Interaction of exercise and age on substrates of carbohydrate metabolism.

Changes in blood lactate, pyruvate, glucose and tissue glycogen were used as indices to evaluate the extent of effects of physical conditioning in young and old male rats. Rats were trained on a running wheel and swimming tank for 10 weeks. Biochemical estimations of lactic acid (LA) pyruvic acid (PA) and glucose (GL) in plasma and glycogen in cardiac and slow-twitch soleus (SOL) and fast-twitch extensor digitorum longus (EDL) skeletal muscles of trained animals were conducted and compared with those of sedentary control rats. Blood parameters showed a decrease upon training in both young and old rats, though of variable significances, between exercise types. Glycogen levels in the cardiac and skeletal muscles increased in all groups with the exception in SOL of older trained animals. Hepatic glycogen exhibited an insignificant increase in all groups. Results suggest that, though the trends of responses of both young and old rats to exercise follow a comparable path, the magnitudes of changes are definitely impressed upon appreciably by increasing age.