Markers of mitochondrial biogenesis and metabolism are lower in overweight and obese insulinresistant subjects

Background: Impaired mitochondrial function in skeletal muscle is implicated in the development of insulin resistance. However, poten-tial differences in fatness and fitness may influence previous results. Methods: Subjects (n 18) were divided into insulin-sensitive (IS) and insulin-resistant (IR) groups by median glucose infusion rate during a hyperinsulinemic euglycemic clamp. Weight, VO2max (max-imal aerobic capacity), and percentage body fat weremeasured before and after 6 continuous weeks of aerobic exercise training at 55–70% VO2max (40 min/session, 4 d/wk). Results: Age, percentage fat, and VO2max were not different between IS and IR groups at baseline. Expression of the nuclear encoded PGC1 and mitochondrial encoded gene COX1 were significantly lower in the IR group (P 0.05). Citrate synthase activity and protein levels of subunits from complexes I and III of the respiratory chain were also lower in the IR group (P 0.05). Insulin sensitivity an