal number of repetitions performed with 60% of 1RM), and various cardiorespiratory parameters (e.g., maximum oxygen consumption, pulmonary ventilation, maximal aerobic power, time to exhaustion) were assessed at the beginning and end of the study. In addition, pre- and post-training muscle biopsy samples were analyzed for fiber-type composition, cross-sectional area, myosin heavy chain (MyHC) content, and capillarization.

Maximal strength improved significantly more for the Low Rep group compared to the other training groups, and the maximal number of repetitions at 60% 1RM improved the most for the High Rep group. In addition, maximal aerobic power and time to exhaustion significantly increased at the end of the study for only the High Rep group. All three major fiber types (types I, IIA, and IIB) hypertrophied for the Low Rep and Int Rep groups, whereas no significant increases were demonstrated for either the High Rep or Control groups. However, the percentage of type IIB fibers decreased, with a concomitant increase in IIAB fibers for all three resistance-trained groups. These fiber-type conversions were supported by a significant decrease in MyHCIIb accompanied by a significant increase in MyHCIIa. No significant changes in fiber-type composition were found in the control (non-exercise) samples. Although all three training regimens resulted in similar fiber-type transformations (IIB to IIA), the low to intermediate repetition resistance-training programs induced a greater hypertrophic effect compared to the high repetition regimen. The High Rep group, however, appeared better adapted for submaximal, prolonged contractions, with significant increases after training in aerobic power and time to exhaustion. Thus, low and intermediate RM training appears to induce similar muscular adaptations, at least after short-term training in previously untrained subjects. Overall, however, these data demonstrate that both physical performance and the associated physiological adaptations are linked to the intensity and number of repetitions performed, and thus lend support to the “strength-endurance continuum”.

In another study ⁷⁶⁾ to assess the relationships between human muscle fiber hypertrophy, protein isoform content and maximal Ca2+-activated contractile function following a short-term period of resistance exercise training. Widrick and colleagues ⁷⁷⁾ put 6 healthy sedentary men (average age 27 yr, height 178 cm, and weight 82.3 kg) under a resistance exercise training program consisting of 36 exercise sessions performed three times per week on nonconsecutive days. The training program used free-weight and machine-based exercises designed to overload the major lower (squats, knee extension, knee flexion, calf raises), upper (bench press, lat pull down, shoulder press, triceps press, biceps curl, seated row), and abdominal muscle groups. During each training session, subjects completed three sets of 5–10 of the exercises listed above (divided approximately equally between those targeting the upper and lower body). Subjects performed 12 repetitions per set during the first 2 wk of the training program. Thereafter, one weekly session was performed at 10 repetitions per set, the second session at 8 repetitions per set, and the third weekly session at 6 repetitions per set. During all sessions, the training resistance was adjusted so that subjects were able to complete only the specified number of repetitions, plus or minus one repetition. This nonlinear periodized program was used to maximize training adaptations. All exercise sessions were supervised by one of the investigators or by a trained assistant.

After 12 weeks of exercise, the volunteers lean body mass rose 4% over the course of the training program (from 63.7 ± 2.8 to 66.4 ± 2.3 kg), whereas total body mass was unchanged. Lower body neuromuscular strength, as assessed by the six-repetition maximum for leg press exercise, rose from a pretraining value of 1,524 ± 99 to 1,791 ± 69 N at the 4th week; 2,241 ± 117 N at the 8th week and 2,532 ± 115 N at the 12th week of training. Over the course of the training program, leg press six-repetition maximum strength increased 62% relative to total body mass (from 18.5 ± 0.8 to 30.0 ± 1.5 N/kg body mass) or 61% relative to lean body mass (from 23.8 ± 0.7 to 38.3 ± 2.1 N/kg lean body mass).

The relative number of fibers containing type IIa MyHC increased from 30% before training to 55% after training, whereas the relative number of single fibers containing type IIa and type IIx MyHC fell from 22 to 3%. Posttraining fibers containing type IIx or type I/IIa MyHC were relatively rare. Consequently, 94% of the pre- and 100% of the posttraining fibers studied contained either type I, type IIa, or type IIa/IIx MyHC ⁷⁸⁾. The results after twelve weeks of progressive resistance exercise training, sufficient to increase neuromuscular strength by >60%, resulted in significant hypertrophy of fibers containing type I, IIa, or IIa/IIx MyHC. Peak Ca2+-activated force and absolute peak power rose in direct proportion with the increase in fiber cross sectional area, whereas unloaded shortening velocity and power per fiber volume were unaffected by training. These data are consistent with the resistance training-induced increases in slow- and fast-fiber cross-sectional area reported in the histochemical literature ⁷⁹⁾, ⁸⁰⁾. It seems likely that the increased neuromuscular power observed after strength training is due, at least in part, to the greater potential of individual muscle fibers to produce power. Although both type I and II fibers hypertrophied, the type II fibers demonstrated a greater capacity for hypertrophy, were more varied in their range of sizes, and were larger than type I fibers both pre- and posttraining. The contribution of the type II fibers would be particularly important in this regard as they produce sixfold greater power than the type I fibers. In conclusion, resistance training resulted in hypertrophy of the total muscle cross sectional area and fiber areas with no change in estimated fiber number, whereas increase in capillary number were proportional to muscle fiber growth.

The effects of diet types (macronutrient composition; eating styles) and their influence on body composition

Diets primarily focused on fat loss are driven by a sustained caloric deficit. The higher the baseline body fat level, the more aggressively the caloric deficit may be imposed ⁸¹⁾. However, a slower rates of weight loss can better preserve lean mass in leaner subjects.

Caloric intake

In determining an appropriate caloric intake, it should be noted that the tissue lost during the course of an energy deficit is influenced by the size of the energy deficit. While greater deficits yield faster weight loss, the percentage of weight loss coming from lean body mass (LBM) tends to increase as the size of the deficit increases ⁸²⁾, ⁸³⁾, ⁸⁴⁾. In studies of weight loss rates, weekly losses of 1 kg compared to 0.5 kg over 4 weeks resulted in a 5% decrease in bench press strength and a 30% greater reduction in testosterone levels in strength training women ⁸⁵⁾. Weekly weight loss rates of 1.4% of bodyweight compared to 0.7% in athletes during caloric restriction lasting four to eleven weeks resulted in reductions of fat mass of 21% in the faster weight loss group and 31% in the slower loss group. In addition, LBM increased on average by 2.1% in the slower loss group while remaining unchanged in the faster loss group. Worthy of note, small amounts of LBM were lost among leaner subjects in the faster loss group ⁸⁶⁾.

Therefore, weight loss rates that are more gradual may be superior for LBM retention. At a loss rate of 0.5 kg per week (assuming a majority of weight lost is fat mass), a 70 kg athlete at 13% body fat would need to be no more than 6 kg to 7 kg over their contest weight in order to achieve the lowest body fat percentages recorded in competitive bodybuilders following a traditional three month preparation ⁸⁷⁾, ⁸⁸⁾. If a competitor is not this lean at the start of the preparation, faster weight loss will be required which may carry a greater risk for LBM loss.

In a study of bodybuilders during the twelve weeks before competition, male competitors reduced their caloric intake significantly during the latter half and subsequently lost the greatest amount of LBM in the final three weeks ⁸⁹⁾. Therefore, diets longer than two to four months yielding weight loss of approximately 0.5 to 1% of bodyweight weekly may be superior for LBM retention compared to shorter or more aggressive diets. Ample time should be allotted to lose body fat to avoid an aggressive deficit and the length of preparation should be tailored to the competitor; those leaner dieting for shorter periods than those with higher body fat percentages. It must also be taken into consideration that the leaner the competitor becomes the greater the risk for LBM loss ⁹⁰⁾, ⁹¹⁾. As the availability of adipose tissue declines the likelihood of muscle loss increases, thus it may be best to pursue a more gradual approach to weight loss towards the end of the preparation diet compared to the beginning to avoid LBM loss.

• Diets focused primarily on gaining lean mass are driven by a sustained caloric surplus to facilitate anabolic processes and support increasing resistance-training demands ⁹²⁾. The composition and magnitude of the surplus, as well as training status of the subjects can influence the nature of the gains.

• A wide range of dietary approaches (low-fat to low-carbohydrate/ketogenic diets and all points between) can be similarly effective for improving body composition.

• Bodybuilders typically employ a higher meal frequency in an attempt to optimize fat loss and muscle preservation. However, the majority of chronic experimental studies have failed to show that different meal frequencies have different influences on bodyweight or body composition ⁹³⁾, ⁹⁴⁾, ⁹⁵⁾. Despite this limitation, the available research has consistently refuted the popular belief that a grazing pattern (smaller, more frequent meals) raises energy expenditure compared to a gorging pattern (larger, less frequent meals). Disparate feeding patterns ranging from two to seven meals per day have been compared in tightly controlled studies using metabolic chambers, and no significant differences in 24-hour thermogenesis have been detected ⁹⁶⁾, ⁹⁷⁾. Along these lines, Stote et al. [113] found that compared to three meals per day, one meal per day caused slightly more weight and fat loss. Curiously, the one meal per day group also showed a slight gain in lean mass, but this could have been due to the inherent error in the use of bioelectrical impedance analysis (BIA) to measure body composition for body composition assessment ⁹⁸⁾.

• Increasing dietary protein to levels significantly beyond current recommendations for athletic populations may result in improved body composition. The International Society of Sports Nutrition’s original 2007 position stand on protein intake (1.4–2.0 g/kg) ⁹⁹⁾ has gained further support from subsequent investigations arriving at similar requirements in athletic populations ¹⁰⁰⁾, ¹⁰¹⁾, ¹⁰²⁾, ¹⁰³⁾, ¹⁰⁴⁾, ¹⁰⁵⁾.

• Higher protein intakes (2.3–3.1 g/kg lean mass) may be required to maximize muscle retention in lean, resistance-trained subjects under hypocaloric conditions. Emerging research on very high protein intakes (>3 g/kg) has demonstrated that the known thermic, satiating, and lean-mass-preserving effects of dietary protein might be amplified in resistance-training subjects.

• The collective body of intermittent caloric restriction (intermittent fasting) research demonstrates no significant advantage over daily caloric restriction for improving body composition. Time-restricted feeding typically involves a fasting period of 16–20 hours and a feeding period of 4–8 hours daily. Unsurprisingly, significant weight loss occurs, and this includes a reduction in lean mass as well as fat mass ¹⁰⁶⁾, ¹⁰⁷⁾. An 8-week trial by Tinsley et al. ¹⁰⁸⁾ examined the effect of a 20-hour fasting/4-hour feeding protocol (20/4) done 4 days per week on recreationally active, but untrained subjects. No limitations were placed on the amounts and types of food consumed in the 4-hour eating window. A standardized resistance training program was administered 3 days per week. The time-restricted feeding group lost body weight, due to a significantly lower energy intake (667 kcal less on fasting compared to non-fasting days). Cross sectional area of the biceps brachii and rectus femoris increased similarly in both the time-restricted feeding and normal diet group. No significant changes in body composition (via DXA) were seen between groups. Despite a lack of statistical significance, there were notable effect size differences in lean soft tissue (normal diet gained 2.3 kg, while time-restricted feeding lost 0.2 kg). Although both groups increased strength without significant between-group differences, effect sizes were greater in the time-restricted feeding group for bench press endurance, hip sled endurance, and maximal hip sled strength. This finding should be viewed cautiously given the potential for greater and more variable neurological gains in untrained subjects. A subsequent study by Moro et al. ¹⁰⁹⁾ found that in resistance-trained subjects on a standardized training protocol, a 16-hour fasting/8-hour feeding cycle (16/8) resulted in significantly greater fat loss in time-restricted feeding vs. normal diet control group (ND) (1.62 vs. 0.31 kg), with no significant changes in lean mass in either group. Time-restricted feeding’s meals were consumed at 1 pm, 4 pm, and 8 pm. Normal diet’s meals were consumed at 8 am, 1 pm, and 8 pm. Macronutrient intake between the time-restricted feeding and normal diet groups was matched, unlike the aforementioned Tinsley et al. study ¹¹⁰⁾ whereby protein intake was disparate and sub-optimal (1.0 g/kg in the time-restricted feeding group and 1.4 g/kg in the normal diet control group). Subjects in the present study’s time-restricted feeding and normal diet group consumed 1.93 and 1.89 g/kg, respectively. The mechanisms underlying these results are not clear. The authors speculated that increased adiponectin levels in the time-restricted feeding group could have stimulated mitochondrial biogenesis via interacting with PPAR-gamma, in addition to adiponectin acting centrally to increase energy expenditure. However, the time-restricted feeding group also experienced unfavorable changes such as decreased testosterone and triiodothyronine levels.

• Seimon et al. ¹¹¹⁾ recently published the largest systematic review of intermittent fasting research to date, comparing the effects of intermittent energy restriction (IER) to continuous energy restriction (CER) on body weight, body composition, and other clinical parameters. Their review included 40 studies in total, 12 of which directly compared an intermittent energy restriction (IER) with a continuous energy restriction (CER) condition. They found that overall, the two diet types resulted in “apparently equivalent outcomes” in terms of body weight reduction and body composition change. Interestingly, intermittent energy restriction (IER) was found to be superior at suppressing hunger. The authors speculated that this might be attributable to ketone production in the fasting phases. However, this effect was immaterial since on the whole, intermittent fasting failed to result in superior improvements in body composition or greater weight loss compared to continuous energy restriction (CER). Table 1 outlines the characteristics of the major diet archetypes.

