Date of Award

Spring 2000

Document Type



Life & Environmental Sciences

First Advisor

Jacqueline Brehe

Second Advisor

John Addis

Third Advisor

Mary Keefe


Recent studies of female athletes have shown that females are more prone to knee injuries than their male counterparts. This phenomenon has been attributed to several factors including anatomical structure differences such as quadriceps-hamstring imbalances, type of activity (specifically cutting and planting motions), use of braces, and hormonal differences. It is known that hormones like relaxin have an obvious effect on ligament composition, but the effects of other hormones on ligaments has yet to be fully determined. One particular study reported that a female is most susceptible to knee injuries during the pre-ovulatory phase of her cycle, when estrogen levels are peaking. This project was an attempt to show the effects of estradiol on ligament strength and stretch. The role of progesterone as a counter-effector of estrogen receptors was also considered. The original hypothesis was that increased levels of estradiol would decrease the weight limit the medial collateral ligament could withstand before breaking. A second hypothesis was that the breaking point of the ligament would not be affected, but the elevated levels of estradiol would increase the amount of stretch in the ligament prior to breaking. Peak human estradiol levels were simulated in prepubescent rats and mechanical tests on the ligament were performed to measure breaking point and stretch. Combined levels of estradiol and progesterone were also given and the mechanical tests were repeated. It was concluded that increased levels of estradiol did not affect the breaking point but did increase the amount of stretch in the ligament prior to breakage. Progesterone did inhibit the effects of estradiol.