McCall, G. E., Byrnes, W. C., Fleck, S. J., Dickinson, A., & Kraemer, W. J. (1999). Acute and chronic hormonal responses to resistance training designed to promote muscle hypertrophy. Canadian Journal of Applied Physiology, 24, 96-107.

Weight-trained college men (N = 11) trained three times per week for 12 weeks (an average of 32 sessions). High-volume free weights and exercise-machine resistances were employed.

Forearm flexor 1-RM strength improved by 25%. Hypertrophy in both classes of muscle fibers and overall muscle circumference was observed.

Resting hormone concentrations and the patterns of acute exercise hormonal elevations during the fourth and eighth weeks were not changed by 12 weeks of training. Decreased plasma volume accounted for elevations in testosterone, insulin-like growth factor-I, and sex hormone-binding globulin during exercise. Growth hormone and cortisol remained significantly high when corrected for plasma volume losses. Only the acute exercise-induced growth hormone elevations were correlated with the magnitude of fiber hypertrophy following training.

Implication. Growth hormone stimulated during resistance training influences muscle hypertrophy.

Return to Table of Contents for this issue.