High Oxidative Capacity Due to Chronic Exercise Training Attenuates Lipid-Induced Insulin Resistance

Fat accumulation in skeletal muscle combined with low mitochon-drial oxidative capacity is associated with insulin resistance (IR). Endurance-trained athletes, characterized by a high oxidative ca-pacity, have elevated intramyocellular lipids, yet are highly insulin sensitive. We tested the hypothesis that a high oxidative capacity could attenuate lipid-induced IR. Nine endurance-trained (age = 23.46 0.9 years; BMI = 21.26 0.6 kg/m2) and 10 untrained subjects (age = 21.96 0.9 years; BMI = 22.86 0.6 kg/m2) were included and underwent a clamp with either infusion of glycerol or intralipid. Muscle biopsies were taken to perform high-resolution respirome-try and protein phosphorylation/expression. Trained subjects had;32 % higher mitochondrial capacity and;22 % higher insulin sen-sitivity (P, 0.05 for both). Lipid infusion reduced insulin-stimulated glucose uptake by 63 % in untrained subjects (P, 0.05), whereas this effect was blunted in trained subjects (29%, P, 0.05). In untrained subjects, lipid infusion reduced oxidative and nonox