Skinfold Thicknesses And Ultrasound Perform Similarly When Used For Correcting Girths To Estimate Fat-free Mass

Body composition is a fundamental component of fitness. Among the available techniques for body composition assessment (including fat-free mass, FFM), anthropometry offers portability, cost-effectiveness, and relative ease of application. Incorporating corrected girths for subcutaneous adipose tissue (SAT) is valuable for estimating FFM. However, the SAT estimated from skinfold thicknesses introduces theoretical weakness that ultrasound-measured SAT may potentially mitigate. PURPOSE: To determine whether the girths corrected for ultrasound-measured SAT are better to predict DXA-derived FFM than girths corrected for skinfold thickness-measured SAT. METHODS: Sixty university students (42 females, age: 21.3 ± 2.2 y, weight: 58.4 ± 10.3 kg, height: 1.61 ± 0.07 m, FFM: 41.9 ± 6.5 kg; 18 males, age: 21.2 ± 1.8 y, weight: 73.0 ± 11.7 kg, height: 1.76 ± 0.06 m, FFM: 61.4 ± 9.1 kg) underwent a whole-body DXA scan to assess their FFM, and anthropometric measurements according to the ISAK protocol carried out by certified personnel. We calculated four corrected girths (CG) as Girth - (π * SAT) for the arm, forearm, proximal thigh, and calf girths, corrected for the triceps, biceps, thigh, and calf SAT coming from anthropometric skinfold thicknesses or ultrasound images measured at the same location. Then, we calculated a corrected girth method (CGM) as the Average CG (cm) * Height (m), where the CG could come from anthropometry (CGM-A) or ultrasound (CGM-U). We used simple linear regression models to estimate DXA-derived FFM from CGM-A and CGM-U by sex. RESULTS: The mean CGM-A and CGM-U for females was 50.20 ± 5.33 and 53.24 ± 5.66, whereas for males they were 62.58 ± 6.89 and 64.63 ± 6.89, respectively. The prediction equations for females were: FFM = -16.08 + 1.15 * CGM-A (SEE = 2.09 kg, R2 = 0.90), and FFM = -15.93 + 1.09 * CGM-U (SEE = 2.09 kg, R2 = 0.90). The prediction equations for males were: FFM = -18.43 + 1.28 * CGM-A (SEE = 2.51 kg, R2 = 0.93), and FFM = -19.19 + 1.25 CGM-U (SEE = 2.60 kg, R2 = 0.92). CONCLUSIONS: The anthropometric and ultrasound CGM are valid FFM indicators; however, ultrasound does not improve the correlation with FFM compared to anthropometry. More extensive and longitudinal studies are needed to validate our findings and assess the comparative efficacy in detecting changes in FFM.