Effects of habitual endurance and resistance exercise on insulin action in primary human skeletal muscle stem cells

Endurance-oriented exercise typically enhances insulin action in skeletal muscle; however, relatively little is known about the impact of resistance exercise. In the present study, insulin action was determined in primary human skeletal muscle stem cells (HSkMCs) isolated from habitual endurance and resistance exercisers and sedentary controls (N = 8–9/group). Insulin action was assessed by insulin-stimulated glycogen synthesis and glucose oxidation using 14C-labeled glucose and insulin signal transduction measured as phosphorylation of Akt (Ser⁴⁷³) and AS160 (Thr⁶⁴⁰). No differences were detected in basal and insulin-stimulated glycogen synthesis, glucose oxidation, and insulin signal transduction between the endurance and resistance exercisers. When HSkMCs were challenged by a fatty-acid treatment which induced insulin resistance, no differential protection was detected with either exercise training modality. When data from the habitual endurance and resistance exercise groups were combined (EX) and compared to sedentary controls, HSkMC from EX exhibited greater rates of insulin-stimulated glycogen synthesis. However, Akt and AS160 phosphorylation were similar between EX and sedentary individuals. Exercise training provided no protection against fatty-acid-induced insulin resistance across any measure of insulin action. These data suggest that habitual exercise, including resistance training, improves insulin action in skeletal muscle but may not offer intrinsic protection against fatty-acid-induced insulin resistance.