Objective To compare multiple body composition analysis methods in athletes with varying states of hydration to the criterion 5-compartment model(5CM) of body composition and assess the relationships of technique-specific estimates of fat and fat-free mass(FM, FFM) to muscle strength. Methods Body composition was assessed in 80(40-female) athletes with a mean age of 21.84.2 years. All athletes underwent laboratory-based methods: air-displacement plethysmography(ADP), deuterium-oxide dilution(D2O), dual-energy X-ray absorptiometry(DXA), underwater-weighing(UWW), and field-based: 3D-optical(3DO) imaging, and three bioelectrical impedance(BIA) devices(S10/SFB7/SOZO). Participants muscular strength was assessed by isokinetic/isometric dynamometry. Accuracy was assessed by Lins concordance correlation coefficient(CCC) and precision by root-mean-square coefficient of variation(RMS-CV%). Results Athletes hydration status(total body water/FFM) was significantly(p<0.05) outside of the normal range in both males(0.63-0.73%) and females(0.58-0.78%). The most accurate techniques(ADP/DXA) showed moderate-substantial agreement(CCC=0.90-0.95) in FM and FFM, whereas all field assessments had poor agreement(CCC<0.90), except 3DO FFM in females(CCC=0.91). All measures of FFM produced excellent <1.0% precision, whereas FM from ADP, DXA, D2O, S10, and UWW had <2.0%. The associations between muscle strength and the various devices FFM estimates differed. However, more accurate body composition compared to the criterion produced a better determination of muscle strength by significant quartile p-trends(p<0.001). The 5CM exhibits the highest determination for all categories of muscle strength which persisted across all hydration measures. Conclusion To optimize accuracy in assessing body composition and muscle strength, researchers and clinicians should prioritize selecting devices based on their accuracy compared to the 5CM. Reliable approaches such as ADP and DXA yield accurate and precise body composition estimates and thereby, better strength assessments, regardless of hydration status. Future athlete studies should investigate the impact of changes in FFM on functional measures compared to the criterion method.

The authors have declared no competing interest.

This study was funded by Hologic Inc. grant # 2018-01102.

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