• Dehydration: In an attempt to enhance muscle size and definition by reducing extracellular water content, many bodybuilders engage in fluid, electrolyte, and carbohydrate manipulation in the final days and hours before competing ¹¹²⁾, ¹¹³⁾. The effect of electrolyte manipulation and dehydration on visual appearance has not been studied, however it may be a dangerous practice ¹¹⁴⁾. Furthermore, dehydration could plausibly degrade appearance considering that extracellular water is not only present in the subcutaneous layer. A significant amount is located in the vascular system. Thus, the common practice of “pumping up” to increase muscle size and definition by increasing blood flow to the muscle with light, repetitive weight lifting prior to stepping on stage ¹¹⁵⁾ could be compromised by dehydration or electrolyte imbalance. Furthermore, dehydration reduces total body hydration. A large percentage of muscle tissue mass is water and dehydration results in decreases in muscle water content ¹¹⁶⁾ and therefore muscle size, which may negatively impact the appearance of muscularity. At this time it is unknown whether dehydration or electrolyte manipulation improves physique appearance. What is known is that these practices are dangerous and have the potential to worsen it. It is unclear if carbohydrate loading has an impact on appearance and if so, how significant the effect is. However, the recommended muscle-sparing practice by some researchers to increase the carbohydrate content of the diet in the final weeks of preparation ¹¹⁷⁾ might achieve any proposed theoretical benefits of carbohydrate loading. If carbohydrate loading is utilized, a trial run before competition once the competitor has reached or nearly reached competition leanness should be attempted to develop an individualized strategy. However, a week spent on a trial run consuming increased carbohydrates and calories may slow fat loss, thus ample time in the diet would be required.

• Carbohydrate Loading: In the final days before competing, bodybuilders commonly practice carbohydrate loading similar to endurance athletes in an attempt to raise muscle-glycogen levels and increase muscle size ¹¹⁸⁾, ¹¹⁹⁾, ¹²⁰⁾, ¹²¹⁾. In the only direct study of this practice, no significant quantitative change in muscle girth was found to occur [208]. However, an isocaloric diet was used, with only a change in the percentage of carbohydrate contributing to the diet. If total calories had also been increased, greater levels of glycogen might have been stored which could have changed the outcome of this study. Additionally, unlike the subjects in this study bodybuilders prior to carbohydrate loading have reduced glycogen levels from a long calorically restricted diet and it is possible in this state that carbohydrate loading might effect a visual change. Furthermore, bodybuilding performance is measured subjectively, thus analysis of girth alone may not discern subtle visual changes which impact competitive success. Lastly, some bodybuilders alter the amount of carbohydrate loaded based on the visual outcome, increasing the amount if the desired visual change does not occur ¹²²⁾. Thus, an analysis of a static carbohydrate load may not accurately represent the dynamic nature of actual carbohydrate loading practices.In fact, in an observational study of competitive bodybuilders in the days before competition who loaded carbohydrates, subjects showed a 4.9% increase in biceps thickness the final day before competition compared to six weeks prior ¹²³⁾. Although it is unknown if this was caused by increased muscle glycogen, it is unlikely it was due to muscle mass accrual since the final weeks of preparation are often marked by decreases not increases in lean mass ¹²⁴⁾. Future studies of this practice should include a qualitative analysis of visual changes and analyze the effects of concurrent increases in percentage of carbohydrates as well as total calories.

Table 1. Diet categories

Diet	Composition	Strengths	Limitations
Low-energy diets (LED)	LED: 800–1200 kcal/day VLED: 400–800 kcal/day	Rapid weight loss (1.0–2.5 kg/week, diets involve premade products that eliminate or minimize the need for cooking and planning.	VLED have a higher risk for more severe side-effects, but do not necessary outperform LED in the long-term
Low-fat diets (LFD)	LFD: 25–30% fat VLFD: 10–20% fat	LFD have the support of the major health organizations due to their large evidence basis in the literature on health effects. Flexible macronutrient range. Does not indiscriminately vilify foods based on CHO content.	Upper limits of fat allowance may falsely convey the message that dietary fat is inherently antagonistic to body fat reduction. VLFD have a scarce evidence basis in terms of comparative effects on body composition, and extremes can challenge adherence.
Low-carbohydrate diets (LCD)	50–150 g CHO, or up to 40% of kcals from CHO	Defaults to higher protein intake. Large amount of flexibility in macronutrient proportion, and by extension, flexibility in food choices. Does not indiscriminately prohibit foods based on fat content.	Upper limits of CHO allowance may falsely convey the message that CHO is inherently antagonistic to body fat reduction.
Ketogenic diets (KD)	Maximum of ~50 g CHO Maximum of ~10% CHO	Defaults to higher protein intake. Suppresses appetite/controls hunger, causes spontaneous reductions in kcal intake under non-calorically restricted conditions. Simplifies the diet planning and decision-making process.	Excludes/minimizes high-CHO foods which can be nutrient dense and disease-preventive. Can compromise high-intensity training output. Has not shown superior effects on body composition compared to non-KD when protein and kcals are matched. Dietary extremes can challenge long-term adherence.
High-protein diets (HPD)	HPD: ≥ 25% of total kcals, or 1.2–1.6 g/kg (or more) Super HPD: > 3 g/kg	HPD have a substantial evidence basis for improving body composition compared to RDA levels (0.8 g/kg), especially when combined with training. Super-HPD have an emerging evidence basis for use in trained subjects seeking to maximize intake with minimal-to-positive impacts on body composition.	May cause spontaneous reductions in total energy intake that can antagonize the goal of weight gain. Potentially an economical challenge, depending on the sources. High protein intakes could potentially displace intake of other macronutrients, leading to sub-optimal intakes (especially CHO) for athletic performance goals.
Intermittent fasting (IF)	Alternate-day fasting (ADF): alternating 24-h fast, 24-h feed. Whole-day fasting (WDF): 1–2 complete days of fasting per week. Time-restricted feeding (TRF): 16–20-h fast, 4–8-h feed, daily.	ADF, WDF, and TRF have a relatively strong evidence basis for performing equally and sometimes outperforming daily caloric restriction for improving body composition. ADF and WDF have ad libitum feeding cycles and thus do not involve precise tracking of intake. TRF combined with training has an emerging evidence basis for the fat loss while maintaining strength.	Questions remain about whether IF could outperform daily linear or evenly distributed intakes for the goal of maximizing muscle strength and hypertrophy. IF warrants caution and careful planning in programs that require optimal athletic performance.

[Source ¹²⁵⁾]

• The long-term success of a diet depends upon compliance and suppression or circumvention of mitigating factors such as adaptive thermogenesis. Joosen and Westerterp ¹²⁶⁾ examined the literature (11 studies) to see if “adaptive thermogenesis” existed in overeating experiments. No evidence beyond the theoretical costs of increased body size and thermic effect of food were found. Nevertheless, there is substantial interindividual variability in the energetic response to overfeeding. They found in overfeeding experiments, weight gain is often less than expected from the energy excess intake. In part this is the result of an obligatory increase in energy expenditure associated with the increased body weight and lean mass ¹²⁷⁾ and the larger amount of food to be digested and absorbed ¹²⁸⁾. However, evidence for adaptive thermogenesis as a mechanism to explain interindividual differences in weight gain on the same overeating regimen is still inconsistent and hard to prove ¹²⁹⁾

• There is a paucity of research on women and older populations, as well as a wide range of untapped permutations of feeding frequency and macronutrient distribution at various energetic balances combined with training. Behavioral and lifestyle modification strategies are still poorly researched areas of weight management.

Role of Protein and Amino Acids in promoting Lean Mass gain with resistance exercise

Amino acids are major nutrient regulators of muscle protein turnover. After protein ingestion, hyperaminoacidemia stimulates increased rates of skeletal muscle protein synthesis, suppresses muscle protein breakdown and promotes net muscle protein gain for several hours ¹³⁰⁾. These acute observations form the basis for strategized protein intake to promote lean mass gain, or prevent lean mass loss over the long term. However, factors such as protein dose, protein source, and timing of intake are important in mediating the anabolic effects of amino acids on skeletal muscle and must be considered within the context of evaluating the reported efficacy of long-term studies investigating protein supplementation as part of a dietary strategy to promote lean mass accretion and/or prevent lean mass loss. Current research suggests that dietary protein supplementation can augment resistance exercise-mediated gains in skeletal muscle mass and strength and can preserve skeletal muscle mass during periods of diet-induced energy restriction ¹³¹⁾. Perhaps less appreciated, protein supplementation can augment resistance training-mediated gains in skeletal muscle mass even in individuals habitually consuming ‘adequate’ (i.e., >0.8 g kg/day) protein. Additionally, overfeeding energy with moderate to high-protein intake (15–25 % protein or 1.8–3.0 g kg/day) is associated with lean, but not fat mass accretion, when compared to overfeeding energy with low protein intake (5 % protein or ~0.68 g kg/day) ¹³²⁾. Amino acids represent primary nutrient regulators of skeletal muscle anabolism, capable of enhancing lean mass accretion with resistance exercise and attenuating the loss of lean mass during periods of energy deficit, although factors such as protein dose, protein source, and timing of intake are likely important in mediating these effects.

Adequate Protein Consumption

In a review by Phillips and Van Loon [28], it is suggested that a protein intake of 1.8-2.7 g/kg for athletes training in hypocaloric conditions may be optimal. While this is one of the only recommendations existing that targets athletes during caloric restriction, this recommendation is not given with consideration to bodybuilders performing concurrent endurance and resistance training at very low levels of body fat. The collective agreement among reviewers is that a protein intake of 1.2-2.2 g/kg is sufficient to allow adaptation to training for athletes whom are at or above their energy needs ¹³³⁾, ¹³⁴⁾. However, bodybuilders during their contest preparation period typically perform resistance and cardiovascular training, restrict calories and achieve very lean conditions ¹³⁵⁾, ¹³⁶⁾. Each of these factors increases protein requirements and when compounded may further increase protein needs ¹³⁷⁾. Therefore, optimal protein intakes for bodybuilders during contest preparation may be significantly higher than existing recommendations. However, the recently published systematic review by Helms et al. ¹³⁸⁾ on protein intakes in resistance-trained, lean athletes during caloric restriction suggests a range of 2.3-3.1 g/kg of LBM, which may be more appropriate for bodybuilding. Moreover, the authors suggest that the lower the body fat of the individual, the greater the imposed caloric deficit and when the primary goal is to retain LBM, the higher the protein intake (within the range of 2.3-3.1 g/kg of LBM) should be.

Carbohydrate Intake

While it is true that resistance training utilizes glycogen as its main fuel source ¹³⁹⁾, total caloric expenditure of strength athletes is less than that of mixed sport and endurance athletes. Thus, authors of a recent review recommend that carbohydrate intakes for strength sports, including bodybuilding, be between 4–7 g/kg depending on the phase of training ¹⁴⁰⁾. However, in the specific case of a bodybuilder in contest preparation, achieving the necessary caloric deficit while consuming adequate protein and fat would likely not allow consumption at the higher end of this recommendation.

Satiety and fat loss generally improve with lower carbohydrate diets; specifically with higher protein to carbohydrate ratios ¹⁴¹⁾, ¹⁴²⁾. In terms of performance and health, low carbohydrate diets are not necessarily as detrimental as typically espoused ¹⁴³⁾. In a recent review, it was recommended for strength athletes training in a calorically restricted state to reduce carbohydrate content while increasing protein to maximize fat oxidation and preserve LBM ¹⁴⁴⁾. However, the optimal reduction of carbohydrate and point at which carbohydrate reduction becomes detrimental likely needs to be determined individually.

While it appears low carbohydrate, high protein diets can be effective for weight loss, a practical carbohydrate threshold appears to exist where further reductions negatively impact performance and put one at risk for LBM losses. In support of this notion, researchers studying bodybuilders during the final 11 weeks of contest preparation concluded that had they increased carbohydrate during the final weeks of their diet they may have mitigated metabolic and hormonal adaptations that were associated with reductions in LBM ¹⁴⁵⁾.

Therefore, once a competitor has reached or has nearly reached the desired level of leanness, it may be a viable strategy to reduce the caloric deficit by an increase in carbohydrate. For example, if a competitor has reached competition body fat levels (lacking any visible subcutaneous fat) and is losing half a kilogram per week (approximately a 500 kcals caloric deficit), carbohydrate could be increased by 25-50 g, thereby reducing the caloric deficit by 100-200 kcals in an effort to maintain performance and LBM. However, it should be noted that like losses of LBM, decrements in performance may not affect the competitive outcome for a bodybuilder. It is possible that competitors who reach the leanest condition may experience unavoidable drops in performance.

Fat Intake

Body composition and caloric restriction may play greater roles in influencing testosterone levels that fat intake. During starvation, a reduction in testosterone occurs in normal weight, but not obese, males ¹⁴⁶⁾. In addition, rate of weight loss may influence testosterone levels. Weekly target weight loss rates of 1 kg resulted in a 30% reduction in testosterone compared to target weight loss rates of 0.5 kg per week in resistance trained women of normal weight ¹⁴⁷⁾.

Reductions in the percentage of dietary fat in isocaloric diets from approximately 40% to 20% has resulted in modest, but significant, reductions in testosterone levels ¹⁴⁸⁾. However, distinguishing the effects of reducing total dietary fat on hormonal levels from changes in caloric intake and percentages of saturated and unsaturated fatty acids in the diet is difficult ¹⁴⁹⁾. However, a drop in testosterone does not equate to a reduction in LBM. In direct studies of resistance trained athletes undergoing calorically restricted high protein diets, low fat interventions that maintain carbohydrate levels appear to be more effective at preventing LBM loses than lower carbohydrate, higher fat approaches. These results might indicate that attempting to maintain resistance training performance with higher carbohydrate intakes is more effective for LBM retention than attempting to maintain testosterone levels with higher fat intakes.

