CHANGES IN INSULIN SENSITIVITY, GLUCOSE EFFECTIVENESS, AND B-CELL FUNCTION IN REGULARLY EXERCISING SUBJECTS

To determine the relative contributions of changes in glucose effectiv eness, B-cell function, and insulin sensitivity to changes in glucose tolerance upon exercise cessation in regularly exercising individuals, we studied seven young subjects who were performing aerobic exercise on a regular schedule. Each subject was studied 12 and 84 hours after the last bout of exercise with an intravenous glucose tolerance test ( IVGTT) to quantify insulin sensitivity and glucose effectiveness at ze ro insulin (GEZI) using the minimal model of glucose kinetics. Additio nally, B-cell function was quantified as the acute insulin response to glucose (AIRglucose), and intravenous glucose tolerance as the glucos e disappearance constant (K-g). Twelve hours after the last bout of ex ercise, S-I was 8.47 +/- 1.12 x 10(-5) min(-1)/pmol/L, as compared wit h 6.98 +/- 1.17 x 10(-5) min(-1)/pmol/L 84 hours after exercise (mean +/- SE, P=.005). No change was observed in GEZI (0.020 +/- 0.004 min(- 1) at 12 hours v 0.019 +/- 0.002 min(-1) at 84 hours, P = NS) or AIRgl ucose (588 +/- 213 pmol/L at 12 hours v 687 +/- 271 pmol/L at 84 hours , P = NS). Thus, the difference in intravenous glucose tolerance obser ved 12 hours after exercise as compared with 84 hours after the last b out of exercise (K-g, 2.91 +/- 0.70%/min at 12 hours v 2.23 +/- 0.60%/ min at 84 hours, P<.05) would appear to be entirely related to a diffe rence in S-I and not to differences in glucose effectiveness or B-cell function. Copyright (C) 1995 by W.B. Saunders Company