GH secretion in acute exercise may result in post-exercise lipolysis

Exercise is a potent stimulator of growth hormone (GH) secretion. We hypothesised that after a short bout of intense exercise GH may increase lipolysis during recovery. In 7 moderately trained young male subjects (21.8 ± 0.5 years) and 7 moderately trained older male subjects (56.0 ± 1.0 years) [2H5] glycerol was infused for 370 min to measure glycerol production rate (Ra), a measure of lipolysis. At 130 min subjects exercised on a cycle ergonometer for 20 min at 70% VO2max, followed by rest for 220 min. On a separate occasion the study was repeated in the young subjects with a 1 h GH infusion (4μg kg−1 h−1) at 130 min instead of exercise. In response to exercise, catecholamines (p < 0.02) and glycerol Ra (p < 0.01) increased, peaking during exercise. GH concentration increased in response to exercise (p < 0.01), peaking after exercise (150-160 min) in both groups with no significant difference in peak response between groups. A post-exercise rise in glycerol Ra was demonstrated in both groups peaking at 265-295 min in the older group (p < 0.002, peak vs. basal) and continuing to rise until 370 min in the young group (p < 0.01, peak vs. basal). The timing and magnitude of this was reproduced with the GH infusion. There was a significant correlation between the peak GH response to exercise and the post-exercise rise in glycerol Ra measured as area under the curve (r = 0.57, p < 0.04). In conclusion, this study provides evidence that the GH response to acute exercise may increase lipolysis during recovery.