While cogent arguments for fat intakes between 20 to 30% of calories have been made to optimize testosterone levels in strength athletes ¹⁵⁰⁾, in some cases this intake may be unrealistic in the context of caloric restriction without compromising sufficient protein or carbohydrate intakes. While dieting, low carbohydrate diets may degrade performance ¹⁵¹⁾ and lead to lowered insulin and IGF-1 which appear to be more closely correlated to LBM preservation than testosterone ¹⁵²⁾. Thus, a lower end fat intake between 15-20% of calories, which has been previously recommended for bodybuilders ¹⁵³⁾, can be deemed appropriate if higher percentages would reduce carbohydrate or protein below ideal ranges.

Table 2. Dietary recommendations for bodybuilding contest preparation

Diet component	Recommendation
Protein (g/kg of LBM)	2.3-3.1
Fat (% of total calories)	15-30%
Carbohydrate (% of total calories)	remaining
Weekly weight loss (% of body weight)	0.5-1%

[Source ¹⁵⁴⁾]

Note: It must be noted that there is a high degree of variability in the way that individuals respond to diets. If training performance degrades it may prove beneficial to decrease the percentage of calories from dietary fat within these ranges in favor of a greater proportion of carbohydrate. Finally, while outside of the norm, some competitors may find that they respond better to diets that are higher in fat and lower in carbohydrate than recommended in this review. Therefore, monitoring of individual response over a competitive career is suggested. There is no evidence of any relationships with bone structure or regional subcutaneous fat distribution with any response to specific macronutrient ratios in bodybuilders or athletic populations. Bodybuilders, like others athletes, most likely operate best on balanced macronutrient intakes tailored to the energy demands of their sport ¹⁵⁵⁾. While the majority of competitors will respond best to the fat and carbohydrate guidelines proposed, the occasional competitor will undoubtedly respond better to a diet that falls outside of these suggested ranges. Careful monitoring over the course of a competitive career is required to determine the optimal macronutrient ratio for pre-contest dieting.

Timing and consumption of protein and/or carbohydrate during workouts

Questions remain about the utility of consuming protein and/or carbohydrate during bodybuilding-oriented training bouts. Since these bouts typically do not resemble endurance bouts lasting 2 hours or more, nutrient consumption during training is not likely to yield any additional performance-enhancing or muscle -sparing benefits if proper pre-workout nutrition is in place. In the exceptional case of resistance training sessions that approach or exceed two hours of exhaustive, continuous work, it might be prudent to employ tactics that maximize endurance capacity while minimizing muscle damage. This would involve approximately 8–15 g protein co-ingested with 30–60 g carbohydrate in a 6-8% solution per hour of training ¹⁵⁶⁾. Nutrient timing is an intriguing area of study that focuses on what might clinch the competitive edge. In terms of practical application to resistance training bouts of typical length, Aragon and Schoenfeld ¹⁵⁷⁾ recently suggested a protein dose corresponding with 0.4-0.5 g/kg bodyweight consumed at both the pre- and post-exercise periods. However, for objectives relevant to bodybuilding, the current evidence indicates that the global macronutrient composition of the diet is likely the most important nutritional variable related to chronic training adaptations. Table 3 below provides a continuum of importance with bodybuilding-specific context for nutrient timing.

Table 3. Continuum of nutrient & supplement timing importance

[Source ¹⁵⁸⁾]

Nutritional Supplements

Some bodybuilders and athletes turn to dietary supplements to help them increase muscle size and definition ¹⁵⁹⁾. However, many bodybuilding products marketed as dietary supplements have been found to contain other ingredients that can be harmful. Use caution and talk with your health care provider before you begin taking any supplement to gain strength or muscle size. Furthermore, natural bodybuilding federations have extensive banned substance lists ¹⁶⁰⁾. It should be noted that there are considerably more supplements that are used by bodybuilders and sold on the market. However, an exhaustive review of all of the supplements commonly used by bodybuilders that often lack supporting data is beyond the scope of this article.

• Multivitamin and mineral supplements are unnecessary for athletes or other physically active people who eat a well-balanced diet and enough calories. The safety of supplements used for bodybuilding remains an issue of concern (see Safety below).

• There is no scientific evidence that other dietary supplements, such as choline, methoxyisoflavone, zinc/magnesium aspartate, nitric oxide precursors, and chromium, are effective for building strength and muscle mass.

• Evidence suggests that creatine, a popular dietary supplement, may enhance the effects of vigorous exercise on strength, muscle mass, and endurance, but it may also cause fluid weight gain, nausea, cramping, and diarrhea.

Safety

• Many bodybuilding products marketed as dietary supplements have been found to be deceptively labeled and to contain hidden ingredients that can be harmful, such as anabolic steroids, compounds chemically similar to them, or other substances that don’t qualify as dietary ingredients.

• In April 2013, the U.S. Food and Drug Administration issued a warning to consumers to avoid products containing the stimulant dimethylamylamine (DMAA). DMAA can elevate blood pressure and lead to other problems, such as a heart attack.

• Evidence suggests that creatine (an amino acid produced by the body) supplements may be safe for short-term use in healthy adults, but the American College of Sports Medicine recommends against anyone younger than age 18 using it to enhance athletic performance.

• Some dietary supplements may have side effects and some may interact with drugs or other supplements. Some vitamins and minerals are harmful at high doses. Talk with your health care provider before using a dietary supplement to increase muscle size and strength.

Micronutrients

Several previous studies have observed deficiencies in intakes of micronutrients, such as vitamin D, calcium, zinc, magnesium, and iron, in dieting bodybuilders ¹⁶¹⁾, ¹⁶²⁾. However, it should be noted that these studies were all published nearly 2 decades ago and that micronutrient deficiencies likely occurred due to elimination of foods or food groups and monotony of food selection ¹⁶³⁾, ¹⁶⁴⁾. Therefore, future studies are needed to determine if these deficiencies would present while eating a variety of foods and using the contest preparation approach described herein. Although the current prevalence of micronutrient deficiencies in competitive bodybuilders is unknown, based on the previous literature, a low-dose micronutrient supplement may be beneficial for natural bodybuilders during contest preparation; however, future studies are needed to verify this recommendation.

Caffeine

Caffeine is perhaps the most common pre-workout stimulant consumed by bodybuilders. Numerous studies support the use of caffeine to improve performance during endurance training ¹⁶⁵⁾, ¹⁶⁶⁾, sprinting ¹⁶⁷⁾, ¹⁶⁸⁾, and strength training ¹⁶⁹⁾, ¹⁷⁰⁾, ¹⁷¹⁾. However, not all studies support use of caffeine to improve performance in strength training ¹⁷²⁾, ¹⁷³⁾. It should be noted that many of the studies that found increases in strength training performance supplemented with larger (5–6 mg/kg) dosages of caffeine. However, this dosage of caffeine is at the end of dosages that are considered safe (6 mg/kg/day) ¹⁷⁴⁾. Additionally, it appears that regular consumption of caffeine may result in a reduction of ergogenic effects ¹⁷⁵⁾. Therefore, it appears that 5–6 mg/kg caffeine taken prior to exercise is effective in improving exercise performance; however, caffeine use may need to be cycled in order for athletes to obtain the maximum performance enhancing effect.

Beta-alanine

Beta-alanine (BA) is becoming an increasingly popular supplement among bodybuilders. Once consumed, BA enters the circulation and is up-taken by skeletal muscle where it is used to synthesize carnosine, a pH buffer in muscle that is particularly important during anaerobic exercise such as sprinting or weightlifting ¹⁷⁶⁾. Indeed, consumption of 6.4 g BA daily for four weeks has been shown to increase muscle carnosine levels by 64.2% ¹⁷⁷⁾. Moreover, supplementation with BA for 4–10 weeks has been shown to increase knee extension torque by up to 6%, improve workload and time to fatigue during high intensity cardio, improve muscle resistance to fatigue during strength training, increase lean mass by approximately 1 kg and significantly reduce perceptions of fatigue. Additionally, the combination of BA and CM may increase performance of high intensity endurance exercise and has been shown to increase lean mass and decrease body fat percentage more than CM alone. However, not all studies have shown improvements in performance with BA supplementation. To clarify these discrepancies, Hobson et al. ¹⁷⁸⁾ conducted a meta-analysis of 15 studies on BA supplementation and concluded that BA significantly increased exercise capacity and improved exercise performance on 60-240 seconds and >240 seconds exercise bouts.

Although BA appears to improve exercise performance, the long-term safety of BA has only been partially explored. Currently, the only known side effect of BA is unpleasant symptoms of parasthesia reported after consumption of large dosages; however, this can be minimized through consumption of smaller dosages throughout the day ¹⁷⁹⁾. While BA appears to be relatively safe in the short-term, the long-term safety is unknown. In cats, an addition of 5 percent BA to drinking water for 20 weeks has been shown to deplete taurine and result in damage to the brain; however, taurine is an essential amino acid for cats but not for humans and it is unknown if the smaller dosages consumed by humans could result in similar effects ¹⁸⁰⁾. BA may increase exercise performance and increase lean mass in bodybuilders and currently appears to be safe; however, studies are needed to determine the long-term safety of BA consumption.

Beta-hydroxy-beta-methylbutyrate

Beta-hydroxy-beta-methylbutyrate (HMB) is a metabolite of the amino acid leucine that has been shown to decrease muscle protein catabolism and increase muscle protein synthesis ¹⁸¹⁾, ¹⁸²⁾. The safety of HMB supplementation has been widely studied and no adverse effects on liver enzymes, kidney function, cholesterol, white blood cells, hemoglobin, or blood glucose have been observed ¹⁸³⁾, ¹⁸⁴⁾. Furthermore, two meta-analyses on HMB supplementation have concluded that HMB is safe and does not result in any major side effects ¹⁸⁵⁾. HMB may actually decrease blood pressure, total and LDL cholesterol, especially in hypercholesterolemic individuals.

HMB is particularly effective in catabolic populations such as the elderly and patients with chronic disease ¹⁸⁶⁾. However, studies on the effectiveness of HMB in trained, non-calorically restricted populations have been mixed. Reasons for discrepancies in the results of HMB supplementation studies in healthy populations may be due to many factors including clustering of data in these meta-analysis to include many studies from similar groups, poorly designed, non-periodized training protocols, small sample sizes, and lack of specificity between training and testing conditions ¹⁸⁷⁾. However, as a whole HMB appears to be effective in a majority of studies with longer-duration, more intense, periodized training protocols and may be beneficial to bodybuilders, particularly during planned over-reaching phases of training ¹⁸⁸⁾. While the authors hypothesize that HMB may be effective in periods of increased catabolism, such as during contest preparation, the efficacy of HMB on maintenance of lean mass in dieting athletes has not been investigated in a long-term study. Therefore, future studies are needed to determine the effectiveness of HMB during caloric restriction in healthy, lean, trained athletes.

Creatine

Creatine is a naturally-occurring amino acid (protein building block) that’s found in meat and fish, and also made by the human body predominately in the liver, kidneys, and to a lesser extent in the pancreas ¹⁸⁹⁾. Creatine is produced in your body at an amount of about 1 g/day ¹⁹⁰⁾. The remainder of the creatine available to the body is obtained through the diet at about 1 g/day for an omnivorous diet ¹⁹¹⁾. 95% of the bodies creatine stores are found in the skeletal muscle and the remaining 5% is distributed in the brain, liver, kidney, and testes ¹⁹²⁾.

Creatine is chemically known as a non-protein nitrogen; a compound which contains nitrogen but is not a protein per se ¹⁹³⁾. It is synthesized in the liver and pancreas from the amino acids arginine, glycine, and methionine ¹⁹⁴⁾, ¹⁹⁵⁾. Approximately 95% of the body’s creatine is stored in skeletal muscle. Additionally, small amounts of creatine are also found in the brain and testes ¹⁹⁶⁾, ¹⁹⁷⁾. About two thirds of the creatine found in skeletal muscle is stored as phosphocreatine (PCr) while the remaining amount of creatine is stored as free creatine ¹⁹⁸⁾. The total creatine pool (PCr + free creatine) in skeletal muscle averages about 120-140 grams for a 70 kg individual ¹⁹⁹⁾, depending on the skeletal muscle fiber type ²⁰⁰⁾ and quantity of muscle mass ²⁰¹⁾. However, the average human has the capacity to store up to 160 grams of creatine under certain conditions ²⁰²⁾, ²⁰³⁾. The body breaks down about 1 – 2% of the creatine pool per day (about 1–2 grams/day) into creatinine in the skeletal muscle ²⁰⁴⁾. The body production and dietary intake matches the rate of creatinine production from the degradation of phosphocreatine and creatine at 2.6% and 1.1%/d respectively. In general, oral creatine supplementation leads to an increase of creatine levels within the body. Creatine can be cleared from the blood by saturation into various organs and cells or by renal filtration then excreted in urine ²⁰⁵⁾.

Creatine stores can be replenished by obtaining creatine in the diet or through endogenous synthesis of creatine from glycine, arginine, and methionine ²⁰⁶⁾, ²⁰⁷⁾. Dietary sources of creatine include meats and fish. Large amounts of fish and meat must be consumed in order to obtain gram quantities of creatine. Whereas dietary supplementation of creatine provides an inexpensive and efficient means of increasing dietary availability of creatine without excessive fat and/or protein intake.

Three amino acids (glycine, arginine and methionine) and three enzymes (L-arginine:glycine amidinotransferase, guanidinoacetate methyltransferase and methionine adenosyltransferase) are required for creatine synthesis. The impact creatine synthesis has on glycine metabolism in adults is low, however the demand is more appreciable on the metabolism of arginine and methionine ²⁰⁸⁾.

As creatine is predominately present in the diet from meats, vegetarians have lower resting creatine concentrations ²⁰⁹⁾. It is converted into creatine phosphate or phosphocreatine and stored in the muscles, where it is used for energy ²¹⁰⁾. During high-intensity, short-duration exercise, such as lifting weights or sprinting, phosphocreatine is converted into ATP, a major source of energy within the human body.

