Effects of Exercise Training on Glucose Homeostasis

In the absence of substantial weight loss, regular exercise is required for sustained improvements in glucose homeostasis.

To determine the effect of a 20-week endurance training program in healthy, previously sedentary participants on measures derived from an intravenous glucose tolerance test (IVGTT).

An IVGTT was performed before and after a standardized training program in 316 women and 280 men (173 blacks and 423 whites). Participants exercised on cycle ergometers 3 days per week for 60 sessions. The exercise intensity was progressively increased from 55% VO2max for 30 min per session to 75% VO2max for 50 min per session.

Mean insulin sensitivity increased by 10% (P < 0.001) following the intervention, but the variability in the changes was high. Men had larger improvements than women (P = 0.02). Improvements in fasting insulin were transitory, disappearing 72 h after the last bout of exercise. There were also significant mean increases in the glucose disappearance index (3%, P = 0.02) and in glucose effectiveness (11%, P < 0.001), measures of glucose tolerance and of the capacity of glucose to mediate its own disposal, respectively. The acute insulin response to glucose, a measure of insulin secretion, increased by 7% in the quartile with the lowest baseline glucose tolerance and decreased by 14% in the quartile with the highest baseline glucose tolerance (P < 0.001). The glucose area below fasting levels during the IVGTT was reduced by 7% (P = 0.02).

In conclusion, the absence of a nonexercise control group in the present study makes it difficult to obtain a precise estimate of the effect of structured regular exercise on the results on IVGTT-derived variables. However, although the effects of structured regular exercise were highly variable, there were improvements in virtually all IVGTT-derived variables. These improvements resulted in a better control of both high and low glucose levels and better overall glucose homeostasis. Men had larger improvements in insulin sensitivity than women, and participants with the lowest glucose tolerance showed an increase in insulin secretion following exercise training. Fasting insulin values suggest that the improvements in insulin sensitivity observed 24 h following an exercise session were transient, as they had disappeared after 72 h. Therefore, in the absence of substantial weight loss, regular exercise is required for sustained improvements in glucose homeostasis.

Diabetes Care 28:108-114, 2005

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