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

<jats:sec sec-type="context"><jats:title>Context:</jats:title><jats:p>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.</jats:p></jats:sec><jats:sec sec-type="objective"><jats:title>Objective:</jats:title><jats:p>To determine whether muscle properties change across the menstrual cycle.</jats:p></jats:sec><jats:sec sec-type="design"><jats:title>Design:</jats:title><jats:p>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.</jats:p></jats:sec><jats:sec sec-type="participants"><jats:title>Participants:</jats:title><jats:p>8 women with normal menstrual cycles.</jats:p></jats:sec><jats:sec sec-type="main outcome measures"><jats:title>Main Outcome Measures:</jats:title><jats:p>Active hamstring stiffness and hamstring extensibility.</jats:p></jats:sec><jats:sec sec-type="results"><jats:title>Results:</jats:title><jats:p>Hamstring extensibility (<jats:italic>P</jats:italic> = .003) increased at the ovulation testing session but hamstring muscle stiffness (<jats:italic>P</jats:italic> = .66) did not.</jats:p></jats:sec><jats:sec sec-type="conclusions"><jats:title>Conclusions:</jats:title><jats:p>The results indicate that hamstring muscle stiffness did not change across the menstrual cycle and hamstring extensibility increased at ovulation, when estrogen concentration increases.</jats:p></jats:sec>