title: The effect of menstrual-cycle phase on hamstring extensibility and muscle stiffness.
abstract: BACKGROUND
  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.
  
  
  METHODS
  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.
  
  
  METHODS
  8 women with normal menstrual cycles.
  
  
  METHODS
  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.
authors.affiliation: Dept of Exercise and Sport Science, University of North Carolina at Chapel Hill, USA.
authors.forename: David R
authors.initials: DR
authors.lastname: Bell
authors.forename: Megan P
authors.initials: MP
authors.lastname: Myrick
authors.forename: J Troy
authors.initials: JT
authors.lastname: Blackburn
authors.forename: Sandra J
authors.initials: SJ
authors.lastname: Shultz
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Guskiewicz
authors.forename: Darin A
authors.initials: DA
authors.lastname: Padua
mesh_terms: D000704:Analysis of Variance; D000070598:Anterior Cruciate Ligament Injuries; D016001:Confidence Intervals; D004576:Electromyography; D005260:Female; D006801:Humans; D007718:Knee Injuries / Q000517:prevention & control; D008597:Menstrual Cycle / Q000502:physiology*; D009043:Motor Activity; D018482:Muscle, Skeletal / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology*; D013177:Sports / Q000502:physiology; D013223:Statistics as Topic; D013848:Thigh / Q000502:physiology*; D013997:Time Factors