Genetically determined exercise capacity affects systemic glucose response to insulin in rats

Aerobic exercise capacity is inversely related to morbidity and mortality as well as to insulin resistance. However, exercising in patients has led to conflicting results, presumably because aerobic exercise capacity consists of intrinsic (genetically determined) and extrinsic (environmentally determined) parts. The contribution of both parts to insulin sensitivity is also not clear. We investi-gated sedentary and exercised (aerobic interval training) high-capacity runners (HCR) and low-capacity runners (LCR) differing in their genetically determined aerobic exercise capacity to determine the contribution of both parts to insulin sensitivity. LCR and HCR differed in their untrained exercise capacity and body weight. Sedentary LCR displayed a diabetic phenotype with higher random glucose, lower glucose infusion rate during hyperinsulinemic euglycemic clamping than HCR. Echocardiography showed equal morphological and functional parameters and no change with exercise. Four week of exercise caused significant improvements in aerobic exercise capacity, which was more pronounced in LCR. However, with respect to glucose use, exercise affected HCR only. In these animals, exercise increased 2-deoxyglucose uptake in gastrocnemius ( þ 58.5%, P = 0.1) and in epi-didymal fat ( þ 106%; P < 0.05). Citrate synthase activity also increased in these tissues (gastrocnemius 69% epididymal fat 63%). In our model of HCR and LCR, genetic predisposition for low exercise capacity is associated with impaired insulin sensitivity and impedes exercise-induced improvements in insulin response. Our results suggest that genetic predisposition for low aerobic exercise capacity impairs insulin response, which may not be overcome by exercise.