Objective: To determine the effect of oral contraceptives (OC) on hamstring neuromechanics and lower extremity stiffness across the menstrual cycle (MC).
Design: Causal comparative.
Setting: Research laboratory.
Participants: Thirty, healthy, normally menstruating female volunteers who were using OC (OC group, n = 15) or not (non-OC group, n = 15).
Assessment of risk factors: Stiffness and hamstring neuromechanics were assessed at 2 points of the MC corresponding to low (menses) and high (ovulation) hormone concentrations. Menses testing took place 3 to 5 days after the onset of menses (or pills 3-5 for the OC group). Ovulation test session occurred 2 to 4 days after ovulation identified using a commercial ovulation kit (or pills 15-17 in the OC group).
Main outcome measures: Lower extremity stiffness and hamstring neuromechanics [stiffness, electromechanical delay, rate of force production (RFP), time to 50% peak force (T50%)] and blood plasma concentrations of estradiol-β-17, free testosterone, and progesterone.
Results: Estradiol-β-17, free testosterone, and progesterone increased at ovulation in the non-OC group and remained constant in the OC group. No changes were observed across the MC or between the groups in other variables (P > 0.05).
Conclusions: Although previous literature suggests a prophylactic effect of OC use with respect to musculoskeletal injury risk, our results indicate that OC use does not affect muscle properties in manners thought to reduce ACL injury risk.