The proposed research is an observational study designed to compare estrogen and progesterone serum levels with knee and ankle joint laxity, and muscle reaction time as a measure of neuromuscular function. Three groups of women athletes with differing estrogen and progesterone profiles (normal menstrual cycles, amenorrheic, and exogenous estrogen supplementation) and one control group (male collegiate athletes) will be used to compare differences in joint laxity and neuromuscular function. Blood levels of estrogen and progesterone will be measured at four time points across the menstrual cycle.

Joint laxity and muscle reaction time will also be measured at each of these points. The investigator hypothesizes that knee and ankle joint laxity and muscle reaction time will significantly increase with increasing estrogen and progesterone levels.