Growth hormone responses to repeated bouts of aerobic exercise with different recovery intervals in cyclists

To characterise the specific GH responses to repeated bouts of standardised aerobic exercise in amateur competitive cyclists, 6 volunteers (mean age +/- SE: 28.7 +/- 2.3 yr, range: 18-35 yr) performed two consecutive 30-min cycling sessions at 80% of individual maximal oxygen uptake on three occasions with different time interval between bouts: 2 h (EXP A), 4 h (EXP B) and 6 h (EXP C). Serum GH concentration was determined in blood samples collected at 15-min intervals during exercise and following 1 h of recovery. In EXP A and EXP B, peak GH concentration in response to the second bout was significantly lower (p < 0.01) than that of the first bout, but in EXP C no difference was detected between bouts. Similarly, the average integrated GH concentration (AUC), determined during the exercise period and in the following 1 h of recovery in the course of the second bout, was significantly lower than that observed during the first bout only in EXP A (p < 0.05) and EXP B (p < 0.01) and not in EXP C, so that the second bout AUC of EXP C was significantly higher than that of EXP A (p < 0.01) and EXP B (p < 0.01). It was concluded that GH responses to subsequent bouts of aerobic exercise are dependent on the time interval between the exercise sessions.