Effects of lower- and higher- volume resistance exercise on serum testosterone and skeletal muscle androgen receptor content in men : subsequent effects on the mRNA expression of insulin- like growth factor peptide and myostatin in skeletal muscle.
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Spillane, Micheil Brian (Mike).
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Testosterone is the primary sex steroid hormone within males. Testosterone effects are ubiquitous and are categorized as either anabolic or androgenic. The androgen receptor is a specific nuclear hormone receptor through which testosterone elicits its effects. Specifically, skeletal muscle has androgen receptors present and is responsive to testosterone. The resulting activation of testosterone–androgen receptor–DNA binding increases muscle protein synthesis and reduces muscle protein breakdown. In addition, the testosterone level can alter the expression of insulin–like growth factor and myostatin which are key regulators of muscle protein balance. Higher-intensity resistance exercise in non-resistance-trained participants is known to increase endogenous serum testosterone levels. However, using resistance-trained participants the purpose of this study was to examine whether elevations in serum testosterone occur in response to a higher-intensity of resistance-exercise, and if this increase induces elevations in skeletal muscle testosterone, 5α-dihydrotestosterone (DHT), androgen receptor mRNA and protein content as well as possible interactions between muscle IGF-1 and myostatin mRNA expression. In a randomized cross-over design, venous blood was obtained in male participants immediately before and after, 30 minutes, 1 hour, 2 hours, 3 hours, and 24 hours after a single bout of resistance exercise. Muscle samples were obtained immediately before and after, 3 hours, 24 hours after exercise. Exercise bouts consisted of an upper-lower body (higher-volume) and lower-body (lower-volume) protocol. Each exercise bout was separated by one week of rest. Statistical analyses were performed by separate 2 x 7 and 2 x 4 (Session x Test) factorial analyses of variance (ANOVA) with repeated measures. The exercise protocol employed has previously been demonstrated to significantly increase serum testosterone. However, this study did not produce such a response. Neither exercise protocol significantly increased serum total or free testosterone (p > 0.05). Also, no changes were observed for muscle testosterone, DHT, androgen receptor mRNA expression or protein content (p > 0.05). In addition, no alterations in muscle IGF-1 or myostain were observed (p > 0.05). It was concluded that higher-intensity resistance exercise of the upper-body performed immediately prior to lower-body resistance exercise does not result in a significant elevation in testosterone in resistance-trained participants.