ENDURANCE TRAINING AMPLIFIES THE PULSATILE RELEASE OF GROWTH-HORMONE - EFFECTS OF TRAINING INTENSITY

The effects of intensity of run training on the pulsatile release of growth hormone (GH) were investigated in 21 eumenorrheic untrained women. The O2 consumption (VO2) at the lactate threshold (LT); fixed blood lactate concentrations (FBLC) of 2.0, 2.5, and 4.0 mM; peak VO2; maximal VO2; body composition; and pulsatile release of GH were measured. Subjects in both the at-lactate threshold (@LT, n = 9) and above-lactate threshold (> LT, n = 7) training groups increased VO2 at LT and FBLC of 2.0, 2.5, and 4.0 mM and VO2max after 1 yr of run training. However, the increase observed in the >LT group was greater than that in the @LT group (P < 0.05). No change was observed for the control group (n = 5). No among- or within-group differences were observed for body weight, although trends for reductions in percent body fat (P < 0.06) and fat weight (P < 0.15) were observed in the >LT group, and both training groups significantly increased fat-free weight (P < 0.05). Significant differences (P < 0.05) in the pulsatile release of GH were observed within the >LT group, as a result of 1 yr of run training, for maximal peak height (7.4-mu-g/l pre vs. 13.1-mu-g/l post), incremental peak amplitude (6.8-mu-g/l pre vs. 10.3-mu-g/l post), peak area (340-mu-g.l-1.min-1 pre vs. 598-mu-g.l-1.min-1 post), nadir GH concentration (0.60-mu-g/l pre vs. 2.2-mu-g/l post), and integrated (24-h) concentration of GH (4,390-mu-g.l-1.min-1 pre vs. 7,710-mu-g.l-1.min-1 post). No changes were observed for these variables within the @LT or control group. Results of the present study indicate that exercise training amplifies the pulsatile release of GH. This effect occurs when some training is above the LT. Our findings may have clinical implications in conditions characterized by impoverished pulsatile secretion of GH.