Smartwatch-based bioimpedance analysis for body composition estimation: Precision and agreement with a 4-compartment model.

Given that the prevalence of smartwatches has allowed them to become a hallmark in health monitoring, this technology is primed to provide accessible body composition estimations. The purpose of this study was to evaluate the precision and agreement of smartwatch-based bioimpedance analysis and multifrequency bioimpedance analysis to a 4-compartment model criterion. A total of 186 participants (114 F) underwent body composition assessments necessary for a 4-compartment model and smartwatch and multifrequency bioimpedance analysis. Total body water from each device were also compared to bioimpedance spectroscopy. Precision was adequate though slightly lower for the smartwatch compared to other methods. No device demonstrated equivalence with the 4-compartment model. Specifically, the smartwatch overestimated and multifrequency underestimated body fat. Multifrequency bioimpedance analysis, but not smartwatch bioimpedance analysis, demonstrated equivalence for total body water. Overall error was higher for males using the smartwatch compared to females. While these findings do not invalidate the use of smartwatch-based estimates, clinicians should consider that there may be large errors relative to clinical measures. If this wearable device is intended to be used to monitor body composition change over time, these findings demonstrate the need for future research to evaluate its accuracy during follow-up testing.