17b-Estradiol Induced Effects on Anterior Cruciate Ligament Laxity, Lower Extremity Biomechanics and Neuromuscular Activation Patterns in Females During Landing Activities

The purpose of this study is to expand on previous knowledge of the hormonal effects, specifically estrogen, on ligament laxity, motor control and timing of muscle activation in females. A significant amount of research has previously been done on the effects of estrogen throughout the menstrual cycle on ligament laxity with some showing a correlation of increased estrogen levels with increased ligament laxity. There have also been several studies that investigated muscle activation and ground reaction forces as related to hormone levels and stages of the menstrual cycle. A recent systematic review found a lack of research investigating muscle activation timing as related to hormonal changes despite theories suggesting muscle function including timing could be an explanation as to the potential causes for increased ACL injury correlated with the luteal phase of the menstrual cycle. The aim of this study is therefore to investigate whether hormonal changes throughout the menstrual cycle correlate with changes in ligament laxity, motor control, muscle activation and timing.

This study will be a longitudinal controlled study with two groups both containing females ages 18-35 years of age. The subjects will be placed into either the Experimental Group (no birth control) or the Control Group (on birth control) depending on the status of their contraceptive use. To ensure subject privacy, all investigators will be blinded to which group the subject is in during data collection except for the primary investigator who will do the initial meeting with the subjects to go through the informed consent, determine phase of menstrual cycle, and allocate the subject to a group based on their contraceptive use. From this point on, the subject will be identified by a subject number and all data intake and analysis will be done with the number identifier. Ovulation cycle will be identified by a self-administered ovulation kit, hormonal samples of Estrogen will be obtained by a saliva sample and sent to Salimetrics lab for analysis. Dependent measures will include recording subject single and double-leg jump off a 12- inch block and landing on a force plate to record muscle timing and ground reaction forces upon landing. Electromyography will be used to measure muscle activation timing of the quadriceps, hamstrings, gluteus maximus, gluteal medius, and gastrocnemius muscles. A 3-D measuring system will record trunk and hip flexion, femoral internal rotation angle, and knee flexion, extension and valgus angles. Finally, ligament laxity will be measured with a knee arthrometer (KT1000 or similar) device to record tibial anterior translation. Each subject will be tested, and each variable above will be recorded 2 separate times corresponding to 2 main phases in the menstrual cycle (Follicular and Ovulatory phases).