Multiple-regression analysis in the present study demonstrated no significant differences in the SM/ATFM [skeletal muscle / adipose tissue-free body mass] ratio among Asian, Caucasian, and Hispanic healthy groups. In contrast, African-Americans had a significantly larger SM/ATFM ratio than the other groups, although the difference was very small. According to Equation 4, for example, the mean SM/ATFM ratio is 0.524 for a 30-year-old African-American man weighing 70 kg, while the mean ratio is 0.522 for Asian, Caucasian, and Hispanic men of the same age and body weight.Blacks probably carry a greater proportion of their muscle in their arms and legs (which is unsurprising considering they have relatively longer limbs), but total skeletal muscle mass is similar.
[Wang et al. Muscularity in adult humans: proportion of adipose tissue-free body mass as skeletal muscle. Am J Hum Biol. 2001 Sep-Oct;13(5):612-9.]
Overall, the matched Black and White men had similar fat, FFM, TBW, and TBK. Thus there were no major absolute differences in body composition between the two ethnic groups beyond that of skeletal mass.The evidence I've seen also suggests whites tend to have greater strength per unit of muscular cross-section than blacks. (Despite the fact that black males more frequently report lifting weights.)
In agreement with our findings, Schutte et al. (1984) found that Black and White males of equivalent height and weight had a similar absolute TBW. Slaughter et al. (1990) also found no significant ethnic differences in TBW adjusted for height among adolescent Black and White boys.
[. . .] Total body potassium is an indirect marker of skeletal muscle mass and results are therefore difficult to interpret. One possible explanation for the varied findings is that Black men may have more appendicular muscle and less trunk muscle than White men. According to this hypothesis, Black and White men would have different amounts of skeletal muscle in specific anatomic regions but similar amounts of total skeletal muscle.
[Gerace et al. Skeletal differences between black and white males and their relevance to body composition estimates. Am J Hum Biol 1994;6:255–62.]