The interaction of aging and endurance exercise upon the mitochondrial function of skeletal muscle.

Mitochondrial function was determined in sedentary-control animals, 150, 300 and 720 days of age, and in endurance-trained animals 300 and 720 days of age. The mitochondria were isolated from two regions of the cell of the gastrocnemius-plantaris muscle, subsarcolemmal and intermyofibrillar. State 3 respiration did not change with increasing age in control animals, but endurance training enhanced state 3 respiration in both the 300 and 720 day old trained animals. Age decreased the amount of intermyofibrillar mitochondrial protein, while training increased the mitochondrial protein of both regions of the cell. The decrease in oxidative metabolism in the skeletal muscle resulted from a decrease in mitochondrial protein, not to a decrease on mitochondrial function.