Effects of physical inactivity on skeletal muscle metabolic function

Being confined to bed rest has negative physiological consequences. Bed rest represents a unique model of physical inactivity and results in changes in cardiovascular, neural and metabolic function. In particular, reduced skeletal muscle mitochondrial capacity and a reduction in intrinsic mitochondrial function in response to physical inactivity may have broad implications for human disease. The aim of the present study was to test the hypothesis that physical inactivity, through the model of bed rest, will decrease mitochondrial function, insulin sensitivity and muscle mass in healthy young men. A reduction in lean muscle mass was evident after bed rest (p<0.05). This was accompanied by a reduction in skeletal muscle insulin sensitivity (p<0.05). Citrate synthase as a marker of mitochondrial content was reduced after bed rest (p<0.05). O2 flux expressed per mg of wet weight of muscle tissue was lower during LEAK respiration following 21 days of BR (p<0.05). OXPHOS and ETS capacity, indicative of maximal capacity, were increased following bed rest when normalized to citrate synthase activity (p