Association between phase angle and isolated and grouped physical fitness indicators in adolescents

Objective: Examine association between phase angle and isolated and grouped physical fitness indicators in adolescents. Methods: The sample consisted of 353 adolescents, aged 10-16 years. Phase angle was calculated based on crude resistance and reactance values (50 kHz frequency) obtained by tetrapole electrical bioimpedance (BIA). Fat mass and lean mass were estimated by means of anthropometric equations. Hydraulic dynamometer was used to measure handgrip strength and aerobic fitness was obtained by means of the 20-m back-and-forth test. The z-score for isolated and grouped physical fitness indicators was calculated. Covariates were age, habitual physical activity and screen time (obtained by questionnaire), and sexual maturation (self-reported). Results: For males, phase angle was directly associated with lean mass (beta = 0.02, p < 0.01), handgrip strength (beta = 0.03, p < 0.01), and aerobic fitness (beta = 0.01, p = 0.05), even adjusting for covariates. For females, phase angle was directly associated with lean mass (beta = 0.02; p = 0.04) after adjusting for covariates. Phase angle was directly associated with composite physical fitness z-score in both sexes (male, beta = 0.09, p < 0.01, female, beta = 0.03, p = 0.05), even adjusting for covariates. Conclusions: Phase angle was directly associated with isolated and grouped physical fitness indicators in adolescents. In this way, the phase angle can be used to monitor the health of adolescents.