Effects of one bout of maximum aerobic physical activity in morning and evening on plasma GH and cortisol levels in young female

Moderate and high-intensity exercise is a potent stimulus for growth hormone (GH) and cortisol secretion. Other factors such as circadian rhythms can also modulate the GH and cortisol responses to exercise. The purpose of this study was to determine the effects of daily exercise time on GH and cortisol response to exercise. 22 female university students (the mean age: 21.59±2.24 years, BMI: 21.05±2.75 kg/m2, body fat percent: 27.28±3.20 %) were randomly divided into experimental group (n=12) and control group (n=10). Subjects performed Bruce Protocol Stress Test on treadmill after 12 hours of fasting on two separate days. The first test was performed at 7:00 AM and the second one was conducted at 6:00 PM. Blood samples (10cc) were collected at both stages, immediately before and after exercise. The results of inter-group ANOVA and post-hoc test of Tukey showed a significant increase in the mean of serum GH after exercise in the morning and evening (p=0.001). The mean of serum cortisol had noticeably risen after exercise in the morning (p<0.05). A significant increase was also observed in GH/cortisole ratio after exercise in the evening (p<0.001).Discussion and With respect to the increase in plasma GH/cortisole ratio in the evening, it seems there exist better anabolism conditions in the body in the evening exercise.