Long-lasting effect of training on insulin responsiveness in the rat

In vivo insulin sensitivity and responsiveness were assessed in rats one day (Day 1), seven days (Day 7), and 3 weeks (Day 21) after cessation of training, using a 2-stage sequential hyperinsulinemic euglycemic clamp technique (insulin infusion rate: 4.4 mU.kg^-1 min^-1 and 26.4 mU.kg^-1.min^-1). The day after the last bout of exercise, the glucose infusion rate (GIR-L: 4.4 mU-dose), which is an index of insulin sensitivity, was significantly higher in the trained group (11.5 ± 1.1 mg.kg^-1.min^-1) than in the control group (6.1 + 0.6mg.kg^-1.min^-1; p<0.01). Detraining decreased GIR-L significantly, to 7.4 ± 0.5 (Day 7: p<0.01) and 7.4 ± 0.5 mg.kg^-1.min^-1 (Day 21: p < 0.05). Insulin responsiveness, assessed by response to a 26.4 mU-dose of insulin (GIR-H), was also increased by training, from 21.8 ± 1.2 mg.kg^-1.min^-1 (control) to 32.9 ± 1.2 (Day 1, p < 0.01). Seven days after cessation of training period the level was nearly identical (33.4 ± 1.0 mg.kg^-1.min^-1) and remained high 3 weeks after training (30.8 ± 1.0: p<0.01, vs control). These data indicate that insulin responsiveness remains elevated for 3 weeks after training, although insulin sensitivity is reversed within seven days. These results may be attributed to changes in body composition or long-lasting changes in post-receptor mechanisms.