Females have a much higher incidence of anterior cruciate ligament (ACL) injuries in sports compared to their male counterparts. Most previous studies have focused on the different ACL injury mechanics between males and females;​ few studies have examined why some females suffer ACL injures and others do not. Recently, studies have pointed to greater knee joint laxity (KJL) as a potential contributor to the higher rate of ACL injury ,among female athletes with some researchers reporting that hormones influence joint laxity throughout the menstrual cycle. However, the recent findings of a relationship between hormones and KJL have been contradictory. Furthermore, how changes in KJL during the menstrual cycle affect knee joint loading, which ultimately leads to ACL injury, has not been investigated. Therefore, the purpose of these studies were to investigate 1) whether hormonal fluctuations influence KJL and 2) whether altered KJL during the menstrual cycle influences knee joint loading during movement.

Increased KJL was observed during ovulation in most female subjects;​ however, subject variations corresponding to hormonal fluctuations were detected. When this subject variation was correlated with knee joint mechanics, changes in KJL were positively correlated with changes in knee internal rotation and adduction loads. The findings indicated that alterations in KJL lead to increases in knee joint loads in selected high risk movements.

We conclude that the relationship between the menstrual phase and knee joint loads cannot be simply generalized without knowing an individual's changes in KJL. The influence of hormones on KJL was subject-specific, possibly explaining why some female athletes are more prone to ACL injuries than others. In considering an individual's loading mechanism at the knee as a risk factore, subject variations in KJL should be considered rather than the phase of the cycle.