D’Antona, G., Lanfranconi, F., Pellegrino, M. A., Brocca, L., Adami, R., Rossi, R., Moro, G., Miotti, D., Canepari, M., Bottinelli, R. (2006). Skeletal muscle hypertrophy and structure and function of skeletal muscle fibers in male body builders. Journal of Physiology, 570(Pt 3), 611-627.

Needle biopsy samples were taken from the vastus lateralis muscles of male body builders (N = 5), who had being performing hypertrophic heavy resistance exercise (HHRE) for at least two years, and from active untrained male control Ss (N = 5).

In the body builders, a preferential hypertrophy of fast and especially Type 2X fibers was observed. The very large hypertrophy of the vastus lateralis muscles could not be fully accounted for by single muscle fiber hypertrophy. The cross-sectional area of vastus lateralis was 54% larger in body builders than in the controls. In comparison, the mean fiber area was only 14% larger. Myosin heavy chain isoform distribution was shifted towards 2X fibers in the body builders. Specific force was significantly lower in Type 1 fibers of the body builders than in Type 1 fibers from the controls. Type 2A and Type 2X fibers were significantly stronger in body builders than in the controls. The maximum shortening velocity of Type 1 fibers and actin sliding velocity of myosin 1 were significantly lower in the body builders than in the controls. There were no differences among fast fibers and myosin 2A.

The skeletal muscle of body builders was markedly adapted to hypertrophic heavy resistance exercise through extreme hypertrophy, a shift towards the stronger and more powerful fiber types and an increase in specific force of muscle fibers. [This shows the specific training effect and not some natural enhancement from drug taking. One has to question, why take anabolic steroids for performance improvement. They only embellish muscle size with that size not transferring to muscle strength. Steroids appear to enhance appearance only.] Such adaptations could not be fully accounted for by well known mechanisms of muscle plasticity, i.e. by the hypertrophy of single muscle fiber (quantitative mechanism) and by a regulation of contractile properties of muscle fibers based on MHC isoform content (qualitative mechanism). Two body builders took anabolic steroids and three did not. The former Ss differed from the latter Ss mostly in the size of their muscles and muscle fibers.

Implication. Hypertrophic heavy resistance exercise, the form of training usually undertaken by body builders, produces training adaptation in single muscle fiber hypertrophy and other unspecified factors. An hypothesis was formed that suggested anabolic steroid use only affected the size of muscles and their fibers. In essence, this study showed that training produces specific effects that are more substantial than steroid ingestion effects.

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