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.