Biochemically speaking, the energy supplied to rephosphorylate adenosine diphosphate (ADP) to adenosine triphosphate (ATP) during and following intense exercise is largely dependent on the amount of phosphocreatine (PCr) stored in the muscle ²¹¹⁾, ²¹²⁾. As phosphocreatine stores become depleted during intense exercise, energy availability diminishes due to the inability to resynthesize ATP at the rate required to sustained high-intensity exercise ²¹³⁾, ²¹⁴⁾. Consequently, the ability to maintain maximal-effort exercise declines. The availability of phosphocreatine in the muscle may significantly influence the amount of energy generated during brief periods of high-intensity exercise. Furthermore, it has been hypothesized that increasing muscle creatine content, via creatine supplementation, may increase the availability of phosphocreatine allowing for an accelerated rate of resynthesis of ATP during and following high-intensity, short-duration exercise ²¹⁵⁾, ²¹⁶⁾. Theoretically, creatine supplementation during training may lead to greater training adaptations due to an enhanced quality and volume of work performed. In terms of potential medical applications, creatine is intimately involved in a number of metabolic pathways. For this reason, medical researchers have been investigating the potential therapeutic role of creatine supplementation in a variety of patient populations.

Creatine supplements are popular among body builders and competitive athletes. As an oral supplement, the most widely used and researched form is creatine monohydrate ²¹⁷⁾. When orally ingested, creatine monohydrate has shown to improve exercise performance and increase fat free mass ²¹⁸⁾, ²¹⁹⁾, ²²⁰⁾, ²²¹⁾, ²²²⁾. The attraction of creatine is that it may increase lean muscle mass and enhance athletic performance, particularly during high-intensity, short-duration sports (like high jumping and weight lifting).

However, not all human studies show that creatine improves athletic performance ²²³⁾. Nor does every person seem to respond the same way to creatine supplements. For example, people who tend to have naturally high stores of creatine in their muscles don’t get an energy-boosting effect from extra creatine. Preliminary clinical studies also suggest that creatine’s ability to increase muscle mass and strength may help fight muscle weakness associated with illnesses, such as heart failure and muscular dystrophy.

Creatine supplementation Responders vs. Non-responders

Syrotuik and Bell ²²⁴⁾ investigated the physical characteristics of responder and non-responder subjects to creatine supplementation in recreationally resistance trained men with no history of creatine monohydrate usage. The supplement group was asked to ingest a loading dosage of 0.3 g/kg/d for 5 days. The physiological characteristics of responders were classified using Greenhaff et al ²²⁵⁾ criterion of >20 mmol/kg dry weight increase in total intramuscular creatine and phosphocreatine and non responders as <10 mmol/kg dry weight increase, a third group labeled quasi responders were also used to classify participants who fell in between the previously mentioned groups (10-20 mmol/kg dry weight). Overall, the supplemented group showed a mean increase in total resting muscle creatine and phosphocreatine of 14.5% (from 111.12 ± 8.87 mmol/kg dry weight to 127.30 ± 9.69 mmol/kg dry weight) whilst the placebo group remained relatively unaffected (from 115.70 ± 14.99 mmol/kg dry weight to 111.74 ± 12.95 mmol/kg dry weight). However when looking at individual cases from the creatine group the results showed a variance in response. From the 11 males in the supplemented group, 3 participants were responders (mean increase of 29.5 mmol/kg dry weight or 27%), 5 quasi responders (mean increase of 14.9 mmol/kg dry weight or 13.6%) and 3 non-responders (mean increase of 5.1 mmol/kg dry weight or 4.8%). Using muscle biopsies of the vastus lateralis, a descending trend for groups and mean percentage fiber type was observed. Responders showed the greatest percentage of type II fibers followed by quasi responders and non-responders. The responder and quasi responder groups had an initial larger cross sectional area for type I, type IIa and type IIx fibers. The responder group also had the greatest mean increase in the cross sectional area of all the muscle fiber types measured (type I, type IIa and type IIx increased 320, 971 and 840 μm2 respectively) and non-responders the least (type I, type IIa and type IIx increased 60, 46 and 78 μm2 respectively). There was evidence of a descending trend for responders to have the highest percentage of type II fibers; furthermore, responders and quasi responders possessed the largest initial cross sectional area of type I, IIa and IIx fibers. Responders were seen to have the lowest initial levels of creatine and phosphocreatine. This has also been observed in a previous study ²²⁶⁾ which found that subjects whose creatine levels were around 150 mmol/Kg dry mass did not have any increments in their creatine saturation due to creatine supplementation, neither did they experience any increases of creatine uptake, phosphocreatine resynthesis and performance. This would indicate a limit maximum size of the creatine pool.

In summary responders are those individuals with a lower initial level of total muscle creatine content, greater population of type II fibers and possess higher potential to improve performance in response to creatine supplementation.

Effects of creatine supplementation on Muscle Mass

Cribb et al (2007) ²²⁷⁾ observed greater improvements on 1RM, lean body mass, fiber cross sectional area and contractile protein in trained young males when resistance training was combined with a multi-nutrient supplement containing 0.1 g/kg/d of creatine, 1.5 g/kg/d of protein and carbohydrate compared with protein alone or a protein carbohydrate supplement without the creatine. These findings were novel because at the time no other research had noted such improvements in body composition at the cellular and sub cellular level in resistance trained participants supplementing with creatine. The amount of creatine consumed in the study by Cribb et al ²²⁸⁾ was greater than the amount typically reported in previous studies (a loading dose of around 20 g/d followed by a maintenance dose of 3-5 g/d is generally equivalent to approximately 0.3 g/kg/d and 0.03 g/kg/d respectively) and the length of the supplementation period or absence of resistance exercise may explain the observed transcriptional level changes that were absent in previous studies ²²⁹⁾, ²³⁰⁾.

Deldicque et al ²³¹⁾ found a 250%, 45% and 70% increase for collagen mRNA, glucose transporter 4 (GLUT4) and Myosin heavy chain IIA, respectively after 5 days creatine loading protocol (21 g/d). The authors speculated that creatine in addition to a single bout of resistance training can favor an anabolic environment by inducing changes in gene expression after only 5 days of supplementation.

When creatine supplementation is combined with heavy resistance training, muscle insulin like growth factor (IGF-1) concentration has been shown to increase. Burke et al ²³²⁾ examined the effects of an 8 week heavy resistance training protocol combined with a 7 day creatine loading protocol (0.25 g/d/kg lean body mass) followed by a 49 day maintenance phase (0.06 g/kg lean mass) in a group of vegetarian and non-vegetarian, novice, resistance trained men and women. Compared to placebo, creatine groups produced greater increments in IGF-1 (78% Vs 55%) and body mass (2.2 Vs 0.6 kg). Additionally, vegetarians within the supplemented group had the largest increase of lean mass compared to non vegetarian (2.4 and 1.9 kg respectively). Changes in lean mass were positively correlated to the modifications in intramuscular total creatine stores which were also correlated with the modified levels of intramuscular IGF-1. The authors suggested that the rise in muscle IGF-1 content in the creatine group could be due to the higher metabolic demand created by a more intensely performed training session. These amplifying effects could be caused by the increased total creatine store in working muscles. Even though vegetarians had a greater increase in high energy phosphate content, the IGF-1 levels were similar to the amount observed in the non vegetarian groups. These findings do not support the observed correlation pattern by which a low essential amino acid content of a typical vegetarian diet should reduce IGF-1 production ²³³⁾. According to authors opinions it is possible that the addition of creatine and subsequent increase in total creatine and phosphocreatine storage might have directly or indirectly stimulated production of muscle IGF-I and muscle protein synthesis, leading to an increased muscle hypertrophy ²³⁴⁾.

Effects of creatine ingestion to improve recovery from injury, muscle damage and oxidative stress induced by exercise

Creatine supplementation may also be of benefit to injured athletes. Op’t Eijnde et al ²³⁵⁾ noted that the expected decline in GLUT4 content after being observed during a immobilization period can be offset by a common loading creatine (20g/d) supplementation protocol. In addition, combining creatine monohydrate 15g/d for 3 weeks following 5 g/d for the following 7 weeks positively enhances GLUT4 content, glycogen, and total muscle creatine storage ²³⁶⁾.

Bassit et al (Bassit RA, Pinheiro CH, Vitzel KF, Sproesser AJ, Silveira LR, Curi R. Effect of short-term creatine supplementation on markers of skeletal muscle damage after strenuous contractile activity. Eur J Appl Physiol. 2010;108:945–955. doi: 10.1007/s00421-009-1305-1. https://www.ncbi.nlm.nih.gov/pubmed/19956970()) observed a decrease in several markers of muscle damage (creatine kinase, lactate dehydrogenase, aldolase, glutamic oxaloacetic acid transaminase and glutamic pyruvic acid transaminase) in 4 athletes after an iron man competition who supplemented with 20 g/d plus 50 g maltodextrin during a 5 day period prior to the competition.

Cooke et al ²³⁷⁾ observed positive effects of a prior (0.3 g/d kg body weight) loading and a post maintenance protocol (0.1 g/d kg body weight) to attenuate the loss of strength and muscle damage after an acute supramaximal (3 set x 10 rep with 120% 1RM) eccentric resistance training session in young males. The authors speculate that creatine ingestion prior to exercise may enhance calcium buffering capacity of the muscle and reduce calcium-activated proteases which in turn minimize sarcolemma and further influxes of calcium into the muscle. In addition creatine ingestion post exercise would enhance regenerative responses, favoring a more anabolic environment to avoid severe muscle damage and improve the recovery process. In addition, in vitro studies have demonstrated the antioxidant effects of creatine to remove superoxide anion radicals and peroxinitrite radicals ²³⁸⁾. This antioxidant effect of creatine has been associated with the presence of Arginine in its molecule. Arginine is also a substrate for nitric oxide synthesis and can increase the production of nitric oxide which has higher vasodilatation properties, and acts as a free radical that modulates metabolism, contractibility and glucose uptake in skeletal muscle. Other amino acids contained in the creatine molecule such as glycine and methinine may be especially susceptible to free radical oxidation because of sulfhydryl groups ²³⁹⁾. A more recent in vitro study showed that creatine exerts direct antioxidant activity via a scavenging mechanism in oxidatively injured cultured mammalian cells ²⁴⁰⁾. In a recent in vivo study Rhaini et al ²⁴¹⁾ showed a positive effect of 7 days of creatine supplementation (4 x 5 g CM 20 g total) on 27 recreational resistance trained males to attenuate the oxidation of DNA and lipid peroxidation after a strenuous resistance training protocol.

Collectively the above investigations indicate that creatine supplementation can be an effective strategy to maintain total creatine pool during a rehabilitation period after injury as well as to attenuate muscle damage induced by a prolonged endurance training session. In addition, it seems that creatine can act as an effective antioxidant agent after more intense resistance training sessions ²⁴²⁾.

Effects of creatine supplementation on glycogen stores

It is suggested ²⁴³⁾, ²⁴⁴⁾ that another mechanism for the effect of creatine could be enhanced muscle glycogen accumulation and GLUT4 expression, when creatine supplementation is combined with a glycogen depleting exercise. Whereas it has been observed ²⁴⁵⁾ that creatine supplementation alone does not enhance muscle glycogen storage. Hickner et al ²⁴⁶⁾ observed positive effects of creatine supplementation for enhancing initial and maintaining a higher level of muscle glycogen during 2 hours of cycling. In general, it is accepted that glycogen depleting exercises, such as high intensity or long duration exercise should combine high carbohydrate diets with creatine supplementation to achieve heightened muscle glycogen stores ²⁴⁷⁾.

Effects of creatine supplementation on predominantly aerobic exercise

Although creatine supplementation has been shown to be more effective on predominantly anaerobic intermittent exercise, there is some evidence of its positive effects on endurance activities. Branch ²⁴⁸⁾ highlights that endurance activities lasting more than 150 seconds rely on oxidative phosphorylation as primary energy system supplier. From this meta analysis ²⁴⁹⁾, it would appear that the ergogenic potential for creatine supplementation on predominantly aerobic endurance exercise diminishes as the duration of the activity increases over 150s. However it is suggested that creatine supplementation may cause a change in substrate utilization during aerobic activity possibly leading to an increase in steady state endurance performance.

Chwalbinska-Monteta ²⁵⁰⁾ observed a significant decrease in blood lactate accumulation when exercising at lower intensities as well as an increase in lactate threshold in elite male endurance rowers after consuming a short loading (5 days 20 g/d) creatine monohydrate protocol. However, the effects of creatine supplementation on endurance performance have been questioned by some studies. Graef et al ²⁵¹⁾ examined the effects of four weeks of creatine citrate supplementation and high-intensity interval training on cardio respiratory fitness. A greater increase of the ventilatory threshold was observed in the creatine group respect to placebo; however, oxygen consumption showed no significant differences between the groups. The total work presented no interaction and no main effect for time for any of the groups. Thompson et al ²⁵²⁾ reported no effects of a 6 week 2 g creatine monohydrate/day in aerobic and anaerobic endurance performance in female swimmers.

Documented effects of creatine supplementation on physical performance

The majority of studies focusing on creatine supplementation report an increase in the body’s’ creatine pool ²⁵³⁾, ²⁵⁴⁾, ²⁵⁵⁾. There is a positive relationship between muscle creatine uptake and exercise performance ²⁵⁶⁾. Volek et al. ²⁵⁷⁾ observed a significant increase in strength performance after 12 weeks creatine supplementation with a concurrent periodized heavy resistance training protocol. The creatine supplementation protocol consisted of a weeklong loading period of 25 g/day followed by a 5 gram maintenance dose for the remainder of the training. These positive effects were attributed to an increased total creatine pool resulting in more rapid adenosine triphosphate (ATP) regeneration between resistance training sets allowing athletes to maintain a higher training intensity and improve the quality of the workouts along the entire training period.

