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Improvement in insulin action following short-term exercise training: Effect of exercise or energy balance?

Steven E Black, University of Massachusetts Amherst


Short-term exercise training reduces insulin resistance and improves insulin action. The purpose of this research was to examine how short-term training, defined as 5–10 consecutive days of exercise, reduces insulin resistance. A preliminary study investigated the effects of short-term exercise training on substrate utilization during exercise to explore the relationship of fuel selection and insulin action. The primary study examined the role of energy balance in mediating improved insulin action following short-term exercise training and how that affected risk factors for type 2 diabetes and cardiovascular disease. Prior to this study, the importance of generating a caloric deficit was unclear. Replacing the energy expended during exercise to prevent negative energy balance might oppose the insulin-sensitizing effects of exercise. The purpose of this study was to establish the role of negative energy balance in mediating improved insulin action after short-term exercise training. Design. Previously sedentary, overweight/obese subjects were randomly placed in an energy balance group, in which energy expended during exercise was promptly replaced (BAL, n = 8) or in a caloric deficit group in which the energy was not replaced (NEG, n = 8). The groups were similar at baseline in age, BMI, trunk fat, lean mass, VO2 peak and insulin resistance. Training consisted of 6 consecutive days of treadmill walking (60–65% VO2 peak) to expend ∼500 kcals (duration = 62 ± 6.5 min/d). Insulin action pre- and post-training was measured by glucose rate of disappearance per unit insulin. Results. As designed, daily energy expenditure increased by ∼500 kcal/d during training in each group (NEG = 469 ± 45, BAL = 521 ± 48). Insulin action increased 40% in NEG (p = 0.032) but was unchanged in BAL (−8.4%, p = 0.107). Suppression of hepatic glucose production during the glucose infusion increased significantly only in NEG (+30.2 ± 9.5%, p = 0.037) but not in BAL (−10.0 ± 7.4%, p = 0.417). Mean changes in fasting plasma insulin, leptin, triglycerides, adiponectin and C-reactive protein tracked charges in insulin action but only changes in leptin were statistically significant. Conclusions. Short-term exercise training without energy replacement significantly reduced insulin resistance. Feeding back the 500 kcal of energy expended during exercise negated the effect of training. These findings suggest that subtle changes in energy balance that precede measurable fat loss play a key role in mediating the beneficial effects of exercise on whole-body insulin action.

Subject Area

Nutrition|Sports medicine

Recommended Citation

Black, Steven E, "Improvement in insulin action following short-term exercise training: Effect of exercise or energy balance?" (2004). Doctoral Dissertations Available from Proquest. AAI3152674.