Insulin Signaling & Glucose Metabolism in Glycolytic & Oxidative Muscle of High Fat Fed & Endurance Trained

This study examines the effects of a chronic high-fat diet (HFD) and chronic endurance exercise (CEE) upon muscles of varying oxidative (Ox) and glycolytic capacities. We report that chronic HFD leads to significantly high levels of blood glucose and insulin concentrations. These high concentrations were due to the reduction in the activity of key proteins in the insulin-signaling (IS) cascade, leading to blunted rates of glycogen synthesis (GSR) and reduced glucose-6-phosphate (G6P) content in all muscles fiber types (MFTs) of HF-fed rodents. Conversely, CEE increased insulin sensitivity, increased GSR and G6P content. Our work has shown that hyperlipidemia causes all MFTs to develop insulin resistance regardless of Ox capacity. However, it appears that the Ox fibers are more severely affected by insulin resistance and that the pathogenesis of insulin resistance is different between muscle fiber types.