It is regularly reported that creatine supplementation, when combined with heavy resistance training leads to enhanced physical performance, fat free mass, and muscle morphology ²⁵⁸⁾, ²⁵⁹⁾, ²⁶⁰⁾. A 2003 meta analysis ²⁶¹⁾ showed individuals ingesting creatine, combined with resistance training, obtain on average +8% and +14% more performance on maximum (1RM) or endurance strength (maximal repetitions at a given percent of 1RM) respectively than the placebo groups. However, contradicting studies have reported no effects of creatine supplementation on strength performance. Jakobi et al ²⁶²⁾ found no effects of a short term creatine loading protocol upon isometric elbow flexion force, muscle activation, and recovery process. However, this study did not clearly state if creatine supplementation was administered concurrent with resistance training. Bemben et al ²⁶³⁾ have shown no additional benefits of creatine alone or combined with whey protein for improving strength and muscle mass after a progressive 14 weeks (3 days per week) resistance training program in older men. These conflicting results can be explained by the possibility that the supplemented groups were formed by a greater amount of non-responders or even because creatine supplementation was administered on the training days only (3 times a week). This strategy has not been adequately tested as effective in middle aged and older men for maintaining post loading elevated creatine stores ²⁶⁴⁾.

A quantitative, comprehensive scientific summary and view of knowledge up to 2007 on the effects of creatine supplementation in athletes and active people was published in a 100 citation review position paper by the International Society of Sports Nutrition ²⁶⁵⁾. More recent literature has provided greater insight into the anabolic/performance enhancing mechanisms of creatine supplementation ²⁶⁶⁾, ²⁶⁷⁾ suggesting that these effects may be due to satellite cell proliferation, myogenic transcription factors and insulin-like growth factor-1 signalling ²⁶⁸⁾. Saremi et al ²⁶⁹⁾ reported a change in myogenic transcription factors when creatine supplementation and resistance training are combined in young healthy males. It was found that serum levels of myostatin, a muscle growth inhibitor, were decreased in the creatine group.

Collectively, in spite of a few controversial results, it seems that creatine supplementation combined with resistance training would amplify performance enhancement on maximum and endurance strength as well muscle hypertrophy ²⁷⁰⁾.

Effects of creatine supplementation on predominantly anaerobic exercise

Creatine has demonstrated neuromuscular performance enhancing properties on short duration, predominantly anaerobic, intermittent exercises. Bazzucch et al ²⁷¹⁾ observed enhanced neuromuscular function of the elbow flexors in both electrically induced and voluntary contractions but not on endurance performance after 4 loading doses of 5 g creatine plus 15 g maltodextrin for 5/d in young, moderately trained men. Creatine supplementation may facilitate the reuptake of Ca2+ into the sacroplasmic reticulum by the action of the Ca2+ adenosine triphosphatase pump, which could enable force to be produced more rapidly through the faster detachment of the actomyosin bridges.

A previous meta-analysis ²⁷²⁾ reported an overall creatine supplementation effect size (ES) of 0.24 ± 0.02 for activities lasting ≤30 s. (primarily using the ATP- phosphocreatine energy system). For this short high-intensity exercise, creatine supplementation resulted in a 7.5 ± 0.7% increase from base line which was greater than the 4.3 ± 0.6% improvement observed for placebo groups. When looking at the individual selected measures for anaerobic performance the greatest effect of creatine supplementation was observed on the number of repetitions which showed an ES of 0.64 ± 0.18. Furthermore, an increase from base line of 45.4 ± 7.2% compared to 22.9 ± 7.3% for the placebo group was observed. The second greatest ES was on the weight lifted at 0.51 ± 0.16 with an increase from base line of 13.4 ± 2.7% for the placebo group and 24.7 ± 3.9% for the creatine group. Other measures improved by creatine with a mean ES greater than 0 were for the amount of work accomplished, weight lifted, time, force production, cycle ergometer revolutions/min and power. The possible effect of creatine supplementation on multiple high intensity short duration bouts (<30 s) have shown an ES not statistically significant from 0. This would indicate that creatine supplementation might be useful to attenuate fatigue symptoms over multiple bouts of high-intensity, short duration exercise. The ES of creatine on anaerobic endurance exercise (>30 – 150s), primarily using the anaerobic glycolysis energy system, was 0.19 ± 0.05 with an improvement from baseline of 4.9 ± 1.5 % for creatine and -2.0 ± 0.6% for the placebo. The specific aspects of anaerobic endurance performance improved by creatine supplementation were work and power, both of which had a mean ES greater than 0. From the findings of this previous meta-analysis ²⁷³⁾ it would appear that creatine supplementation has the most pronounced effect on short duration (<30s) high intensity intermittent exercises.

Effects of creatine supplementation on predominantly aerobic exercise

Although creatine supplementation has been shown to be more effective on predominantly anaerobic intermittent exercise, there is some evidence of its positive effects on endurance activities. Branch ²⁷⁴⁾ highlights that endurance activities lasting more than 150 seconds rely on oxidative phosphorylation as primary energy system supplier. From this meta analysis ²⁷⁵⁾, it would appear that the ergogenic potential for creatine supplementation on predominantly aerobic endurance exercise diminishes as the duration of the activity increases over 150s. However it is suggested that creatine supplementation may cause a change in substrate utilization during aerobic activity possibly leading to an increase in steady state endurance performance.

Chwalbinska-Monteta ²⁷⁶⁾ observed a significant decrease in blood lactate accumulation when exercising at lower intensities as well as an increase in lactate threshold in elite male endurance rowers after consuming a short loading (5 days 20 g/d) CM protocol. However, the effects of creatine supplementation on endurance performance have been questioned by some studies. Graef et al ²⁷⁷⁾ examined the effects of four weeks of creatine citrate supplementation and high-intensity interval training on cardio respiratory fitness. A greater increase of the ventilatory threshold was observed in the creatine group respect to placebo; however, oxygen consumption showed no significant differences between the groups. The total work presented no interaction and no main effect for time for any of the groups. Thompson et al ²⁷⁸⁾ reported no effects of a 6 week 2 g CM/d in aerobic and anaerobic endurance performance in female swimmers. In addition, of the concern related to the dosage used in these studies, it could be possible that the potential benefits of creatine supplementation on endurance performance were more related to effects of anaerobic threshold localization.

Effects of creatine supplementation on range of motion

Sculthorpe et al ²⁷⁹⁾ has shown that a 5 day (25g/d) loading protocol of creatine supplementation followed by a further 3 days of 5 g/d negatively influence both active ankle dorsiflexion and shoulder abduction and extension range of movement (ROM) in young men. There are two possible theories to explain these effects: 1) Creatine supplementation increases intracellular water content resulting in increased muscle stiffness and resistance to stretch; 2) Neural outflow from the muscle spindles is affected due to an increased volume of the muscle cell. The authors highlight that the active ROM measures were taken immediately after the loading phase and the reduced active ROM may not be seen after several weeks of maintenance phase ²⁸⁰⁾. Hile et al ²⁸¹⁾ observed an increase in compartment pressure in the anterior compartment of the lower leg, which may also have been responsible for a reduced active ROM.

Creatine use in children and adolescents

Creatine supplementation in the under 18 population has not received a great deal of attention, especially in regards to sports/exercise performance. Despite this, creatine is being supplemented in young, <18 years old, athletes ²⁸²⁾, ²⁸³⁾. In a 2001 report ²⁸⁴⁾ conducted on pupils from middle and high school (aged 10 – 18) in Westchester County (USA) 62 of the 1103 pupils surveyed were using creatine. The authors found this concerning for 2 main reasons: firstly, the safety of creatine supplementation is not established for this age group and is therefore not recommended. Secondly, it was speculated that taking creatine would lead on to more dangerous performance enhancing products such as anabolic steroids. It is important to point out that this potential escalation is speculation. Furthermore, a questionnaire was used to determine creatine use amongst this age group and does not necessarily reflect the truth.

A child’s ability to regenerate high energy phosphates during high intensity exercise is less than that of an adult. Due to this, creatine supplementation may benefit the rate and use of creatine phosphate and ATP rephosporylation. However, performance in short duration high-intensity exercise can be improved through training therefore supplementation may not be necessary ²⁸⁵⁾.

Based on the limited data on performance and safety, some authors have not identified any conclusions and do not recommend its consumption in regards to creatine supplementation in children and adolescents ²⁸⁶⁾, ²⁸⁷⁾. Conversely, according to the view of the International Society of Sports Nutrition ²⁸⁸⁾, younger athletes should consider a creatine supplement under certain conditions: puberty is past and he/she is involved in serious competitive training; the athlete is eating a well-balanced caloric adequate diet; he/she as well as the parents approve and understand the truth concerning the effects of creatine supplementation; supplement protocols are supervised by qualified professionals; recommended doses must not be exceeded; quality supplements are administered.

Within this framework, creatine supplementation in young, post puberty athletes can be considered a high quality type of “food” that can offer additional benefits to optimise training outcomes.

Safety and side effects of creatine supplementation

There have been a few reported renal health disorders associated with creatine supplementation ²⁸⁹⁾, ²⁹⁰⁾. These are isolated reports in which recommended dosages are not followed or there is a history of previous health complaints, such as renal disease or those taking nephrotoxic medication aggravated by creatine supplementation ²⁹¹⁾. Specific studies into creatine supplementation, renal function and/or safety conclude that although creatine does slightly raise creatinine levels there is no progressive effect to cause negative consequences to renal function and health in already healthy individuals when proper dosage recommendations are followed ²⁹²⁾, ²⁹³⁾, ²⁹⁴⁾, ²⁹⁵⁾. Urinary methylamine and formaldehyde have been shown to increase due to creatine supplementation of 20 g/d; this however did not bring the production outside of normal healthy range and did not impact on kidney function ²⁹⁶⁾, ²⁹⁷⁾. It has been advised that further research be carried out into the effects of creatine supplementation and health in the elderly and adolescent ²⁹⁸⁾, ²⁹⁹⁾. More recently, a randomized, double blind, 6 month resistance exercise and supplementation intervention ³⁰⁰⁾ was performed on elderly men and women (age >65 years) in which subjects were assigned to either a supplement or placebo group. The supplement group was given 5 g creatine monohydrate, 2 g dextrose and 6 g conjugated linoleic acid/d, whilst the placebo group consumed 7 g dextrose and 6 g safflower oil/d. Creatine monohydrate administration showed significantly greater effects to improve muscular endurance, isokinetic knee extension strength, fat free mass and to reduce fat mass compared to placebo. Furthermore the supplement group had an increase in serum creatinine but not creatinine clearance suggesting no negative effect on renal function.

Cornelissen et al ³⁰¹⁾ analyzed the effects of 1 week loading protocol (3 X 5 g/d creatine monohydrate) followed by a 3 month maintenance period (5 g/d) on cardiac patients involved in an endurance and resistance training program. Although creatine monohydrate supplementation did not significantly enhance performance, markers of renal and liver function were within normal ranges indicating the safety of the applied creatine supplementation protocol.

A retrospective study ³⁰²⁾, that examined the effects of long lasting (0.8 to 4 years) creatine monohydrate supplementation on health markers and prescribed training benefits, suggested that there is no negative health effects (including muscle cramp or injuries) caused by long term creatine monohydrate consumption. In addition, despite many anecdotal claims, it appears that creatine supplementation would have positive influences on muscle cramps and dehydration ³⁰³⁾. Creatine was found to increase total body water possibly by decreasing the risk of dehydration, reducing sweat rate, lowering core body temperature and exercising heart rate. Furthermore, creatine supplementation does not increase symptoms nor negatively affect hydration or thermoregulation status of athletes exercising in the heat ³⁰⁴⁾, ³⁰⁵⁾. Additionally, CM ingestion has been shown to reduce the rate of perceived exertion when training in the heat ³⁰⁶⁾.

It is prudent to note that creatine supplementation has been shown to reduce the body’s endogenous production of creatine, however levels return to normal after a brief period of time when supplementation ceases ³⁰⁷⁾, ³⁰⁸⁾. Despite this creatine supplementation has not been studied/supplemented with for a relatively long period. Due to this, long term effects are unknown, therefore safety cannot be guaranteed. Whilst the long term effects of creatine supplementation remain unclear, no definitive certainty of either a negative or a positive effect upon the body has been determined for many health professionals and national agencies ³⁰⁹⁾, ³¹⁰⁾. For example the French Sanitary Agency has banned the buying of creatine due to the unproven allegation that a potential effect of creatine supplementation could be that of mutagenicity and carcinogenicity from the production of heterocyclic amines ³¹¹⁾. Long term and epidemiological data should continue to be produced and collected to determine the safety of creatine in all healthy individuals under all conditions ³¹²⁾.

Commercially available forms of creatine supplements

There are several different available forms of creatine: creatine anhydrous which is creatine with the water molecule removed in order to increase the concentration of creatine to a greater amount than that found in creatine monohydrate. Creatine has been manufactured in salt form: creatine pyruvate, creatine citrate, creatine malate, creatine phosphate, magnesium creatine, creatine oroate, Kre Alkalyn (creatine with baking soda). Creatine can also be manufactured in an ester form. Creatine ethyl ester (hydrochloride) is an example of this, as is creatine gluconate which is creatine bound to glucose. Another form is creatine effervescent which is creatine citrate or creatine monohydrate with citric acid and bicarbonate. The citric acid and bicarbonate react to produce an effervescent effect. When mixed with water the creatine separates from its carrier leaving a neutrally charged creatine, allowing it to dissolve to a higher degree in water. Manufacturers claim that creatine effervescent has a longer and more stable life in solution. When di-creatine citrate effervescent was studied ³¹³⁾ for stability in solution it was found that the di-creatine citrate dissociates to citric acid and creatine in aqueous solutions which in turn forms creatine monohydrate and eventually crystallises out of the solution due to its low solubility. Some of the creatine may also convert to creatinine.

