Validity of surface anthropometry to estimate upper-arm muscularity, including changes with body mass loss.

The differences among fatfold thicknesses, girths, and muscle plus bone cross-sectional area (M+B CSA) were examined at three sites along the upper arm (distal, mid, and proximal) by using surface anthropometry (study 1, n = 40) and x ray (study 2, n = 53). Changes in anthropometry and x ray were also evaluated in nine obese patients who reduced body mass by less than or equal to 20.5 kg over 32 wk. Weight reduction resulted in nonproportional changes at the three sites, including significant differences in M+B CSA. Thus, it would not be valid to consider the arm as a geometric cylinder. Although a one-time assessment of upper arm M+B CSA with surface anthropometry may be valid at any of the three sites, changes in M+B CSA measured at any site may result in an under- or overestimation of actual changes in M+B CSA.