Investigating the Sensitivity of Phase Angle to Eccentric Exercise of the Biceps Brachii: A Brief Report

Phase Angle (PhA), a measure of cellular health that is collected during bioelectrical impedance analysis (BIA), is sensitive to fluid shifts, which occur during high-intensity exercise, but its role in tracking these changes during muscular recovery is unclear. Therefore, the purpose of this study was twofold; the first objective was to investigate the sensitivity of PhA to muscular damage following an acute bout of eccentric exercise. The second objective was to investigate the potential use of PhA in tracking muscular recovery in the 72 hours following exercise. In this study, participants performed a maximal voluntary isometric contraction (MVIC) in both nondominant (EX) and dominant (CON) arms, then completed sets of 10 eccentric biceps curls at 45°•s^-1 using the EX arm. After each set, participants rested for one minute, then completed an MVIC in the EX arm to assess strength loss. This cycle continued until MVIC decreased by ≥60%. Pre-and post-exercise BIA scans measured segmental PhA and compartmental fluid in both arms. Subjective soreness and pressure-pain threshold (PPT) in the EX arm were recorded. Participants returned for three consecutive days for assessments of MVIC and BIA in both arms, and soreness and PPT in the EX arm. A 2×5 RMANOVA tested differences between EX and CON arms for impedance variables and MVIC. A 1×5 RMANOVA tested differences in PPT and visual analog scores (VAS). Significant differences were found in EX arm MVIC (p<0.001, ηp²= 0.109), extracellular water (p<0.001, ηp²= 0.003), intracellular water (p=0.001, Ƞ² _p= 0.005), and total body water (p=0.004, ηp²= 0.001). No significant differences were observed in EX arm PhA (p=0.784), PPT (p=0.079), or soreness (p=0.583). While exercise produced notable strength impairments (average percent change pre-to-post protocol: -35.24%) and fluid shifts, PhA and pain measures were unaffected. Thus, based on the results of the current study, PhA may not be sensitive to or related to classic indices of muscle damage.