Long-term exercise training with constant energy intake. 2: Effect on glucose metabolism and resting energy expenditure.

The effect of exercise training on glucose and insulin metabolism as well as on resting energy expenditure was investigated in five young men (mean BMI = 27.5 +/- 2.9 (s.d)). Subjects performed cycle-ergometer exercise 6 days/week over a 100 day period and the quantity of daily exercise was calculated to induce a 4.2 MJ/day surplus in energy expenditure during the days of training. As expected, significant weight and fat losses were observed in response to the training program. Exercise training induced a significant reduction in fasting levels and in the responses of insulin to a 4.2 MJ meal or an oral glucose load. Most of the training effects were noted after only 25 days of training. However, a significant decrease in plasma C-peptide concentrations during the oral glucose tolerance test was observed only at the end of the exercise program whereas essentially no change occurred during the first 25 days of training. The resting metabolic rate (RMR) and the thermic effect of food (TEF) were not significantly modified by training. Results show that the reduction in plasma insulin induced by training occurred earlier than that for C-peptide. Moreover, the absence of change in RMR in the presence of a substantial weight loss may represent a beneficial effect of training in comparison to the documented effect of diet-induced weight loss on RMR.