Bosco, C., Colli, R., Bonomi, R., Von Duvillard, S. P., & Viru, A. (2000). Monitoring strength training: Neuromuscular and hormonal profile. Medicine and Science in Sports and Exercise, 32, 202-208.

This study investigated changes induced by a single heavy resistance training session on neuromuscular and endocrine systems in trained athletes, using the same exercises for training and testing. Ss included track sprinters (M = 6; F = 6), body builders (N = 6), weight lifters performing low-repetition exercises (N = 4) and high-repetition exercise (N = 4). Work performed in half- and full-squat exercises was monitored for mechanical power output and EMG activity. Blood samples were taken just before and after the exercises to monitor testosterone, human growth hormone, and other hormones.

Male sprinters demonstrated a significant decrease (-55% -- fatigue) in power in the full squat, cortisol, serum testosterone, and lutropin. This did not occur in the equivalent female group. Serum testosterone increased in the high-repetition weight lifters but not in the low-repetition lifters. Body builders exhibited a decrease in serum testosterone and human growth hormone. Women reacted differently, exhibiting less fatigue in the exercises and markedly different hormonal responses.

A different response was noted for half-squat (short, quick actions employing primarily fast-twitch fibers) and full-squat (longer, more slow-twitch fibers in use) exercises. In rapid actions, testosterone decreased and the maintenance of power was partially offset by an increase in muscle activation for a short while. On the other hand, when training volumes were higher, serum testosterone levels rose.

Implication. Low-repetition, fast-twitch fiber dominated exercises reduced serum testosterone and power output due to fatigue. High-repetition, slow-twitch fiber dominated exercises increased serum testosterone levels. These characteristics occurred only in males, the female response being much less and significantly different.

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