Effects of Menstrual-Cycle Hormone Fluctuations on Musculotendinous Stiffness and Knee Joint Laxity

Abstract

Higher rates of anterior cruciate ligament (ACL) injury in females may be related to hormonal fluctuations altering the properties of soft tissue in and around the knee. The purpose of this study was to examine changes in lower limb musculotendinous stiffness (MTS) and knee laxity over the course of the menstrual cycle and investigate the interaction of warm-up on MTS. Ten female netball players aged 16–18 years who were not using oral contraceptives participated in this study. Venous blood samples, together with MTS and knee laxity data were collected each week over the 28-day menstrual-cycle. MTS was assessed prior to, and following a standardised warm-up. ACL and posterior cruciate ligament (PCL) laxity was determined at the beginning of each test session using a KT-2000ä knee arthrometer. Repeated measures ANO VA revealed significant (p<0.05) main effects of test-session and warm-up on MTS. MTS was found to significantly decrease by 4.2 % following the warm-up intervention indicating that low levels of activity can acutely alter the viscoelastic properties of muscle. MTS was significantly lower at Week 3 (ovulatory phase) in contrast to Week's 1 and 2 (8.7 % and 4.5 %, respectively). For knee laxity measures, repeated measures ANOVA revealed no significant (p<0.05) differences across the menstrual-cycle. A reduction in MTS will increase electromechanical delay (EMD); therefore, muscles will take longer to generate tension to counteract deleterious forces within the knee joint. In this respect, MTS is proposed to be a contributing factor for the higher incidence of ACL injury at ovulation.