Physical activity improves insulin sensitivity and endothelial function. However, it is not clear whether there are also direct cardioprotective effects on cardiomyocytes. In the current study, we compared the effects of physical activity (treadmill training, 12 weeks) on cardiac and skeletal muscle in insulin sensitive and insulin resistant mice.

Pyruvate- and succinate-dependent respiration and complex I activity are reduced in IL-6-/- and ob/ob mice compared to C57/BL6 wild-type mice. Plasma insulin / free fatty acids as well as tissue triyglyceride content are increased in IL-6-/- and ob/ob. Physical activity results in a renormalization of mito. function in IL-6-/- and ob/ob mice. The expression of transcriptional regulators (e.g. NRF-1) and of transcripts of the mito. genome (e.g. ND5) is increased in the left ventricle (120-160%) as well as in skeletal muscle (150-250%) in all groups under physical activity. It also resulted in increased glucose uptake, activation of AMPK in both muscular tissues and reduction in plasma insulin / free fatty acids in C57/BL6 and IL-6-/- mice, but not in insulin resistant ob/ob mice.

The complex I deficiency in cardiac muscle of obese animals is corrected by treadmill training together with an increase in mito. biogenesis. This improvement of mito. function appears to be independent of the protective effect on insulin resistance.