Muscularity in adult humans: Proportion of adipose tissue-free body mass as skeletal muscle

Muscularity, or the proportion of adipose tissue-free body mass (ATFM) as s keletal muscle (SM), provides valuable body composition information, especi ally for age-related SM loss (i.e., sarcopenia). Limited data from elderly cadavers suggest a relatively constant SM/ATFM ratio, 0.540 +/- 0.046 for m en (mean +/- SD, n = 6) and 0.489 +/- 0.049 for women (n = 7). The aim of t he present study was to examine the magnitude and constancy of the SM/ATFM ratio in healthy adults. Whole-body SM and ATFM were measured using multi-s can magnetic resonance imaging. The SM/ATFM ratio was 0.528 +/- 0.036 for m en (n = 139) and 0.473 +/- 0.037 for women (n = 165). Multiple regression a nalysis indicated that the SM/ATFM ratio was significantly influenced by se x, age, body weight, and race. The four factors explained 50%, of the obser ved between individual variation in the SM/ATFM ratio. After adjusting for age, body weight, and race, men had a larger SM/ATFM ratio than women. Both older men and women had a lower SM/ATFM ratio than younger subjects, altho ugh the relative reduction was greater in men. After adjustment for sex, ag e, and body weight, there were no significant differences in the SM/ATFM ra tios between Asian, Caucasian, and Hispanic subjects. In contrast, African- American subjects had a significantly greater SM/ATFM ratio than subjects i n the other three groups. In addition, the SM/ATFM ratio was significantly lower in AIDS patients than corresponding values in healthy subjects. (C) 2 001 Wiley-Liss, Inc.