INFLUENCE OF MODERATE PHYSICAL EXERCISE ON INSULIN-MEDIATED AND NON-INSULIN-MEDIATED GLUCOSE-UPTAKE IN HEALTHY-SUBJECTS

To establish the relative importance of insulin sensitivity and glucos e effectiveness during exercise using Bergman's minimal model, 12 nont rained healthy subjects were studied at rest and during 95 minutes of moderate exercise (50% maximum oxygen consumption [V over dotO(2)max]) . Each subject underwent two frequently sampled intravenous glucose to lerance tests (FSIGTs) for 90 minutes, at rest (FSIGTr) and during exe rcise (FSIGTe). Plasma glucose, insulin, and C-peptide were determined . Insulin sensitivity (S-1), glucose effectiveness at basal insulin (S -G), insulin action [X(t)], and first-phase (Phi(1)) and second-phase (Phi(2)) beta-cell responsiveness to glucose were estimated using both minimal models of glucose disposal (MMg) and insulin kinetics (MMI). Glucose effectiveness at zero insulin (GEZI), glucose tolerance index (K-G), and the area under the insulin curve (AUC(0.90)) were also calc ulated. Intravenous glucose tolerance improved significantly during ph ysical exercise. During exercise, S-I (FSIGTr v FSIGTe: 8.5 +/- 1.0 v 25.5 +/- 7.2 x 10(-5). min(-1) [pmol . L(-1)](-1), P < .01), S-G (0.19 5 +/- 0.03 v 0.283 +/- 0.03 x 10(-1). min(-1), P < .05), and GEZI (0.1 90 +/- 0.03 v 0.269 +/- 0.04 x 10(-1). min(-1), P < .05) increased; ho wever, no changes in Phi(1) and Phi(2) were found. Despite a significa nt decrease in the insulin response to glucose (AUC(0.90), 21,000 +/- 2,008 v 14,340 +/- 2,596 pmol . L(-1). min, P < .01), insulin action [ X(t)] was significantly higher during the FSIGTe. These results show t hat physical exercise improves mainly insulin sensitivity, and to a le sser degree, glucose effectiveness. During exercise, the insulin respo nse to glucose was lower than at rest, but beta-cell responsiveness to glucose did not change. Copyright (C) 1997 by W.B. Saunders Company.