Accuracy and Precision of Multiple Laboratory and Field Methods to The Criterion In Vivo Five-Compartment Body Composition Model and Their Association with Muscle Strength in Collegiate Athletes of Varying States of Hydration: The Da Kine Protocol Study

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. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This study was funded by Hologic Inc. grant # 2018-01102. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The ethics committee/IRB of the University of Hawaii gave ethical approval for this work I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors