RESPONSES OF IGF-I TO ENDOGENOUS INCREASES IN GROWTH-HORMONE AFTER HEAVY-RESISTANCE EXERCISE

The purpose of this study was to examine the effects of a heavy-resist ance exercise protocol known to dramatically elevate immunoreactive gr owth hormone (GH) on circulating insulin-like growth factor I (IGF-I) after the exercise stimulus. Seven men (23.1 +/- 2.4 yr) volunteered t o participate in this study. Each subject was asked to perform an eigh t-station heavy-resistance exercise protocol consisting of 3 sets of 1 0 repetition maximum resistances with 1-min rest between sets and exer cises followed by a recovery day. In addition, a control day followed a nonexercise day to provide baseline data. Pre- and postexercise (0, 15, and 30 min) blood samples were obtained and analyzed for lactate, creatine kinase, GH, and IGF-I. Postexercise values for lactate and GH were significantly(P < 0.05) elevated above preexercise and resting b aseline values. The highest mean GH concentration after the heavy-resi stance exercise protocol was 23.8 +/- 11.8 mu g/l, observed at the imm ediate postexercise time point. Significant increases in creatine kina se were observed after the exercise protocol and during the recovery d ay. No significant relationships were observed between creatine kinase and IGF-I concentrations. No significant changes in serum IGF-I conce ntrations were observed with acute exercise or between the recovery an d control days. Thus, these data demonstrate that a high-intensity bou t of heavy-resistance exercise that increases circulating GH did not a ppear to affect IGF-I concentrations over a 24-h recovery period in re creationally strength-trained and healthy young men.