| In the general population, females are 1.5-4.6 times more likely to tear their ACL than males. Hormonal fluctuations during the menstrual cycle partially explain this elevated injury risk. Most of the previous research has focused on the influence of hormones on ligament in healthy females with no history of ACL injury. Information is limited regarding the influence of hormones on muscle and ligament in females with a history of ACL injury. The purpose of this investigation was to determine if biomechanical and neuromechanical factors change across the menstrual cycle in females with a history of unilateral ACL injury. Twenty-four participants were recruited to participate with twenty subjects (height=168.6+/-5.3cm, mass=66.2+/-9.1kg) completing the testing protocol. Participants were tested (1) 3-5 days after the onset of menses and (2) within 3 days following a positive ovulation test. Separate paired t-tests were performed with menstrual cycle phase as the within-subject factor (menses vs. ovulation) for variables of interest. Knee laxity ( P=0.03), hamstring musculotendinous stiffness (P=0.03), estradiol-beta-17 (P=0.009), and progesterone ( P=0.003) increased at ovulation. Hamstring strength, rate of force production, and free testosterone did not change across the menstrual cycle (P>0.05). During the jump landing at initial contact, the following changes occurred at ovulation: the tibia became externally rotated (P=0.01) and external knee valgus moment decreased ( P=0.006). During the absorption phase the following occurred at ovulation: the tibia became externally rotated (P=0.05), the femur became internally rotated (P=0.05), knee varus moment decreased (P=0.03), knee valgus moment decreased ( P=0.003), knee external rotation moment decreased (P=0.007), and peak vertical ground reaction force decreased (P=0.04). Females with a history of unilateral non-contact ACL injury demonstrated altered biomechanical and neuromechanical profiles across the menstrual cycle. Knee joint laxity, hamstring musculotendinous stiffness, and jump landing biomechanics appear highly sensitive to changes in hormones across the menstrual cycle in females with previous history of unilateral non-contact ACL injury. The influence of the observed changes on non-contact ACL injury risk requires further study. |
