PURPOSE: Mechanical stiffness, the active ability of a joint or body segment to resist deformation, is an important indicator of athletic performance. Although differences in mechanical stiffness have been reported between the sexes, no research has examined whether mechanical stiffness is influenced by changes in hormones associated with the menstrual cycle (MC). This study investigated the effect of fluctuations in endogenous sex hormones, estradiol and progesterone, during the MC, on mechanical stiffness during a drop jump landing task, in female athletes.
METHODS: Twenty-four female Tier 3 National Rugby League Indigenous Women’s Academy players, aged 18 – 29 years were recruited via invitation to participate in a five-week Female Athlete Research Camp at the Australian Institute of Sport (AIS). At three phases of the MC (Phase-1, 2 and 4) venous blood samples were collected and athletes underwent a succession of physical performance assessments. To quantify mechanical stiffness (vertical, leg, and joint stiffness of the hip, knee, and ankle) analogue and co-ordinate data were collected, while participants completed three drop jumps from a height of 30cm, landing on two force plates. Trajectory and analogue data were reconstructed, labelled, and filtered through Vicon Nexus Software. A linear mixed model was used to determine if there was a significant interaction between hormone concentration and measures of mechanical stiffness. Statistical analyses were performed in Jamovi (version 2.3.26.0, Sydney, Australia) and alpha value was set at p < 0.05.
RESULTS: Ankle joint stiffness was significantly associated with rising estradiol and progesterone concentration (p=0.006, p=0.020, respectively). There was also a significant increase in knee joint stiffness and leg stiffness as estradiol concentration rose (p=0.009, p=0.006, respectively), although progesterone levels did not significantly affect either measure. Hip joint and vertical stiffness were not significantly influenced by either hormone.
CONCLUSION: Findings show that female rugby players have significantly higher ankle joint, knee joint and leg mechanical stiffness when estradiol levels peak, which is typically during Phase-2 of the MC. There was also a positive association between rising progesterone level and ankle joint stiffness. This may have implications for training periodisation and injury prevention. Future research should examine the potential impact of interventions that address changes in mechanical stiffness across the MC in athletes, so that, if necessary, coaches and practitioners can implement customised training regimens to aid performance optimisation and injury prevention.
Disclosures: This study was co-funded by Australian Catholic University, Wu Tsai Human Performance Alliance and the AIS Female Performance and Health Initiative.
