Abstract
It has been proposed that endogenous estrogens may protect skeletal muscle integrity and promote the repair and recovery process after acute muscle damage. The purpose of this study was to examine both biochemical and performance indices of exercise-induced muscle damage (EiMD) across menstrual cycle phases and compare oral contraceptive pill users (OCP) and eumenorrheic non-users (EUC). A total of 12 women (5 EUC; 7 OCP) underwent a prolonged eccentric running EiMD protocol and were evaluated for biochemical markers of skeletal muscle damage including creatine kinase (CK), C-reactive protein (hsCRP), and myoglobin (MgB) as well as performance markers including strength, range of motion (ROM), soreness perception, and swelling during early follicular (EF), late follicular (LF), and luteal (LU) phases. Measurements were taken pre- and post-exercise and at 24, 48, and 72 h post exercise. No differences were observed in ROM, swelling, or pain perception in response to EiMD across menstrual cycle phases. The EUC and OCP groups showed similar increases in CK, MgB, and soreness perception in response to EiMD across menstrual cycle phases. Strength recovery differed across menstrual cycle phases and between the EUC and OCP groups (p=0.011), being optimal in phases with higher endogenous estrogen levels (LF and LU). We conclude that endogenous estrogens produced during the natural menstrual cycle may support improved strength recovery, despite immediate increases in muscle cell damage, regardless of oral contraceptive pill use.