INFLUENCE OF EXERCISE DURATION ON SERUM INSULIN-LIKE-GROWTH-FACTOR AND ITS BINDING-PROTEINS IN ATHLETES

The changes in circulating concentrations of insulin-like growth facto rs during exercise have to date remained incomplete in their documenta tion. Therefore, we examined in 25 healthy athletes the effects of thr ee different durations of three types of exercise - incremental ergome ter cycling exercise (ICE), long-distance Nordic ski race (NSR) and a treadmill-simulated soccer game (TSG) lasting 20 min, 3 h, and 2 x 45 min separated by a 15-min half-time rest respectively, on plasma conce ntrations of growth hormone ([GH]), insulin-like growth factor-1 I([IG F-I]) and its binding proteins 1 and 3 ([IGFBP-1], [IGFBP-3]). Compare d to baseline, serum [GH] increased by 15.2-fold after ICE(P < 0.001), 2.9-fold after NSR (P < 0.01) and 4.6-fold after TSG. Serum [IGF-I] r est by 11.9% after ICE(P < 0.001), while it decreased by -14.6% after NSR(P < 0.001) and was unchanged after TSG. Serum [IGFBP-1] was slight ly increased (1.7-fold) after ICE (P < 0.01), but increased markedly ( 11.8-fold) after NSR(P < 0.001) and by 6.3-fold after the second sessi on of TSG (P < 0.01) tit remained unchanged at the end of the first pe riod of TSG, i.e. after 45-min exercise). The [IGFBP-3] increased by 1 4.7% after ICE (P < 0.001) and by 6% after TSG (P < 0.05) while it did not change after NSR. From our results it would appear that [IGFBP-1] increase to bind free IGF and hinder their insulin-like action during long-term exercise (lasting beyond 45 min). It is suggested that IGFB P-1 might thus contribute both to preventing hypoglycaemic action of I GF and to facilitating glucose uptake by muscle cells when muscle glyc ogen stores become deplete.