As exercise training improves insulin sensitivity, the purpose of this study was to understand its effect on β-cell function. A total of 260 sedentary, overweight adults took part in the study and were randomized to one of the three 8-month exercise programs: 1) low amount/moderate intensity, 2) low amount/vigorous intensity or 3) high amount/vigorous intensity. Disposition index (DI) (insulin sensitivity x insulin response to glucose) was used to reflect β-cell function and predict development of type 2 diabetes. Overall, all three exercise groups showed an increased DI but the greatest increase was observed in the moderate intensity group. Interestingly, the high amount/vigorous intensity exercise training was associated with improvement in insulin sensitivity and a compensatory decrease in insulin secretion while low amount/moderate intensity exercise training induced a similar improvement in insulin sensitivity but with almost no reduction in insulin secretion. On the other hand, the inactive control group experienced a significant increase in fasting glucose indicating a progression toward type 2 diabetes. While moderate intensity exercise led to the greatest improvement in DI, which may reflect a transition towards a more normal DI, long term investigations will be necessary to determine which is the most effective exercise form to reduce type 2 diabetes risk.
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