The Effect of Menstrual-Cycle Phase on Hamstring Extensibility and Muscle Stiffness

CONTEXT: Preventing noncontact ACL injuries has been a major focus of athletic trainers and researchers. One factor that may influence female noncontact ACL injury is the fluctuating concentrations of hormones in the body. OBJECTIVE: To determine whether muscle properties change across the menstrual cycle. DESIGN: Repeated measures. Testing was performed within 3 d after the onset of menses and ovulation. Repeated-measures ANOVAs were used to determine changes in variables across the menstrual cycle, and Pearson correlations were used to determine relationships between variables. PARTICIPANTS: 8 women with normal menstrual cycles. MAIN OUTCOME MEASURES: Active hamstring stiffness and hamstring extensibility. RESULTS: Hamstring extensibility (P = .003) increased at the ovulation testing session but hamstring muscle stiffness (P = .66) did not. CONCLUSIONS: The results indicate that hamstring muscle stiffness did not change across the menstrual cycle and hamstring extensibility increased at ovulation, when estrogen concentration increases.