Testosterone effects on muscle performance

The data presented above have established that testosterone supplementation in men increases fat free mass, but it remains unclear whether measures of muscle performance such as maximal voluntary strength, power, fatigability, or specific tension are improved by androgen administration (Storer etal. 2003). Further, the extent to which these measures of muscle performance are related to testosterone dose or circulating concentration is unknown. To determine the dose-dependence of measures of muscle performance on testosterone dose and concentrations, we measured maximal voluntary strength, leg power, and muscle fatigability in our dose response study. Specific tension was estimated by the ratio of 1RM muscle strength to thigh muscle volume determined by MRI. Testosterone administration was associated with a dose-dependent increase in leg press strength and leg power, but muscle fatigability did not change significantly during treatment. Changes in leg press strength were significantly correlated with total (r = 0.46, P = 0.005) and free testosterone (r = 0.38, P = 0.006) as was leg power (r = 0.38, P = 0.007 for total and r = 0.35, P = 0.015 for free testosterone), but not muscle fatigability. Serum IGF-1 concentrations were not significantly correlated with leg strength, power, or fatigability. Specific tension did not change significantly at any dose.

These data led us to conclude that testosterone effects on muscle performance are domain-specific: it increases maximal voluntary strength and leg power, but does not affect fatigability or specific tension. Failure to observe a significant testosterone-dose relationship with fatigability suggests that testosterone does not affect this domain of muscle performance and that different domains of muscle performance are regulated by different mechanisms. We also infer from these data that the gains in maximal voluntary strength during testosterone administration are proportional to the increase in muscle mass, and that testosterone does not improve the contractile properties of the skeletal muscle.

Fig. 8.2 Testosterone induces skeletal muscle fiber hypertrophy

The figure shows cross-sections of muscle biopsies obtained before and after 20 weeks of treatment in one man treated with GnRH agonist and 600 mg testosterone enanthate weekly. The left panels represent baseline sections, and the right panels sections obtained after 20 weeks of treatment. The magnification is 200-fold in panels A and B, and 1000-fold in panels C and D. (Reproduced with permission from Sinha-Hikim etal. 2002.)

Fig. 8.2 Testosterone induces skeletal muscle fiber hypertrophy

The figure shows cross-sections of muscle biopsies obtained before and after 20 weeks of treatment in one man treated with GnRH agonist and 600 mg testosterone enanthate weekly. The left panels represent baseline sections, and the right panels sections obtained after 20 weeks of treatment. The magnification is 200-fold in panels A and B, and 1000-fold in panels C and D. (Reproduced with permission from Sinha-Hikim etal. 2002.)

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