Abstract

Objective: Insulin resistance and beta cell dysfunction both are important contributors to the pathogenesis of type 2 diabetes. Exercise training improves insulin sensitivity, but its effects on beta cell function are less well studied.

Methods: Sedentary, overweight adults were randomized to control or one of three eight-month exercise programs: 1) low-amount/moderate-intensity; 2) low-amount/vigorous-intensity; or 3) high-amount/vigorous-intensity. Of 387 randomized, 260 completed the study and 237 had complete data. Insulin sensitivity (SI), acute insulin response to glucose (AIRg) and the Disposition Index (DI = SI × AIRg) were modeled from an intravenous glucose tolerance test.

Results: Compared to controls, all three training programs led to increases in DI. However, the moderate-intensity group experienced a significantly larger increase in DI than either of the vigorous-intensity groups and through a different mechanism. The high-amount/vigorous-intensity group improved SI and had a compensatory reduction in AIRg, whereas the moderate-intensity group had a similar improvement in SI, but almost no reduction in AIRg. Importantly, the inactive control group experienced a significant increase in fasting glucose.

Conclusions: To the extent that the disposition index accurately reflects beta cell function, we observed that both moderate and vigorous intensity exercise-training improved beta cell function, albeit through distinct mechanisms. It is not clear which of these mechanisms is preferable for maintenance of metabolic health. While moderate-intensity exercise led to a larger improvement in DI, which may reflect a transition toward a more normal DI, longer term investigations would be necessary to determine which was more effective at reducing diabetes risk.