The effect of exercise duration and mode on the growth hormone responses in young women on oral contraceptives.

Previous research is conflicting concerning the minimum time duration needed to elicit a growth hormone (GH) response to aerobic exercise; thus, the purpose of this project was to examine the effects of mode and duration on exercise-induced GH responses in young women taking oral contraceptives. Nine healthy young females on oral contraceptives exercised at 75% of their mode-specific peak aerobic power ( VO(2)peak) on the treadmill and cycle ergometer for 10, 15 and 20 min, with serial blood samples taken at rest and every 10 min throughout the entire 5.5 h of the study. Each exercise bout was followed by 70 min of rest. A significant ( P<0.02) GH response was observed at the end of exercise regardless of the duration or mode of exercise. The peak GH concentrations were 12.2 (1.8), 10.2 (1.6), and 7.6 (1.5) ng.ml(-1) for the 10-, 15-, and 20-min exercise bouts on the treadmill, respectively. For the cycle ergometer, peak GH concentrations were 9.3 (2.0), 6.3 (1.0), and 9.8 (1.7) ng.ml(-1), respectively. The total integrated area under the curve was not significantly different between the cycle and treadmill exercise for each exercise duration. Moderate-intensity aerobic exercise is sufficient to produce a GH response in as little as 10 min during both treadmill and cycling exercise in young women taking oral contraceptives. Overall, the mode of exercise does not impact the exercise-induced GH response.