Effect of the volume and intensity of exercise training on insulin sensitivity

Physical activity enhances insulin action in obese/overweight individuals. However, the exercise prescription required for the optimal enhancement is not known. The purpose of this study was to test the hypothesis that exercise training consisting of vigorous- intensity activity would enhance insulin sensitivity more substantially than moderate-intensity activity. Sedentary, overweight/obese subjects ( n = 154) were randomly assigned to either control or an exercise group for 6 mo: 1) low-volume/moderate-intensity group [ similar to 12 miles walking/wk at 40 - 55% peak O-2 consumption ((V) over dot O-2 peak)], 2) low-volume/high-intensity group (similar to 12 miles jogging/ wk at 65 - 80% (V) over dot O-2 peak), and 3) high-volume/ high-intensity group ( similar to 20 miles jogging/ wk at 65 - 80% V. O2 peak). Training volume (miles/wk) was achieved by exercising similar to 115 min/wk (low-volume/ high-intensity group) or similar to 170 min/wk (low-volume/ moderate-intensity and high-volume/ high-intensity groups). Insulin action was measured with an insulin sensitivity index ( SI) from an intravenous glucose tolerance test. In the control group, there was a decrement ( P < 0.05) in S-I. In contrast, all the exercise groups significantly (P < 0.05) increased SI; the relative increment in the low-volume/ moderate-intensity and high-volume/ high-intensity groups ( similar to 85%) were greater than in the low-volume/ high-intensity group ( similar to 40%). In conclusion, physical activity encompassing a wide range of intensity and volume minimizes the insulin resistance that develops with a sedentary lifestyle. However, an exercise prescription that incorporated similar to 170 min of exercise/wk improved insulin sensitivity more substantially than a program utilizing similar to 115 min of exercise/wk, regardless of exercise intensity and volume. Total exercise duration should thus be considered when designing training programs with the intent of improving insulin action.