Context: Short-term aerobic exercise training can improve whole-body insulin sensitivity in humans with type 2 diabetes mellitus, however the contributions of peripheral and hepatic tissues to these improvements are not known.

Objective: To determine the effect of seven days of aerobic exercise on peripheral and hepatic insulin sensitivity during isoglycemic/hyperinsulinemic clamp conditions.

Design: Subjects were randomly assigned to one of two groups: the energy balance group consumed an isocaloric diet consisting of 50% carbohydrate, 30% fat, and 20% protein for 15 days. The energy balance plus exercise group consumed a similar diet over the 15 days and performed 50 minutes of treadmill walking at 70% of VO₂ maximum during the second seven days of the 15-day study period. Each subject underwent an initial isoglycemic/hyperinsulinemic clamp after one week of dietary control and a second clamp after completing the study.

Setting: The Ohio State University's General Clinical Research Center.

Participants: Eighteen obese, mildly diabetic humans.

Intervention: Seven days of aerobic exercise training.

Main Outcome Measures: Whole-body, peripheral and hepatic insulin sensitivity.

Results: Exercise training did not have an impact on peripheral glucose uptake or endogenous glucose production during the basal state or during low-dose insulin. Likewise, it did not alter endogenous glucose production during high-dose insulin. However, one week of exercise training increased both whole-body (p < 0.05) and peripheral insulin sensitivity (p < 0.0001) during high-dose insulin.

Conclusions: Improvements to insulin sensitivity after short-term aerobic exercise training are due to gains in peripheral, not hepatic insulin sensitivity.