Jager et al ³¹⁴⁾ observed 1.17 and 1.29 greater peak plasma creatine concentration 1 hour after ingesting creatine pyruvate compared to isomolar amount of creatine monohydrate and creatine citrate respectively. However time to peak concentration, and velocity constants of absorption and elimination, was the same for all three forms of creatine. Although not measured in this study it is questionable that these small differences in plasma creatine concentrations would have any effect on the increase of muscle creatine uptake. Jäger et al ³¹⁵⁾ investigated the effects of 28-days of creatine pyruvate and citrate supplementation on endurance capacity and power measured during an intermittent handgrip (15 seconds effort per 45 seconds rest) exercise in healthy young athletes. The authors used a daily dose protocol with the intention to slowly saturate muscle creatine stores. Both forms of creatine showed slightly different effects on plasma creatine absorption and kinetics. The two creatine salts significantly increased mean power but only pyruvate forms showed significant effects for increasing force and attenuating fatigability during all intervals. These effects can be attributed to an enhanced contraction and relaxation velocity as well as a higher blood flow and muscle oxygen uptake. On the other hand, the power performance measured with the citrate forms decreases with time and improvements were not significant during the later intervals. In spite of these positive trends further research is required about the effects of these forms of creatine as there is little or no evidence for their safety and efficacy. Furthermore the regularity status of the novel forms of creatine vary from country to country and are often found to be unclear when compared to that of creatine monohydrate ³¹⁶⁾.

In summary, creatine salts have been show to be less stable than creatine monohydrate. However the addition of carbohydrates could increase their stability ³¹⁷⁾. The potential advantages of creatine salts over creatine monohydrate include enhanced aqueous solubility and bioavailability which would reduce their possible gastrointestinal adverse effects ³¹⁸⁾. The possibility for new additional formulation such as tablets or capsules is interesting for its therapeutic application due to its attributed better dissolution kinetics and oral absorption compared to creatine monohydrate ³¹⁹⁾. However more complete in vivo pharmaceutical analysis of creatine salts are required to fully elucidate their potential advantages/disadvantages over the currently available supplement formulations.

Creatine is a hydrophilic polar molecule that consists of a negatively charged carboxyl group and a positively charged functional group ³²⁰⁾. The hydrophilic nature of creatine limits its bioavailability [65]. In an attempt to increase creatines bioavailability creatine has been esterified to reduce the hydrophilicity; this product is known as creatine ethyl ester. Manufacturers of creatine ethyl ester promote their product as being able to by-pass the creatine transporter due to improved sarcolemmal permeability toward creatine ³²¹⁾. Spillane et al ³²²⁾ analyzed the effects of a 5 days loading protocol (0.30 g/kg lean mass) followed by a 42 days maintenance phase (0.075 g/kg lean mass) of CM or ethyl ester both combined with a resistance training program in 30 novice males with no previous resistance training experience. The results of this study ³²³⁾ showed that ethyl ester was not as effective as creatine monohydrate to enhance serum and muscle creatine stores. Furthermore creatine ethyl ester offered no additional benefit for improving body composition, muscle mass, strength, and power. This research did not support the claims of the creatine ethyl ester manufacturers.

Polyethylene glycol is a non-toxic, water-soluble polymer that is capable of enhancing the absorption of creatine and various other substances ³²⁴⁾. Polyethylene glycol can be bound with creatine monohydrate to form polyethylene glycosylated creatine. One study ³²⁵⁾ found that 5 g/d for 28 days of polyethylene glycosylated creatine was capable of increasing 1RM bench press in 22 untrained young men but not for lower body strength or muscular power. Body weight also did not significantly change in the creatine group which may be of particular interest to athletes in weight categories that require upper body strength. Herda et al ³²⁶⁾ analyzed the effects of 5 g of creatine monohydrate and two smaller doses of polyethylene glycosylated creatine (containing 1.25 g and 2.5 g of creatine) administered over 30 days on muscular strength, endurance, and power output in fifty-eight healthy men. Creatine monohydrate produced a significantly greater improvement in mean power and body weight meanwhile both creatine monohydrate and polyethylene glycosylated form showed a significantly greater improvement for strength when compared with control group. These strength increases were similar even though the dose of creatine in the polyethylene glycosylated creatine groups was up to 75% less than that of creatine monohydrate. These results seem to indicate that the addition of polyethylene glycol could increase the absorption efficiency of creatine but further research is needed before a definitive recommendation can be reached.

Creatine in combination with other supplements

Although creatine can be bought commercially as a standalone product it is often found in combination with other nutrients. A prime example is the combination of creatine with carbohydrate or protein and carbohydrate for augmenting creatine muscle retention ³²⁷⁾ mediated through an insulin response from the pancreas ³²⁸⁾. Steenge et al ³²⁹⁾ found that body creatine retention of 5 g CM was increased by 25% with the addition of 50 g of protein and 47 g of carbohydrate or 96 g carbohydrate when compared to a placebo treatment of 5 g carbohydrate. The addition of 10g of creatine to 75 g of dextrose, 2 g of taurine, vitamins and minerals, induced a change in cellular osmolarity which in addition to the expected increase in body mass, seems to produce an up regulation of large scale gene expression (mRNA content of genes and protein content of kinases involved in osmosensing and signal transduction, cytoskeleton remodelling, protein and glycogen synthesis regulation, satellite cell proliferation and differentiation, DNA replication and repair, RNA transcription control, and cell survival) ³³⁰⁾. Similar findings have also been reported for creatine monohydrate supplementation alone when combined with resistance training ³³¹⁾.

A commercially available pre-workout formula comprised of 2.05 g of caffeine, taurine and glucuronolactone, 7.9 g of L-leucine, L-valine, L-arginine and L-glutamine, 5 g of di-creatine citrate and 2.5 g of β-alanine mixed with 500 ml of water taken 10 minutes prior to exercise has been shown to enhance time to exhaustion during moderate intensity endurance exercise and to increase feelings of focus, energy and reduce subjective feelings of fatigue before and during endurance exercise due to a synergistic effect of the before mentioned ingredients ³³²⁾. The role of creatine in this formulation is to provide a neuroprotective function by enhancing the energy metabolism in the brain tissue, promoting antioxidant activities, improving cerebral vasculation and protecting the brain from hyperosmotic shock by acting as a brain cell osmolyte. Creatine can provide other neuroprotective benefits through stabilisation of mitochondrial membranes, stimulation of glutamate uptake into synaptic vesicles and balance of intracellular calcium homeostasis ³³³⁾.

Summary

The above review indicates that creatine supplementation has positive effects on:

• Amplifying the effects of resistance training for enhancing strength and muscle mass.
• Improving the quality and benefits of high intensity intermittent speed training.
• Improving aerobic endurance performance in trials lasting more than 150s.
• Seems to produce positive effects on strength, power, fat free mass, daily living performance and neurological function in young and older people.
• Regarding predominantly aerobic endurance performance, the increased bodies’ creatine stores, seems to amplify favorable physiological adaptations such as: increased plasma volume, glycogen storage, improvements of ventilatory threshold and a possible reduction of oxygen consumption in sub maximal exercise.

A typical creatine supplementation protocol of either a loading phase of 20 to 25 g CM/d or 0.3 g CM/kg/d split into 4 to 5 daily intakes of 5 g each have been recommended to quickly saturate creatine stores in the skeletal muscle. However a more moderate protocol where several smaller doses of creatine are ingested along the day (20 intakes of 1 g every 30 min) could be a better approach to get a maximal saturation of the intramuscular creatine store. In order to keep the maximal saturation of body creatine, the loading phase must be followed by a maintenance period of 3-5 g CM/d or 0.03 g CM/kg/d. These strategies appear to be the most efficient way of saturating the muscles and benefitting from CM supplementation. However more recent research has shown CM supplementation at doses of 0.1 g/kg body weight combined with resistance training improves training adaptations at a cellular and sub-cellular level. Creatine retention by the body from supplementation appears to be promoted by about 25% from the simultaneous ingestion of carbohydrate and/or protein mediated through an increase in insulin secretion. This combination would produce a faster saturation rate but has not been shown to have a greater effect on performance.

The available evidence indicates that creatine consumption is safe. This perception of safety cannot be guaranteed especially that of the long term safety of creatine supplementation and the various forms of creatine which are administered to different populations (athletes, sedentary, patient, active, young or elderly) throughout the world.

Branched-Chain Amino Acid Supplement

It is well-established that ingestion of essential amino acids following resistance exercise stimulates an increased response of muscle protein synthesis (MPS) in humans ³³⁴⁾, ³³⁵⁾, ³³⁶⁾. Indeed, the stimulation of muscle protein synthesis in humans can be achieved by supplying essential amino acids only (i.e., the non-EAAs necessary for MPS may be supplied by endogenous sources) ³³⁷⁾. More recent evidence from studies in rodents and cell culture models suggest that the stimulation of muscle protein synthesis by essential amino acids may be mediated by a few amino acids rather than a combination of all essential amino acids ³³⁸⁾. The branched-chain amino acid (BCAA), leucine, has been shown to play a unique role in stimulating MPS ³³⁹⁾. Leucine serves as substrate for the synthesis of new muscle proteins and as a signal to initiate the rate-limiting translation initiation step of muscle protein synthesis ³⁴⁰⁾. Accordingly, the response of MPS to leucine provision has been extensively investigated over the past two decades, both in cell culture studies and in vivo rodent and human ³⁴¹⁾ studies.

The stimulation of muscle protein synthesis is accompanied by an increased activation of intracellular signaling proteins that regulate the translational activity of muscle protein synthesis ³⁴²⁾. In particular, the mechanistic/mammalian target of rapamycin complex-1 (mTORC1) signaling, often assessed as the phosphorylation status of the ribosomal S6 protein kinase (S6K1), is stimulated by ingestion of EAA following resistance exercise ³⁴³⁾. There is current debate over whether leucine alone ³⁴⁴⁾, or the BCAAs combined ³⁴⁵⁾, provide the most important component of an exogenous EAA source for stimulating the mTORC1-S6K1 signaling pathway. Whereas, the inclusion of leucine is necessary for the maximal activation of mTORC1 signaling ³⁴⁶⁾, recent results from the same research group show that mTORC1 signaling is enhanced with the addition of the other two BCAAs, valine and isoleucine ³⁴⁷⁾. Moreover, there often is a disconnect between the response of mTORC1 signaling and muscle protein synthesis ³⁴⁸⁾, ³⁴⁹⁾. Thus, the response of MPS to BCAA ingestion is still uncertain.

Branched chain amino acids

Branched chain amino acids (BCAA’s) make up 14-18% of amino acids in skeletal muscle proteins and are quite possibly the most widely used supplements among natural bodybuilders ³⁵⁰⁾. Of the BCAA’s, leucine is of particular interest because it has been shown to stimulate protein synthesis to an equal extent as a mixture of all amino acids ³⁵¹⁾. However, ingestion of leucine alone can lead to depletion of plasma valine and isoleucine; therefore, all three amino acids need to be consumed to prevent plasma depletion of any one of the BCAA’s ³⁵²⁾. Recently, the safe upper limit of leucine was set at 550 mg/kg bodyweight/day in adult men; however, future studies are needed to determine the safe upper limit for both other populations and a mixture of all 3 BCAA’s ³⁵³⁾.

Numerous acute studies in animals and humans have shown that consumption of either essential amino acids, BCAA’s, or leucine either at rest or following exercise increases skeletal muscle protein synthesis, decreases muscle protein degradation, or both ³⁵⁴⁾, ³⁵⁵⁾; however, there are few long-term studies of BCAA supplementation in resistance-trained athletes. Stoppani et al. ³⁵⁶⁾ supplemented trained subjects with either 14 g BCAAs, whey protein, or a carbohydrate placebo for eight weeks during a periodized strength training routine. After training the BCAA group had a 4 kg increase in lean mass, 2% decrease in body fat percentage, and 6 kg increase in bench press 10 repetition maximum. All changes were significant compared to the other groups. However, it should be noted that this data is only available as an abstract and has yet to undergo the rigors of peer-review.

The use of BCAA’s between meals may also be beneficial to keep protein synthesis elevated. Recent data from animal models suggest that consumption of BCAA’s between meals can overcome the refractory response in protein synthesis that occurs when plasma amino acids are elevated, yet protein synthesis is reduced ³⁵⁷⁾. However, long-term human studies examining the effects of a diet in which BCAA’s are consumed between meals on lean mass and strength have not been done to date. It should also be noted that BCAA metabolism in humans and rodents differ and the results from rodent studies with BCAA’s may not translate in human models ³⁵⁸⁾. Therefore, long-term studies are needed in humans to determine the effectiveness of this practice.

Based on the current evidence, it is clear BCAA’s stimulate protein synthesis acutely and one study ³⁵⁹⁾ has indicated that BCAA’s may be able to increase lean mass and strength when added to a strength training routine; however, additional long-term studies are needed to determine the effects of BCAA’s on lean mass and strength in trained athletes. In addition, studies are needed on the effectiveness of BCAA supplementation in individuals following a vegetarian diet in which consumption of high-quality proteins are low as this may be population that may benefit from BCAA consumption. Furthermore, the effects of BCAA ingestion between meals needs to be further investigated in a long-term human study.

