David Looney ^1,2,3 Erica A Schafer ^1,4 Christopher Chapman ^1,4 Riana Pryor ⁵ Adam W Potter ^1* Brandon M Roberts ¹ Karl E Friedl ¹

• ¹ US Army Research Institute of Environmental Medicine (USARIEM), Natick, United States
• ² Maximize Human Performance, LLC, Framingham, MA, United States
• ³ CoachMePlus, Buffalo, NY, United States
• ⁴ Oak Ridge Institute for Science and Education (ORISE), Oak Ridge, Tennessee, United States
• ⁵ Center for Research and Education in Special Environments, Department of Exercise and Nutrition Sciences, School of Public Health and Health Professions, University at Buffalo, Buffalo, New York, United States

Introduction: Bioelectrical impedance analysis (BIA) systems are gaining popularity for use in research and fitness assessments as the technology improves and becomes more affordable and easier to use. Multifrequency BIA (MF-BIA) may improve accuracy and precision using octopolar contacts for segmental analyses. Purpose: Evaluate reliability, biological variability, and accuracy of component measures (total body water, mass, and composition) of commercially available MF-BIA system (InBody 770, Cerritos, California, USA). Methods: Fourteen healthy military-age adults were assessed by MF-BIA in duplicate on five laboratory visits across 3 weeks (10 measures each). Participants were evaluated at the same time of day after refraining from strenuous exercise (> 48 h), alcohol consumption (> 24 h), and caffeine, nicotine, and food (> 10 h). Systematic error (test-retest reliability) and biological variability (day-to-day reliability) were summarized by intraclass correlation coefficient (ICC) values determined for body mass (fat, fat-free, total) and body water (extracellular, intracellular, total). Body composition measurements derived from BIA on the second visit were also tested for accuracy compared to dual-energy x-ray absorptiometry (DXA). Results: Test-retest reliability was very high for all measurements of whole-body water and mass (ICC ≥ 0.999) and high for regional body water and mass (ICC 0.973–1.000). Biological variability was observable with very minor differences between tests (same day) for total and regional body water (0.0–0.2L) and total and regional body mass measurements (0.0–0.2kg); while between day differences were slightly higher (0.0–0.5L and 0.1–0.7kg). Compared to DXA, the MF-BIA whole-body measures showed an offset in %BF (Bias −4.0 ± 2.8%; Standard error of the estimate (SEE), 2.6%), an overprediction for total body fat-free mass (Bias 2.8±2.1kg; SEE 2.2%) and an underprediction of total body fat mass (Bias −2.9±2.0kg; SEE 1.9%). Conclusion: Under controlled conditions with fit and healthy men and women, this MF-BIA system has high methodological reliability and demonstrates stable day-to-day measurements of major body composition components. Previously reported ~3% body fat offset compared to criterion methods was again confirmed. Precision of the InBody 770 shows consistency and supports further testing of this specific device as a new military standards method and suitability across a wider range of %BF.