GENDER AND EXERCISE DURATION AFFECT EXERCISE-INDUCED GROWTH HORMONE RELEASE

The relationship between exercise intensity and growth hormone (GH) release in young men and women has recently been shown to be linear (1). However, the effect of exercise duration on serum GH concentration has not been investigated. To determine this effect, 8 young men [age=28±4 yr, ht=180±6 cm, wt=71.8±9.1 kg, percent body fat=11.3±2.9%, VO2peak=57.4±5.3 ml/kg/min (mean±SD)] and 7 young women [age=27±6 yr, ht=170±5 cm, wt=64.8±6.9 kg, percent body fat=18.3±5.5%, VO2peak=36.5±5.8 ml/kg/min] completed 3 randomly assigned exercise sessions on an electronically braked cycle ergometer (Lode) for durations of 30, 60 and 120 min at 70% VO2peak. In some sessions, work load was reduced so that the subject could continue for the entire allotted time. Thus, total work (TW) completed was calculated for each exercise session. Serum was collected at 10-min intervals for 4 hours, beginning 30 min prior to exercise. GH concentrations were measured via an enhanced sensitivity chemiluminescence assay (Nichols Diagnostic) and integrated GH concentration (IGHC) was calculated by trapezoidal reconstruction. All data were log transformed for statistical analysis. ANOVA with repeated measures revealed a significant main effect for exercise duration (p<0.001) and a trend for a significant gender by duration interaction (p=0.059). Subsequent regression analysis of log(IGHC) versus log(exercise time), revealed that the slope was greater in men than women (0.928 vs 0.476, respectively) (p=0.008). The present data indicate that at the same relative exercise intensity, young men and women have similar GH responses at exercise durations of 30 and 60 min. However, the 120-min exercise duration resulted in greater attenuation of the GH response in young women compared to young men.

References: Pritzlaff-Roy et al., JAP 92: 2053-2060, 2002