Bioelectrical impedance vector analysis and phase angle in response to resistance training volume reduction in older women

BACKGROUND Bioelectrical impedance vector analysis (BIVA) and phase angle (PhA) are important for monitoring hydration, muscle function, and quality of life in older adults. Resistance training (RT) can counteract aging's adverse effects on cellular integrity and function. OBJECTIVE This study compared the effects of RT volume reduction on BIVA and PhA in physically independent older women. Sixty-seven participants (> 60 years) underwent a 20-week standardized whole-body RT program (eight exercises, three sets each, three non-consecutive days per week). They were then randomly assigned to one of three eight-week training conditions: reduced volume to one set (RV1, n = 22), two sets (RV2, n = 24), or maintained volume (MV, n = 21). Bioimpedance spectroscopy measured total body water (TBW), intracellular (ICW), and extracellular (ECW) water, BIVA, and PhA based on resistance (R), impedance (Z), reactance (Xc), and height (H). All groups showed significant increases in TBW, ICW, and ECW during the volume reduction phase (P < 0.05). RESULTS R, R/H, Z, and Z/H decreased across all groups, with significant changes from the pre-conditioning phase in the RV1 and RV2 groups (P < 0.05). Xc and Xc/H increased during the pre-conditioning phase across all groups and returned to baseline during the volume reduction phase (P < 0.05). PhA increased during the pre-conditioning and was maintained during the volume reduction phase (RV1 = + 0.33°, RV2 = + 0.50°, MV = + 0.47°; P < 0.05). CONCLUSION These results suggest that reducing RT volume by up to one-third can still improve PhA, BIVA, and hydration status in older women.