Do fluctuations in oestradiol and progesterone across the menstrual cycle affect mechanical stiffness in female athletes?

OBJECTIVES

This exploratory study investigated the effect of fluctuations in sex hormones, oestradiol and progesterone, during the menstrual cycle, on mechanical stiffness, in naturally menstruating females and hormonal contraceptive users.

DESIGN

Observational, within subjects.

METHODS

Participants were 24 female (18-29 years) National Rugby League Indigenous Women's Academy players. At three phases of the menstrual cycle (early-follicular, late-follicular and mid-luteal), venous blood samples (oestradiol and progesterone) were collected. To quantify mechanical stiffness (vertical, leg and hip, knee, and ankle joint) analogue and co-ordinate data were collected, whilst participants completed three drop jumps, landing on two force plates. Trajectory and analogue data were reconstructed, labelled, and filtered in Vicon Nexus software. A linear mixed model was used to determine if there were significant interactions between hormone concentrations and measures of mechanical stiffness.

RESULTS

Ankle joint stiffness was significantly positively associated with oestradiol and progesterone concentration (p = 0.006, p = 0.020, respectively). Knee joint stiffness and leg stiffness were positively associated with oestradiol concentration (p = 0.009, p = 0.006, respectively), but not progesterone concentration. Hip joint and vertical stiffness were not significantly associated with either hormone.

CONCLUSIONS

Female rugby league players have significantly higher ankle joint, knee joint and leg mechanical stiffness when oestradiol was highest, typically during Phase-2 of the menstrual cycle. It is possible that dynamic stiffness of the lower limb joints acts as a protective mechanism. Future research should confirm this relationship and examine interventions to address changes in athletes' mechanical stiffness across the menstrual cycle in order to enhance performance and injury prevention.