Author(s): YAN, C., WANG, C. K., WANG, S. C., HE, C. S., Institution: NATIONAL CHUNG CHENG UNIVERSITY, Country: TAIWAN, Abstract-ID: 1576

INTRODUCTION:
Estrogen is believed to have antioxidant and anti-inflammatory properties that may reduce exercise-induced muscle damage (EIMD). During the menstrual cycle, estrogen and progesterone levels fluctuate significantly between the early follicular phase (EFP) and the mid-luteal phase (MLP), possibly regulating EIMD and promoting repair (1,2). However, current research on muscle strength and cell membrane integrity after muscle damage in women at different menstrual cycle phases is limited, and studies integrating bioelectrical impedance phase angles used to assess cell membrane integrity are scarce (3). Therefore, this study aimed to investigate changes in muscle strength recovery and bioelectrical impedance markers in adult women after eccentric exercise during the EFP and MLP.
METHODS:
Twenty-four healthy women aged 18 to 35 with regular exercise habits and menstrual cycles participated in this study. Following a counterbalanced design, each participant performed an isokinetic eccentric quadriceps exercise protocol (30°/s; 5 sets of 10 repetitions) during both the EFP (2–5 days) and the MLP (20–25 days). Maximum Voluntary Isometric Contraction (MVIC), Reactive Strength Index (RSI) for Counter Movement Jump, and bioelectrical impedance parameters including phase angle (PhA) and extracellular water to intracellular water ratio (ECW/ICW) were measured pre-exercise (Rest), post-exercise immediately (T0), 24 hours (T24), 48 hours(T48). A two-way mixed design ANOVA analysis was conducted to assess the interaction between menstrual phase and time, with significance level of α = 0.05.
RESULTS:
No significant phase × time interaction was observed, but significant main effects of phase and time were found (p < 0.05). Immediately post-exercise (T0), MVIC, RSI, and PhA decreased, whereas ECW/ICW increased compared with Rest (p < 0.05). At T24, RSI and PhA increased relative to T0, while MVIC remained significantly lower than Rest. At T48, MVIC further increased compared with T24, while ECW/ICW decreased relative to T0.
CONCLUSION:
Eccentric exercise induced transient muscle damage, with partial recovery evident after 24 hours. Menstrual phase affected MVIC and PhA, MLP demonstrated overall more favorable status. It is suggested that menstrual phase should be considered in muscle strength assessments or training scheduling in women.