Phase Angle Differences by Self-Reported Leisure-Time Exercise Frequency and BMI Among Japanese Males Aged 15–17 Years

Background: This cross-sectional study investigated the relationship between leisure-time exercise frequency and physical characteristics such as phase angle (PhA) measured by bioelectrical impedance analysis in high-school boys. Methods: A total of 355 participants completed a questionnaire about their exercise habits outside of physical education classes, and their body size and composition were measured. Exercise frequency was categorized as follows: (1) ≥3 days/week; (2) 1–2 days/week; (3) 1–3 days/month; and (4) never. Participants in group (1) were further subdivided based on whether a single exercise session lasted ≥2 hours. Logistic regression analysis was used to assess the association between exercise frequency categories and age, body mass index (BMI) and PhA. Results: PhA was significantly higher in those exercising ≥1 day/week and, among those exercising ≥3 days/week, in those with longer exercise sessions (P< 0.05, d = 0.45–0.58). No significant differences were observed in height, body mass, BMI, fat mass, or fat-free mass. Logistic regression analysis revealed that PhA was significantly associated with exercise frequency, with an odds ratio of 4.43 (95% confidence interval: 2.87–6.83). These results suggest that self-reported leisure-time exercise frequency and session duration are associated with differences in PhA that may not be apparent from body size or composition. However, BMI was significantly and positively associated with PhA within a similar exercise frequency range. Conclusions: These results suggest that PhA varies between categories of self-reported leisure-time exercise frequency and session duration, while BMI and growth-related factors may complicate the interpretation of these variations.