Testosterone Dose-Dependently Increases Maximal Voluntary ...
Testosterone Dose-Dependently Increases Maximal Voluntary Strength and Leg Power, but Does Not Affect Fatigability or Specific Tension
Division of Endocrinology, Metabolism, and Molecular Medicine, Charles R. Drew University of Medicine and Science, Los Angeles, California 90059
Address all correspondence and requests for reprints to: Thomas W. Storer, Ph.D., Division of Endocrinology, Metabolism, and Molecular Medicine, Charles R. Drew University of Medicine and Science, 1731 East 120th Street, Los Angeles, California 90059. E-mail: tostorer@cdrewu.edu.
Testosterone supplementation in men increases fat-free mass, but whether measures of muscle performance, such as maximal voluntary strength, power, fatigability, or specific tension, are improved has not been determined. Furthermore, the extent to which these measures of muscle performance are related to testosterone dose or circulating concentration is unknown. To examine the relationship between testosterone dose and muscle performance, 61 healthy, eugonadal young men (aged 18&endash;35 yr) were randomized to 1 of 5 groups, each receiving a long-acting GnRH agonist to suppress endogenous testosterone production plus weekly injections of 25, 50, 125, 300, or 600 mg testosterone enanthate for 20 wk. These doses produced mean nadir testosterone concentrations of 253, 306, 542, 1345, and 2370 ng/dl, respectively. Maximal voluntary muscle strength and fatigability were determined by a seated leg press exercise. Leg power was measured using a validated leg power instrument. Specific tension was estimated by the ratio of one repetition maximum muscle strength to thigh muscle volume determined by magnetic resonance imaging. 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 = 0.0005) and free (r = 0.38; P = 0.006) testosterone as was leg power (total testosterone: r = 0.38; P = 0.007; free testosterone: r = 0.35; P = 0.015), but not muscle fatigability. Serum IGF-I concentrations were not significantly correlated with leg strength, power, or fatigability. Specific tension did not change significantly at any dose. We conclude that the effects of testosterone on muscle performance are specific; it increases maximal voluntary strength and leg power, but does not affect fatigability or specific tension. The changes in leg strength and power are dependent on testosterone dose and circulating testosterone concentrations and exhibit a log-linear relationship with serum total and free testosterone. Failure to observe a significant testosterone dose relationship with fatigability suggests that testosterone does not affect this component of muscle performance and that different components of muscle performance are regulated by different mechanisms.
This work was supported by NIH Grants 1RO1-AG-14369 and 1RO1-DK-59627-01, FDA Grant ODP 1397, General Clinical Research Center Grant MO1-RR-00425, and RCMI Grants P20-RR-11145-01 (RCMI Clinical Research Initiative) and G12RR03026.
R.C. is the Grancell-Burns Chair in the Rehabilitative Sciences at the Harbor-University of California-Los Angeles Research and Education Institute.
Abbreviations: ANCOVA, Analysis of covariance; BMI, body mass index; GCRC, General Clinical Research Center; MRI, magnetic resonance imaging; 1-RM, one repetition maximum.
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