Changes in segmental bioimpedance following eccentric plantar flexor exercise taken to volitional failure

Segmental bioelectrical impedance analysis (BIA) evaluates cellular health through phase angle (PhA), resistance (R), and reactance (Xc), providing insights into localized muscle and fluid balance changes during exercise recovery. This exploratory study examined localized BIA responses following an eccentric plantar flexor exercise protocol combined with functional testing. Twenty male participants (82.6 ± 16 kg; 177 ± 8.7 cm; 23.8 ± 3.45 years) completed unilateral eccentric plantar flexor resistance training (40% of body mass as a weighted vest, four sets of fifty repetitions, fifth set to failure). One leg was trained (intervention), while the other served as a control. Pre-, immediate post-, and 24, 48, and 72 h post-exercise measurements included segmental intracellular water (ICW), extracellular water (ECW), R, Xc, and PhA at 50 kHz, impedance (Z at 5, 50, and 250 kHz) and impedance ratio (IR; 250/5 kHz). Two-way repeated measures ANOVA revealed significant leg-by-time interactions for all BIA parameters (p < 0.05), except for ECW, ICW, and Z, which had main effects for time (p > 0.05), and ECW/ICW which had no significant interaction or main effects. In the intervention leg, R (↓13.9 ± 6.8 Ω), IR (↑0.012 ± 0.006), and Xc (↓3.0 ± 1.6 Ω) changed immediately post-exercise (p < 0.001). PhA decreased immediately post (↓0.31 ± 0.18°) in the intervention leg, increased beyond baseline values at 24 h (↑0.33 ± 0.20°), and remained elevated at 48 h (↑0.17 ± 0.27°) compared to pre-testing (p < 0.05). Findings demonstrate significant BIA changes in muscles subjected to eccentric exercise, potentially aligned with evidence-based time courses of muscle recovery, which could inform monitoring strategies for training and rehabilitation. OpenScienceFramework Trial Registration ID: 8S2MN.