Effects of treadmill exercise to exhaustion on the insulin response to hyperglycemia in untrained men

The effects of a single bout of exercise to exhaustion on pancreatic insulin secretion were determined in seven untrained men by use of a 3-h hyperglycemic clamp with plasma glucose maintained at 180 mg/100 ml. Clamps were performed either 12 h after an intermittent treadmill run at ~77% maximum O₂ consumption or without prior exercise. Arterialized blood samples for glucose, insulin, and C-peptide determination were obtained from a heated hand vein. The peak insulin response during the early phase (0-10 min) of the postexercise clamp was higher (81 ± 8 vs. 59 ± 9 μU/ml; P< 0.05) than in the nonexercise clamp. Incremental areas under the insulin (376 ± 33 vs. 245 ± 51 μU·ml^-1·min) and C-peptide (17 ± 2 vs. 12± 1 ng·ml^-1·min) curves were also greater (P < 0.05) during the early phase of the postexercise clamp. No differences were observed in either insulin concentrations or whole body glucose disposal during the late phase (15-180 min). Area under the C-peptide curve was greater during the late phase of the postexercise clamp (650 ± 53 vs. 536 ± 76 ng·ml^-1·min, P < 0.05). The exercise bout induced muscle soreness and caused an elevation in plasma creatine kinase activity (142 ± 32 vs. 305 ± 31 IU/l; P < 0.05) before the postexercise clamp. We conclude that in untrained men a bout of running to exhaustion increased pancreatic β-cell insulin secretion during the early phase of the hyperglycemic clamp. Increased insulin secretion during the late phase of the clamp appeared to be compensated by increased insulin clearance.