Physical activity, protein intake, and appendicular skeletal muscle mass in older men.

BACKGROUND: Aging is associated with physical inactivity, low energy intake, and loss of skeletal muscle mass. It is not clear whether regular physical activity and adequate dietary protein intake can attenuate the loss of skeletal muscle mass. OBJECTIVE: We hypothesized that the maintenance of physical activity and dietary protein intake would attenuate the age-related decline in total appendicular skeletal muscle mass. DESIGN: Total appendicular skeletal muscle mass was determined by dual-energy X-ray absorptiometry in 44 healthy, older white men aged 49-85 y. Physical activity level was determined by using a uniaxial accelerometer over a 9-d period. Dietary protein intake was estimated from a 3-d food record. RESULTS: Aging was inversely associated with total appendicular skeletal muscle mass in older men (r = -0.43; slope: -0. 119 +/- 0.039 kg/y; P < 0.01). An effect of age on appendicular skeletal muscle mass persisted after standing height and physical activity were controlled for (r = -0.34; slope: -0.120 +/- 0.052 kg/y; P = 0.03). Furthermore, an effect of age on appendicular skeletal muscle mass persisted after standing height and dietary protein intake per kilogram body mass was controlled for (r = -0.41; slope: -0.127 +/- 0.045 kg/y; P < 0.01). CONCLUSIONS: Maintaining regular physical activity and adequate protein intake may not offset the age-related loss of appendicular skeletal muscle mass in older men. Prospective studies are needed to confirm these results and to determine whether anabolic physical activity (eg, strength training) can attenuate the age-related loss of muscle mass in the elderly.