The relationship between muscle mass and muscle strength in the elderly.

To determine the extent that muscle mass is predictive of muscle strength in the elderly, anthropomorphic estimates of muscle area and impedance measurements of muscle mass and peak isometric muscle strength were obtained in a relatively healthy older population over 65 years of age (mean age = 71.7; n = 218). Midarm muscle area correlated strongly with upper arm strength (r = 0.68, P less than 0.0001) while midthigh muscle area had a much lower correlation with thigh muscle strength (r = 0.29, P less than 0.0001). These muscle area calculations also include bone area. Lean body mass calculated by bioelectric impedance correlated highly with cumulative muscle strength measured by summing all muscle groups (r = 0.79, P less than 0.0001). To determine whether aging alters muscle strength per unit of muscle mass, additional middle-aged subjects were included, and three groups, middle-aged (55-64) (n = 78), young-old (65-74) (n = 161), and old-old (75+) (n = 57), were compared. A significant age-related trend of decreasing muscle strength per unit of lean body mass was noted. It is concluded that although muscle mass correlates with muscle strength in a healthy older population, use of simple age-independent clinical measurements of body mass should not be used to predict muscle strength.