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. RESEARCH DESIGN AND METHODS: Sedentary, overweight adults were randomized to control or one of three 8-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 x AIRg) were modeled from an intravenous glucose tolerance test. RESULTS: Compared with control subjects, 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 DI 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.
Copyright American Diabetes Association. Reprinted with permission from The American Diabetes Association.

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