Arginine

“NO supplements” containing arginine are consumed by bodybuilders pre-workout in an attempt to increase blood flow to the muscle during exercise, increase protein synthesis, and improve exercise performance. However, there is little scientific evidence to back these claims. Fahs et al. ³⁶⁰⁾ supplemented healthy young men with 7 g arginine or a placebo prior to exercise and observed no significant change in blood flow following exercise. Additionally, Tang et al. ³⁶¹⁾ supplemented either 10 g arginine or a placebo prior to exercise and found no significant increase in blood flow or protein synthesis following exercise. Moreover, arginine is a non essential amino acid and prior work has established that essential amino acids alone stimulate protein synthesis ³⁶²⁾. Based on these findings, it appears that arginine does not significantly increase blood flow or enhance protein synthesis following exercise.

The effects of arginine supplementation on performance are controversial. Approximately one-half of acute and chronic studies on arginine and exercise performance have found significant benefits with arginine supplementation, while the other one-half has found no significant benefits ³⁶³⁾. Moreover, Greer et al. ³⁶⁴⁾ found that arginine supplementation significantly reduced muscular endurance by 2–4 repetitions on chin up and push up endurance tests. Based on these results, the authors of a recent review concluded that arginine supplementation had little impact on exercise performance in healthy individuals ³⁶⁵⁾. Although the effects of arginine on blood flow, protein synthesis, and exercise performance require further investigation, dosages commonly consumed by athletes are well below the observed safe level of 20 g/d and do not appear to be harmful ³⁶⁶⁾.

Citrulline malate

Citrulline malate (CitM) has recently become a popular supplement among bodybuilders; however, there has been little scientific research in healthy humans with this compound. CitM is hypothesized to improve performance through three mechanisms: 1) citrulline is important part of the urea cycle and may participate in ammonia clearance, 2) malate is a tricarboxylic acid cycle intermediate that may reduce lactic acid accumulation, and 3) citrulline can be converted to arginine; however, as discussed previously, arginine does not appear to have an ergogenic effect in young healthy athletes so it is unlikely CitM exerts an perfromance enhancing effect through this mechanism ³⁶⁷⁾.

Supplementation with CitM for 15 days has been shown to increase ATP production by 34% during exercise, increase the rate of phosphocreatine recovery after exercise by 20%, and reduce perceptions of fatigue [184]. Moreover, ingestion of 8 g CitM prior to a chest workout significantly increased repetitions performed by approximately 53% and decreased soreness by 40% at 24 and 48 hours post-workout ³⁶⁸⁾. Furthermore, Stoppani et al. ³⁶⁹⁾ in an abstract reported a 4 kg increase in lean mass, 2 kg decrease in body fat percentage, and a 6 kg increase in 10 repetition maximum bench press after consumption of a drink containing 14 g BCAA, glutamine, and CitM during workouts for eight weeks; although, it is not clear to what degree CitM contributed to the outcomes observed. However, not all studies have supported ergogenic effects of CitM. Sureda et al. ³⁷⁰⁾ found no significant difference in race time when either 6 g CitM or a placebo were consumed prior to a 137 km cycling stage. Hickner et al. ³⁷¹⁾ found that treadmill time to exhaustion was significantly impaired, with the time taken to reach exhaustion occurring on average seven seconds earlier following CitM consumption.

Additionally, the long-term safety of CitM is unknown. Therefore, based on the current literature a decision on the efficacy of CitM cannot be made. Future studies are needed to conclusively determine if CitM is ergogenic and to determine its long term safety.

Glutamine

Glutamine is the most abundant non-essential amino acid in muscle and is commonly consumed as a nutritional supplement. Glutamine supplementation in quantities below 14 g/d appear to be safe in healthy adults ³⁷²⁾; however, at present there is little scientific evidence to support the use of glutamine in healthy athletes ³⁷³⁾. Acutely, glutamine supplementation has not been shown to significantly improve exercise performance ³⁷⁴⁾, ³⁷⁵⁾, improve buffering capacity ³⁷⁶⁾, help to maintain immune function or reduce muscle soreness after exercise ³⁷⁷⁾. Long-term supplementation studies including glutamine in cocktails along with creatine monohydrate, whey protein, BCAA’s, and/or CitM have shown 1.5 – 2 kg increases in lean mass and 6 kg increase in 10RM bench press strength ³⁷⁸⁾, ³⁷⁹⁾. However, the role of glutamine in these changes is unclear. Only one study ³⁸⁰⁾ has investigated the effects of glutamine supplementation alone in conjunction with a six week strength training program. No significant differences in muscle size, strength, or muscle protein degradation were observed between groups. Although the previous studies do not support the use of glutamine in bodybuilders during contest preparation, it should be noted that glutamine may be beneficial for gastrointestinal health and peptide uptake in stressed populations ³⁸¹⁾; therefore, it may be beneficial in dieting bodybuilders who represent a stressed population. As a whole, the results of previous studies do not support use of glutamine as an ergogenic supplement; however, future studies are needed to determine the role of glutamine on gastrointestinal health and peptide transport in dieting bodybuilders.

Whey protein

Milk protein is mostly composed of whey protein 20% and casein 80% ³⁸²⁾. During cheese manufacturing, whey protein is generated as a by-product of casein precipitation. Whey protein is the most popular protein supplement sold in powder format. It contains valuable food ingredients because of its nutritional value and functional bioactivity. Whey protein contains β-lactoglobulin, α-lactalbumin, immunoglobulins, bovine serum albumin, lactoferrin, lactoperoxidase, phospholipoprotein, bioactive factors, and enzymes in order of abundance ³⁸³⁾. The biological components of whey protein and its isolates have been reported to benefit antioxidation ³⁸⁴⁾ and regulation of lipid metabolism ³⁸⁵⁾ and have antifatigue ³⁸⁶⁾ and antidiabetic properties ³⁸⁷⁾.

Whey protein isolates contain enriched essential amino acids, including branched chain amino acids, which the body needs for tissue synthesis, energy, and health. The high leucine content (50%–75% more than other protein sources), one of the branched chain amino acids, in whey protein could explain its ability to stimulate muscle protein synthesis ³⁸⁸⁾ and upregulate mammalian target of rapamycin signaling in high concentration. With whey protein supplementation, resistance exercises can result in muscle adaption and hypertrophy, regardless of the contraction mode (Whey protein hydrolysate augments tendon and muscle hypertrophy independent of resistance exercise contraction mode. Farup J, Rahbek SK, Vendelbo MH, Matzon A, Hindhede J, Bejder A, Ringgard S, Vissing K. Scand J Med Sci Sports. 2014 Oct; 24(5):788-98. https://www.ncbi.nlm.nih.gov/pubmed/23647357/()). Whey protein is marketed as a dietary supplement and as an aid for muscle development with resistance training. Because of its rapid rate of digestion, whey protein provides a rapid source of amino acids that can be taken up by the muscles to repair and rebuild muscular tissue. The use of whey protein to enhance aerobic exercises and swimming training has only been reported in terms of glycogen storage ³⁸⁹⁾, antioxidation ³⁹⁰⁾, and lipid metabolism. A combination of resistant exercise and WP benefitted the lipid profile, especially plasma triglycerides and cholesterol ³⁹¹⁾. Few reports have shown the beneficial synergistic effects of whey protein and long-term aerobic exercise training on biochemical profiles in specific tissues.

Resistance exercise, eccentric (muscle lengthening), isometric (non-lengthening) and concentric (shortening) contractions cause skeletal muscle damage and generate inflammatory markers (muscle proteins in blood) (The exercise-induced stress response of skeletal muscle, with specific emphasis on humans. Morton JP, Kayani AC, McArdle A, Drust B. Sports Med. 2009; 39(8):643-62. https://www.ncbi.nlm.nih.gov/pubmed/19769414/()). Anabolic interventions with protein hydrolysates and amino acid supplements have been evidenced to expedite the repair. Leucine-derived metabolite β-hydroxy-β-methylbutyrate ingestion has proved beneficial in recovery from the soreness. Resistance exercise (weight-lifting) elevates oxidation products in plasma, perturbs leukocyte redistribution and leukocyte functionality. Whey protein isolate nanoparticles were prepared using ethanol desolvation and their capacity to incorporate ZnCl2 was analysed. The amount of zinc incorporated in the particle suspensions was within the range of daily zinc requirements for healthy adults. Also, the nanoparticles remained stable after 30 days of storage at 22 °C. Cell surface glucose transporter 4 (GLUT 4) is the major glucose transporter isoform expressed in skeletal muscle that determines the rate of muscle glucose transport in the cell membrane, in response to insulin and muscle contraction. Whey protein hydrolysate was evaluated for its ability to translocate GLUT 4 and accumulate them in the membrane thereby augmenting glucose trapping by skeletal muscle. The amino acid l-isoleucine and the peptide l-leucyl-l-isoleucine in the hydrolysate contributed the most ³⁹²⁾. The effect of whey supplementation in comparison to casein diet, on the recovery of muscle functional properties such as contractility, extensibility, elasticity and excitability was investigated in rats. The whey protein diet promoted a faster recovery from injury sustained due to isometric as well as concentric exercise in comparison to the casein diet ³⁹³⁾. The effect of the supplementation of a beverage with varying doses of leucine or a mixture of branched chain amino acids on myofibrillar protein synthesis after resistance exercise was assessed. Results showed that low-protein (6.25 g) beverage can be as effective as a high-protein dose (25 g) at stimulating myofibrillar protein synthesis rates when supplemented with a high (5 g) leucine content. As leucine comprises 10 % of the total whey amino acid, the latter appears important for augmenting muscle hypertrophy. Health parameters, performance and body composition effects produced by 12 week intake of hydrolysed whey protein were compared in players. Intervention with the hydrolysed whey protein resulted in significant reduction in the muscle damage markers (creatine kinase and lactate dehydrogenase). Muscle mass growth by daily consumption of whey protein was compared with that of soy protein, using a randomized study on subjects undergoing resistance exercise ³⁹⁴⁾. Lean body mass gains were significantly high in whey protein than soy protein group and the remarkable response was correlated with the elevated levels of leucine and faster absorption.

Concerning lean body mass, many studies reported that protein synthesis could be upregulated by the branched chain amino acids of whey protein, especially leucine ³⁹⁵⁾. The combination of daily supplementation with whey protein and resistance exercise training was effective in promoting muscle hypertrophy ³⁹⁶⁾.

Whey protein consumption at intake levels up to 3 g/kg per day had a no-observed-adverse-effect level ³⁹⁷⁾ and the hydrolysate of whey protein at 2 g/kg as a food additive resulted in no adverse effects or mortality ³⁹⁸⁾. In this study, the whey protein dose was 4.1 g/kg, which is equivalent to 20 g of whey protein per 60 kg body weight for humans did not reveal any adverse effects ³⁹⁹⁾.

Based on their concentration and attributes, whey proteins are marketed in various forms such as whey protein concentrate (has fat and lactose along with proteins (29–89 %)), whey protein isolate (90 % protein) and whey protein hydrolysate (partially digested for ease of metabolism and hypo-allergenicity) ⁴⁰⁰⁾. A broad range of functionality has been assigned to whey protein and its derivatives, such as reduction of oxidative stress, promotion of muscle growth and lean body mass, appetite suppression, hypoglycemia, cardiovascular risk mitigation, phenylketonuria management and protection from ultraviolet (UV) radiation ⁴⁰¹⁾. Further, its role in food processing such as emulsifier, texturizer, fat-replacer, encapsulating agent, delivery vehicle and antimicrobial film are being recognized ⁴⁰²⁾.

What are Anabolic Steroids ?

Anabolic steroids are synthetic substances related to the male sex hormone testosterone. The proper term for these compounds is anabolic-androgenic steroids. “Anabolic” refers to muscle building, and “androgenic” refers to increased male sex characteristics. Some common names for anabolic steroids are Gear, Juice, Roids, and Stackers. They promote the growth of skeletal muscle (anabolic effects) and the development of male sexual characteristics (androgenic effects) in both males and females ⁴⁰³⁾. The term “anabolic steroids” will be used throughout this report because of its familiarity, although the proper term for these compounds is “anabolic-androgenic steroids.”

Anabolic steroids were developed in the late 1930s primarily to treat hypogonadism, a condition in which the testes do not produce sufficient testosterone for normal growth, development, and sexual functioning. The primary medical uses of these compounds are to treat delayed puberty, some types of impotence, and wasting of the body caused by HIV infection or other diseases.

During the 1930s, scientists discovered that anabolic steroids could facilitate the growth of skeletal muscle in laboratory animals, which led to abuse of the compounds first by bodybuilders and weightlifters and then by athletes in other sports. Steroid abuse has become so widespread in athletics that it can affect the outcome of sports contests.

Illicit steroids are often sold at gyms, competitions, and through mail order operations after being smuggled into this country. Most illegal steroids in the United States are smuggled from countries that do not require a prescription for the purchase of steroids. Steroids are also illegally diverted from U.S. pharmacies or synthesized in clandestine laboratories.

What are steroidal supplements ?

In the United States, supplements such as tetrahydrogestrinone (THG) and androstenedione (street name “Andro”) previously could be purchased legally without a prescription through many commercial sources, including health food stores ⁴⁰⁴⁾. Steroidal supplements can be converted into testosterone or a similar compound in the body. Less is known about the side effects of steroidal supplements, but if large quantities of these compounds substantially increase testosterone levels in the body, then they also are likely to produce the same side effects as anabolic steroids themselves. The purchase of these supplements, with the notable exception of dehydroepiandrosterone (DHEA), became illegal after the passage in 2004 of amendments to the Controlled Substances Act.

Commonly Abused Steroids

Oral Steroids

• Anadrol (oxymetholone)
• Oxandrin (oxandrolone)
• Dianabol (methandrostenolone)
• Winstrol (stanozolol)

Injectable Steroids

• Deca-Durabolin (nandrolone decanoate)
• Durabolin (nandrolone phenpropionate)
• Depo-Testosterone (testosterone cypionate)
• Equipoise (boldenone undecylenate)
• Tetrahydrogestrinone (THG).

How are anabolic steroids abused ?

