Domain-Specific Associations of Physical Activity With Phase Angle and Extracellular Water–to–Total Body Water Ratio in Middle-Aged or Older Adults: Cross-Sectional Study

Abstract Background The phase angle (PhA) and extracellular water (ECW)–to–total body water (TBW) ratio serve as indicators of cell membrane integrity and body fluid balance in older adults. Objective This study examined the domain-specific associations of physical activity (PA) with PhA and the ECW-to-TBW ratio. Methods A nationally representative sample of 5211 adults aged 50 years and older was analyzed. Weekly amounts of moderate-to-vigorous PA (MVPA) in leisure-time, occupational, and transport-related domains were assessed using the Global Physical Activity Questionnaire. A bioelectrical impedance analyzer was used to measure PhA (°) and the ECW-to-TBW ratio (%). Linear regression analyses were conducted. Results For leisure-time PA, compared with 0 min/week, participating in 150 to 299 min/week and ≥300 min/week of MVPA was associated with 0.08 (95% CI 0.02-0.14) and 0.13 (95% CI 0.06-0.20) degrees higher PhA, respectively. Additionally, compared with 0 min/week, engaging in 150 to 299 min/week and ≥300 min/week of MVPA was associated with –0.11 (95% CI –0.19 to –0.03) and –0.15 (95% CI –0.22 to –0.07) percentage points lower ECW-to-TBW ratio, respectively. For transport-related PA, compared with 0 min/week, engaging in ≥300 min/week of MVPA was negatively associated with the ECW-to-TBW ratio (β=–0.07, 95% CI –0.14 to –0.01). Occupational PA showed no clear associations with PhA or the ECW-to-TBW ratio. Conclusions While the observed associations were modest, the associations of PA with both PhA and the ECW-to-TBW ratio differed across PA domains. Specifically, leisure-time PA was positively associated with PhA and inversely associated with the ECW-to-TBW ratio. These findings highlight the potential role of leisure-time PA in improving bioelectrical markers of cellular health and fluid distribution.