Appendicular skeletal muscle mass: effects of age, gender, and ethnicity

Gallagher, Dympna, Marjolein Visser, Ronald E. De Meersman,Dennis Sepúlveda, Richard N. Baumgartner, Richard N. Pierson, Tamara Harris, and Steven B. Heymsfield. Appendicular skeletal muscle mass: effects of age, gender, and ethnicity. J. Appl. Physiol. 83(1): 229-239, 1997.This studytested the hypothesis that skeletal muscle mass is reduced in elderlywomen and men after adjustment first for stature and body weight. Thehypothesis was evaluated by estimating appendicular skeletal musclemass with dual-energy X-ray absorptiometry in a healthy adult cohort. Asecond purpose was to test the hypothesis that whole body⁴⁰K counting-derived total bodypotassium (TBK) is a reliable indirect measure of skeletal muscle mass.The independent effects on both appendicular skeletal muscle and TBK ofgender (n = 148 women and 136 men) andethnicity (n = 152 African-Americans and 132 Caucasians) were also explored. Main findingswere 1) for both appendicularskeletal muscle mass (total, leg, and arm) and TBK, age was anindependent determinant after adjustment first by stepwise multipleregression for stature and weight (multiple regression modelr² = ~0.60);absolute decrease with greater age in men was almost double that inwomen; significantly larger absolute amounts were observed in men andAfrican-Americans after adjustment first for stature, weight, and age;and >80% of within-gender or -ethnic group between-individualcomponent variation was explained by stature, weight, age, gender, andethnicity differences; and 2) mostof between-individual TBK variation could be explained by totalappendicular skeletal muscle(r² = 0.865),whereas age, gender, and ethnicity were small but significant additional covariates (totalr² = 0.903). Ourstudy supports the hypotheses that skeletal muscle is reduced in theelderly and that TBK provides a reasonable indirect assessment ofskeletal muscle mass. These findings provide a foundation forinvestigating skeletal muscle mass in a wide range of health-related conditions.