Abstract

OBJECTIVES: To determine whether lower lean mass and higher fat mass have independent effects on the loss of strength and muscle quality in older adults and might explain part of the effect of age. DESIGN: Single‐episode, cross‐sectional analyses of a cohort of subjects in the Health, Aging and Body Composition (Health ABC) Study. SETTING: Ambulatory clinic and research laboratory. PARTICIPANTS: Two thousand six hundred twenty‐three men and women aged 70 to 79 from the Health ABC Study. MEASUREMENTS: Upper and lower extremity strength was measured using isokinetic (knee extension) and isometric (grip strength) dynamometers. Body composition (lean mass and fat mass) was determined by measuring lean mass of upper and lower extremities and the total body by dual‐energy x‐ray absorptiometry. Muscle quality was ascertained by taking the ratio of strength to muscle mass for both upper and lower extremities. RESULTS: Upper and lower extremity strength and muscle quality decreased as age increased. Most of the explained variance in strength was due to differences in muscle mass, but, in those at the extremes of body fat and lower leg muscle quality, the association with body fat was independent of the effect of age. Although blacks had greater muscle strength and mass than whites, leg muscle quality tended to be lower in blacks than in whites. Upper extremity strength adjusted for lean mass and muscle quality were also associated inversely and independently with age, body fat, and black race. CONCLUSION: In this older cohort, lower strength with older age was predominantly due to a lower muscle mass. Age and body fat also had significant inverse associations with strength and muscle quality. Both preservation of lean mass and prevention of gain in fat may be important in maintaining strength and muscle quality in old age.