Some anabolic steroids are taken orally, others are injected intramuscularly and still others are provided in gels or creams that are applied to the skin ⁴⁰⁵⁾. Doses taken by abusers can be 10 to 100 times higher than the doses used for medical conditions ⁴⁰⁶⁾.

Cycling, stacking, and pyramiding

Steroids are often abused in patterns called “cycling,” which involve taking multiple doses of steroids over a specific period of time, stopping for a period, and starting again ⁴⁰⁷⁾. Users also frequently combine several different types of steroids in a process known as “stacking.” Steroid abusers typically “stack” the drugs, meaning that they take two or more different anabolic steroids, mixing oral and/or injectable types, and sometimes even including compounds that are designed for veterinary use ⁴⁰⁸⁾. Abusers think that the different steroids interact to produce an effect on muscle size that is greater than the effects of each drug individually, a theory that has not been tested scientifically ⁴⁰⁹⁾.

Another mode of steroid abuse is referred to as “pyramiding.” This is a process in which users slowly escalate steroid abuse (increasing the number of steroids or the dose and frequency of one or more steroids used at one time), reaching a peak amount at mid-cycle and gradually tapering the dose toward the end of the cycle ⁴¹⁰⁾. Often, steroid abusers pyramid their doses in cycles of 6 to 12 weeks. At the beginning of a cycle, the person starts with low doses of the drugs being stacked and then slowly increases the doses. In the second half of the cycle, the doses are slowly decreased to zero. This is sometimes followed by a second cycle in which the person continues to train but without drugs. Abusers believe that pyramiding allows the body time to adjust to the high doses, and the drug-free cycle allows the body’s hormonal system time to recuperate. As with stacking, the perceived benefits of pyramiding and cycling have not been substantiated scientifically ⁴¹¹⁾.

Why do people abuse anabolic steroids ?

One of the main reasons people give for abusing steroids is to improve their athletic performance ⁴¹²⁾. Among athletes, steroid abuse has been estimated to be less that 6 percent according to surveys, but anecdotal information suggests more widespread abuse. Although testing procedures are now in place to deter steroid abuse among professional and Olympic athletes, new designer drugs constantly become available that can escape detection and put athletes willing to cheat one step ahead of testing efforts. This dynamic, however, may be about to shift if the saving of urine and blood samples for retesting at a future date becomes the standard. The high probability of eventual detection of the newer designer steroids, once the technology becomes available, plus the fear of retroactive sanctions, should give athletes pause.

Another reason people give for taking steroids is to increase their muscle size or to reduce their body fat ⁴¹³⁾. This group includes people suffering from the behavioral syndrome called muscle dysmorphia, which causes them to have a distorted image of their bodies. Men with muscle dysmorphia think that they look small and weak, even if they are large and muscular. Similarly, women with this condition think that they look fat and flabby, even though they are actually lean and muscular.

Some people who abuse steroids to boost muscle size have experienced physical or sexual abuse ⁴¹⁴⁾. In one series of interviews with male weightlifters, 25 percent who abused steroids reported memories of childhood physical or sexual abuse. Similarly, female weightlifters who had been raped were found to be twice as likely to report use of anabolic steroids or another purported musclebuilding drug, compared with those who had not been raped. Moreover, almost all of those who had been raped reported that they markedly increased their bodybuilding activities after the attack. They believed that being bigger and stronger would discourage further attacks because men would find them either intimidating or unattractive.

Finally, some adolescents abuse steroids as part of a pattern of high-risk behaviors ⁴¹⁵⁾. These adolescents also take risks such as drinking and driving, carrying a gun, driving a motorcycle without a helmet, and abusing other illicit drugs. Conditions such as muscle dysmorphia, a history of physical or sexual abuse, or a history of engaging in high-risk behaviors have all been associated with an increased risk of initiating or continuing steroid abuse.

Are anabolic steroids addictive ?

An undetermined percentage of steroid abusers may become addicted to the drugs, as evidenced by their continued abuse despite physical problems and negative effects on social relations. Also, steroid abusers typically spend large amounts of time and money obtaining the drugs, which is another indication that they may be addicted. Individuals who abuse steroids can experience withdrawal symptoms when they stop taking steroids, such as mood swings, fatigue, restlessness, loss of appetite, insomnia, reduced sex drive, and steroid cravings. The most dangerous of the withdrawal symptoms is depression, because it sometimes leads to suicide attempts. If left untreated, some depressive symptoms associated with anabolic steroid withdrawal have been known to persist for a year or more after the abuser stops taking the drugs.

People who abuse steroids may experience withdrawal symptoms when they stop use, including:

• mood swings
• fatigue
• restlessness
• loss of appetite
• sleep problems
• decreased sex drive
• steroid cravings.

One of the more serious withdrawal symptoms is depression, which can sometimes lead to suicide attempts.

What are the health consequences of steroid abuse ?

Anabolic steroid abuse has been associated with a wide range of adverse side effects ranging from some that are physically unattractive, such as acne and breast development in men, to others that are life threatening, such as heart attacks and liver cancer. Most are reversible if the abuser stops taking the drugs, but some are permanent, such as voice deepening in females.

Most data on the long-term effects of anabolic steroids in humans come from case reports rather than formal epidemiological studies. From the case reports, the incidence of lifethreatening effects appears to be low, but serious adverse effects may be underrecognized or underreported, especially since they may occur many years later. Data from animal studies seem to support this possibility. One study found that exposing male mice for one-fifth of their lifespan to steroid doses comparable to those taken by human athletes caused a high frequency of early deaths.

Anabolic steroids affect the brain

Anabolic steroids work differently from other drugs of abuse; they do not have the same short-term effects on the brain. The most important difference is that steroids do not trigger rapid increases in the brain chemical dopamine, which causes the “high” that drives people to abuse other substances. However, long-term steroid abuse can act on some of the same brain pathways and chemicals—including dopamine, serotonin, and opioid systems—that are affected by other drugs. This may result in a significant effect on mood and behavior.

Short-Term Effects

Abuse of anabolic steroids may lead to mental problems, such as:

• paranoid (extreme, unreasonable) jealousy
• extreme irritability
• delusions—false beliefs or ideas
• impaired judgment

Extreme mood swings can also occur, including “roid rage”—angry feelings and behavior that may lead to violence.

Aside from mental problems, steroid use commonly causes severe acne. It also causes the body to swell, especially in the hands and feet.

Long-Term Effects

Anabolic steroid abuse may lead to serious, even permanent, health problems such as:

• kidney problems or failure
• liver damage
• enlarged heart, high blood pressure, and changes in blood cholesterol, all of which increase the risk of stroke and heart attack, even in young people

Several other effects are gender- and age-specific:

In men:

• shrinking testicles
• decreased sperm count
• baldness
• development of breasts
• increased risk for prostate cancer.

In women:

• growth of facial hair or excess body hair
• male-pattern baldness
• changes in or stop in the menstrual cycle
• enlarged clitoris
• deepened voice.

In teens:

• stunted growth (when high hormone levels from steroids signal to the body to stop bone growth too early)
• stunted height (if teens use steroids before their growth spurt).

Some of these physical changes, such as shrinking sex organs in men, can add to mental side effects such as mood disorders.

Hormonal system

Steroid abuse disrupts the normal production of hormones in the body, causing both reversible and irreversible changes. Changes that can be reversed include reduced sperm production and shrinking of the testicles (testicular atrophy). Irreversible changes include male-pattern baldness and breast development (gynecomastia) in men. In one study of male bodybuilders, more than half had testicular atrophy and/or gynecomastia.

In the female body, anabolic steroids cause masculinization. Breast size and body fat decrease, the skin becomes coarse, the clitoris enlarges, and the voice deepens. Women may experience excessive growth of body hair but lose scalp hair. With continued administration of steroids, some of these effects become irreversible.

Musculoskeletal system

Rising levels of testosterone and other sex hormones normally trigger the growth spurt that occurs during puberty and adolescence and provide the signals to stop growth as well. When a child or adolescent takes anabolic steroids, the resulting artificially high sex hormone levels can prematurely signal the bones to stop growing.

Cardiovascular system

Steroid abuse has been associated with cardiovascular diseases (CVD), including heart attacks and strokes, even in athletes younger than 30. Steroids contribute to the development of CVD, partly by changing the levels of lipoproteins that carry cholesterol in the blood. Steroids, particularly oral steroids, increase the level of low-density lipoprotein (LDL) and decrease the level of high-density lipoprotein (HDL). High LDL and low HDL levels increase the risk of atherosclerosis, a condition in which fatty substances are deposited inside arteries and disrupt blood flow. If blood is prevented from reaching the heart, the result can be a heart attack. If blood is prevented from reaching the brain, the result can be a stroke.

Steroids also increase the risk that blood clots will form in blood vessels, potentially disrupting blood flow and damaging the heart muscle so that it does not pump blood effectively.

Liver

Steroid abuse has been associated with liver tumors and a rare condition called peliosis hepatis, in which blood-filled cysts form in the liver. Both the tumors and the cysts can rupture, causing internal bleeding.

Skin

Steroid abuse can cause acne, cysts, and oily hair and skin.

Infections

Many abusers who inject anabolic steroids may use nonsterile injection techniques or share contaminated needles with other abusers. In addition, some steroid preparations are manufactured illegally under nonsterile conditions. These factors put abusers at risk for acquiring lifethreatening viral infections, such as HIV and hepatitis B and C. Abusers also can develop endocarditis, a bacterial infection that causes a potentially fatal inflammation of the inner lining of the heart. Bacterial infections also can cause pain and abscess formation at injection sites.

What effects do anabolic steroids have on behavior ?

Case reports and small studies indicate that anabolic steroids, when used in high doses, increase irritability and aggression. Some steroid abusers report that they have committed aggressive acts, such as physical fighting or armed robbery, theft, vandalism, or burglary. Abusers who have committed aggressive acts or property crimes generally report that they engage in these behaviors more often when they take steroids than when they are drug free. A recent study suggests that the mood and behavioral effects seen during anabolic-androgenic steroid abuse may result from secondary hormonal changes.

Scientists have attempted to test the association between anabolic steroids and aggression by administering high steroid doses or placebo for days or weeks to human volunteers and then asking the people to report on their behavioral symptoms. To date, four such studies have been conducted. In three, high steroid doses did produce greater feelings of irritability and aggression than did placebo, although the effects appear to be highly variable across individuals. In one study, the drugs did not have that effect. One possible explanation, according to the researchers, is that some but not all anabolic steroids increase irritability and aggression. Recent animal studies show an increase in aggression after steroid administration.

In a few controlled studies, aggression or adverse, overt behaviors resulting from the administration of anabolic steroid use have been reported by a minority of volunteers.

In summary, the extent to which steroid abuse contributes to violence and behavioral disorders is unknown. As with the health complications of steroid abuse, the prevalence of extreme cases of violence and behavioral disorders seems to be low, but it may be underreported or underrecognized.

Research also indicates that some users might turn to other drugs to alleviate some of the negative effects of anabolic steroids. For example, a study of 227 men admitted in 1999 to a private treatment center for addiction to heroin or other opioids found that 9.3 percent had abused anabolic steroids before trying any other illicit drug. Of these 9.3 percent, 86 percent first used opioids to counteract insomnia and irritability resulting from anabolic steroids.

What treatments are effective for anabolic steroid abuse ?

Few studies of treatments for anabolic steroid abuse have been conducted. Current knowledge is based largely on the experiences of a small number of physicians who have worked with patients undergoing steroid withdrawal. The physicians have found that supportive therapy is sufficient in some cases. Patients are educated about what they may experience during withdrawal and are evaluated for suicidal thoughts. If symptoms are severe or prolonged, medications or hospitalization may be needed.

Some medications that have been used for treating steroid withdrawal restore the hormonal system after its disruption by steroid abuse. Other medications target specific withdrawal symptoms—for example, antidepressants to treat depression and analgesics for headaches and muscle and joint pains.

Some patients require assistance beyond pharmacological treatment of withdrawal symptoms and are treated with behavioral therapies.

Summary

Abuse of anabolic steroids differs from the abuse of other illicit substances because the initial abuse of anabolic steroids is not driven by the immediate euphoria that accompanies most drugs of abuse, such as cocaine, heroin, and marijuana, but by the desire of abusers to change their appearance and performance, characteristics of great importance to adolescents. The effects of steroids can boost confidence and strength, leading abusers to overlook the potential serious and long-term damage that these substances can cause.

While anabolic steroids can enhance certain types of performance or appearance, they are dangerous drugs, and when used inappropriately they can cause a host of severe, long-lasting, and in some cases, irreversible negative health consequences. Anabolic steroids can lead to early heart attacks, strokes, liver tumors, kidney failure, and serious psychiatric problems. In addition, because steroids are often injected, users who share needles or use nonsterile techniques when they inject steroids are at risk for contracting dangerous infections, such as HIV/AIDS and hepatitis B and C.

Possible Health Consequences of Anabolic Steroid Abuse

Hormonal system

Men

• infertility
• breast development
• shrinking of the testicles
• male-pattern baldness

Women

• enlargement of the clitoris
• excessive growth of body hair
• male-pattern baldness

Musculoskeletal system

• short stature (if taken by adolescents)
• tendon rupture

Cardiovascular system

• increases in LDL (bad) cholesterol;
• decreases in HDL (good) cholesterol;
• high blood pressure
• heart attacks
• enlargement of the heart’s left ventricle

Liver

• cancer
• peliosis hepatis (blood-filled cysts form in the liver)
• tumors
• Both the tumors and the cysts can rupture, causing internal bleeding.

Skin

• severe acne and cysts
• oily scalp
• jaundice
• fluid retention

Infection

• HIV/AIDS
• hepatitis B and C.

Psychiatric effects

• rage, aggression
• mania
• delusions