Concerns over the Utility of Phase Angle and its Association with Muscle Function

Abstract

Introduction: Phase angle (PhA) derived from bioelectrical impedance analysis (BIA) has been used as an indicator of cellular hydration, muscle function, and nutritional status. Positive relationships between PhA and various measures of muscle function have been reported but it remains unclear whether PhA retains its predictive utility of muscle function, or whether it performs better than fat-free mass (FFM) in the context of muscle function. Methods: This perspective highlights secondary analyses of data collected during a randomized, double-blind, placebo-controlled trial that examined indices of recovery with different whey protein supplements after muscle-damaging exercise among resistance-trained adults. Results: Bivariate correlations between phase angle and quadriceps twitch force were positively correlated at baseline, 24-h, and 72-h post-exercise. In linear regression, FFM was shown to account for nearly 44% (partial r = 0.662) of the variance in quadriceps twitch force independent of phase angle at 24-h. A similar pattern emerged at 48-h and 72-h post-exercise Conclusions: Within this framework, these data demonstrate that: 1) PhA exhibits a weaker correlation to quadriceps twitch force compared to FFM and 2) in the context of muscle function, PhA does not provide additional information beyond that of FFM alone. Investigators should consider adjusting for FFM when evaluating the relationship between PhA and muscle function outcomes.