Purpose: To evaluate the accuracy of ultrasound (ULTRA) in assessing fat-free mass (FFM) in comparison with hydrostatic weighing (HW) and skinfolds (SK) in high school wrestlers in a hydrated state.
Methods: Body composition was determined by ULTRA, HW, and three-site SK in 70 high school wrestlers (mean ± SD: age, 15.5 ± 1.5; height, 1.60 ± 0.08 m; body mass, 65.8 ± 12.7 kg). For all methods, body density (Db) was converted to percent body fat (%BF) using the Brozek equation. Hydration state was quantified by evaluating urine specific gravity.
Results: There were no significant differences for estimated FFM between ULTRA (57.2 ± 9.7 kg) and HW (57.0 ± 9.9 kg); however, SK (54.9 ± 8.8 kg) were significantly different from HW. The standard errors of estimate for FFM with HW as the reference method were 2.40 kg for ULTRA and 2.74 kg for SK. Significant correlations were found for FFM between HW and ULTRA (r = 0.97, P < 0.001) and between HW and SK (r = 0.96, P < 0.001). A systematic bias was found for SK, as the difference between SK and HW significantly correlated with the FFM average of the two methods (r = −0.38, P < 0.001). This systematic bias was not found for ULTRA (r = − 0.07).
Conclusions: This study demonstrates that ULTRA provides similar estimates of FFM when compared with HW in a heterogeneous high school wrestling population during a hydrated state. ULTRA should be considered as an alternative field-based method of estimating the FFM of high school wrestlers.