Body Water Distribution and Phase Angle Are Differentially Related to Anaerobic Performance by Occupational Status in...

Background: Bioimpedance-derived phase angle (PhA) and body water distribution may reflect cellular hydration and tissue quality, but their relevance to anaerobic performance in firefighters is unclear. Objectives: To compare these indices between firefighter recruits and incumbents and determine whether their relationships with anaerobic performance differed by occupational status. Methods: This retrospective cross-sectional study included recruits (n = 125) and incumbents (n = 71). Groups were compared for participant characteristics, bioimpedance variables, and Wingate performance. Pearson correlations and hierarchical regression tested relationships with relative peak (RelPP) and mean power (RelMP), including group × predictor interactions adjusted for fat mass (FM) and fat-free mass (FFM). Significance was set at p < 0.05. Results: Incumbents were older (38.89 ± 9.68 vs. 22.18 ± 4.47 years), heavier (95.14 ± 14.05 vs. 86.77 ± 13.72 kg), and had greater FM than recruits (p < 0.001). Recruits had higher RelPP and RelMP (p < 0.001), while body water distribution and PhA did not differ. In incumbents, intracellular water/total body water (ICW/TBW) and PhA were positively correlated with RelPP and RelMP, whereas extracellular water/total body water (ECW/TBW) was inversely correlated; these correlations were largely absent in recruits. After adjustment for FM and FFM, group × predictor interactions were observed for RelPP for PhA, ICW/TBW, ECW/TBW, and intracellular water/extracellular water (ICW/ECW) (p = 0.004-0.008), but not RelMP; these associations should be interpreted with caution given the number of comparisons examined. RelPP interactions remained significant after additional adjustment for age (p = 0.022-0.041). Conclusions: Despite similar body water distribution and PhA, recruits and incumbents differed in age, body mass, FM, and relative anaerobic performance. Occupational status appeared to moderate the relationships of these bioimpedance-derived indices with RelPP after adjustment for FM and FFM, with stronger relationships among incumbents.