We investigated the responses of serum testosterone (T) and human growth hormone (hGH) concentrations to a bout of heavy resistive exercise and the responses of T, hGH, and insulinlike growth factor I (IGF-I) to a 16 wk progressive resistive training program in 13 men (60 ± 4 yrs). Body composition via hydrostatic weighing and muscle strength using a 3 repetition maximum (3RM) test on 6 variable resistance exercise machines were assessed before and after the training program. Fasting blood samples were drawn on 2 consecutive days prior to training and again on 2 consecutive days after the last day of exercise. Blood was also drawn immediately before and ~ 10 min after a single exercise session during the first wk of training, and after an exercise session of the same relative resistance during the last wk of training. The training program resulted in a 37 % increase in upper body strength and a 39 % increase in lower body strength (both p < 0.01). Lean body mass increased significantly (61.8 ± 2.1 vs 63.7 ± 7.8 kg; p < 0.001) while % fat decreased (26.5 ± 1.5 vs 24.9 ± 6.0 %; p < 0.01) as a result of training. Serum T concentration was unchanged, but GH increased ~ 18-fold in response to a single bout of resistive exercise before (0.24 ± 0.08 vs 4.60 ± 1.35 mg/l) and after (0.26 ± 0.06 vs 4.66 ± 1.46 mg/l; p < 0.01) training. Baseline serum concentrations of T, hGH, and IGF-I were unaffected by the training program. We conclude that an acute bout of resistive exercise causes a substantial hGH response in older men, but 16 wks of progressive resistive training does not affect baseline concentrations of the anabolic hormones.
Key words
Strength training - human growth hormone - testosterone - insulin-like growth factor I
