Details

Autor(en) / Beteiligte

• Spillane, Mike

Titel

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

Ort / Verlag

ProQuest Dissertations & Theses

Erscheinungsjahr

2013

Quelle

ProQuest Dissertations & Theses A&I

Beschreibungen/Notizen

• 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, 5á-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.