DALLAS (December 4, 2001) - A new study commissioned by the National Athletic Trainers' Association Research and Education Foundation found that gender specific differences account for the high occurrence of ACL injuries in females. Results of the study were presented at the NATA Annual Meeting and Clinical Symposia in June and an abstract was recently published in the Journal of Athletic Training, the quarterly scientific publication of the National Athletic Trainers' Association. The study found that females are more prone to knee laxity and ACL graft failure after ligament reconstruction. This suggests that the type of hormone (testosterone in males vs. estrogen or progesterone in females) or the nature of exposure to it (sustained in males vs. cyclic in females) could affect the remodeling capabilities of the ACL and thereby alter the mechanical properties of the ligament. Therefore, female hormones produce episodic shifts in the balance of remodeling toward net tissue degradation, while no such shift occurs in males. The study was conducted at Texas Tech University Health Sciences Center by Stephen Fuzie, ATC, and James Slauterbeck, MD. "This is the first report correlating ACL injury to cycle day with confirmation of the actual hormonal level," said Fuzie. "It is our opinion that the clustering of injury early in the follicular phase of the menstrual cycle is a result of hormone changes within the ligament that occur following the rise of both progesterone and estrogen levels in the luteal phase." A key component to the hypothesis was to identify a period of time during the menstrual cycle where a disproportionate number of ACL injuries occur. Also, the study was designed to determine if ACL injury occurs randomly or is clustered around a specific phase of the menstrual cycle and to confirm the injury date and menstrual history by estrogen and progesterone measurements taken from saliva. A total of 37 female athletes - 25 college and 12 high school - were evaluated at the time of ACL injury over a three-year period. A questionnaire was filled out and a physical exam, MRI or surgery confirmed ACL injury. The correlations between saliva and serum estrogen and progesterone were 73 percent and 72 percent, respectively. Twenty-six of the 37 athletes injured their ACLs during the follicular phase of the menstrual cycle. Most ACL injuries occurred during the early part of the follicular phase of the cycle and decreased as the cycle progressed. The Foundation, affiliated with the National Athletic Trainers' Association (NATA), is dedicated to enhancing healthcare for the physically active through funding and support of research and education. NATA's 21,000-plus certified athletic trainers are experts in providing quality healthcare and applying the latest research and techniques in the evaluation, treatment and rehabilitation of injuries.