INFLUENCE OF AGE ON SKELETAL-MUSCLE GLUCOSE-TRANSPORT AND GLYCOGEN-METABOLISM

Age-related alterations in skeletal muscle carbohydrate metabolism can influence both health and performance. Exercising muscle glycogenolysis is accelerated in old, male rats compared with young animals, perhaps secondary to the age-related reduction in muscle oxidative capacity and blood flow during contractile activity. Muscle oxidative capacity and blood flow during exercise are also reduced in untrained older humans. Endurance training enhances muscle oxidative capacity and promotes muscle glycogen sparing during exercise by young and old rats. Resting muscle glycogen concentration is unchanged in old rats, but considerably reduced in untrained, older humans. Exercise training increases the muscle glycogen levels of older people. The concentration of GLUT-4 glucose transporter protein declines in some muscles of rats during growth and development, but remains stable thereafter. Exercise training can elevate the muscle GLUT-4 protein levels of both young and old humans. On the other hand, exercise training has been shown to increase the GLUT-4 values of adult, but not old rats. After one bout of exercise, muscle sensitivity for insulin-stimulated glucose transport is improved in young and old rats. These findings indicate that several age-related changes in muscle carbohydrate metabolism can be minimized by acute or chronic exercise.