Abstract
Defects in insulin sensitivity are associated with metabolic inflexibility and obesity albeit some obese subjects have preserved insulin sensitivity. A decrease in lipid oxidation during exercise can be found in obesity and type 2 diabetes. This lipid oxidation capacity has been found to be associated in healthy or overweight subjects with insulin sensitivity and mitochondrial function. Thus, we aimed at delineate the interrelationships among the maximal ability to oxidize lipids at exercise (LIPOXmax) insulin sensitivity and mitochondrial function in middle-aged obese men with different levels of insulin sensitivity.After an overnight fast, twenty middle-aged male obese subjects performed: a maximal incremental exercise test allowing the determination of LIPOXmax, two days after a measurement of insulin sensitivity and two days after a muscle biopsy for mitochondrial respiration.According to the minimal model, we found 9 insulin-resistant and 11 insulin-sensitive middle-aged obese men. LIPOXmax (expressed as power intensity) and whole-body insulin sensitivity are significantly correlated in obese insulin-sensitive but not in insulin-resistant obese men. LIPOXmax and insulin sensitivity are correlated to mitochondrial pyruvate oxidation and mitochondrial density. Multivariate analysis indicates that insulin sensitivity is statistically better explained by the LIPOXmax which is in turn better explained by the mitochondrial function parameter Vmax/V0 pyruvate.Thus, insulin sensitivity, mitochondrial function and the ability of muscle to oxidize lipids during exercise are three closely correlated parameters in middle-aged male obese insulin-sensitive patients.