title: Anterior cruciate ligament elasticity and force for flexion during the menstrual cycle.
abstract: BACKGROUND
  A high occurrence of knee injuries have been observed in women during the menstrual cycle (MC). As a result, numerous studies have been conducted regarding knee ligament elasticity during the MC. Some researchers believe that since estrogen receptor b exists in ligaments and tendons in the knee, estrogen may modulate towards a state of laxity. However, increased tissue temperature also observed during the MC can predispose ligament and tendon laxness. Therefore, the purpose of this study was to assess in women the relationship between Estradiol (E2) serum concentrations and tissue temperature during the MC and their combined effect on knee laxity.
  
  
  METHODS
  Ten non-athletic young healthy females, 18 to 30 years of age participated in the study. E2 serum concentrations, anterior cruciate ligament (ACL) elasticity, and force to flex the knee (FFK), knee flexion-extension hysteresis (KFEH) were assessed both at ambient temperature (22 °C) and after 38 °C warming. Testing was performed multiple times during the participant's MC, for one full MC.
  
  
  RESULTS
  ACL elasticity was significantly higher (P<0.01) and FFK and KFEH were significantly lower (p<0.05) during ovulation when E2 levels were highest. ACL elasticity was still higher during ovulation after warming to 38 °C. But, the effects of MC on FFK and KFEH were reduced by tissue warming.
  
  
  CONCLUSIONS
  ACL elasticity, FFK, and KFEH was affected not only by E2 but also tissue temperature. However, E2 had more impact on ACL elasticity while tissue temperature had more impact on FFK and KFEH at 38 °C warming.
authors.affiliation: Department of Physical Therapy, School of Allied Health Professions, Loma Linda University, Loma Linda, USA.
authors.forename: Haneul
authors.initials: H
authors.lastname: Lee
authors.forename: Jerrold S
authors.initials: JS
authors.lastname: Petrofsky
authors.forename: Noha
authors.initials: N
authors.lastname: Daher
authors.forename: Lee
authors.initials: L
authors.lastname: Berk
authors.forename: Michale
authors.initials: M
authors.lastname: Laymon
authors.forename: Iman Akef
authors.initials: IA
authors.lastname: Khowailed
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D016118:Anterior Cruciate Ligament / Q000502:physiology*; D001696:Biomechanical Phenomena / Q000502:physiology; D001831:Body Temperature; D004548:Elasticity / Q000502:physiology*; D004958:Estradiol / Q000097:blood*; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology*; D008597:Menstrual Cycle / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology*
chemical_list: D004958:Estradiol