Neuromuscular and biomechanical characteristics do not vary across the menstrual cycle

Research examining the menstrual cycle and its relationship to ACL injury has focused on determining the incidence of ACL injury during the different phases of the menstrual cycle and assessing the changes in neuromuscular and biomechanical characteristics between these phases. Conflicting results warrant further investigation to determine if neuromuscular and biomechanical characteristics respond in a similar pattern to the fluctuating estradiol and progesterone. The purpose of this study was to determine if changes in the levels of estradiol and progesterone significantly altered fine motor coordination, postural stability, knee strength, and knee joint kinematics and kinetics between the menses, post-ovulatory, and mid-luteal phases of the menstrual cycle. Ten healthy and physically active females (Age: 21.4 ± 1.4 years, Height: 1.67 ± 0.06 m, Mass: 59.9 ± 7.4 kg), who did not use oral contraceptives, were recruited from the local university population. Single-leg postural stability, fine motor coordination, knee strength, knee biomechanics, and serum estradiol and progesterone were assessed at the menses, post-ovulatory, and mid-luteal phases of the menstrual cycle. Levels of estradiol were significantly higher during the post-ovulatory (P = 0.016) and mid-luteal phases (P < 0.001) compared to the menses phase. Levels of progesterone were significantly lower during the menses (P < 0.001) and post-ovulatory phases (P < 0.001) compared to the mid-luteal phase. No significant differences existed between phases of the menstrual cycle for fine motor coordination (P = 0.474), postural stability (P = 0.707), hamstring - quadriceps strength ratio at 60°s^-1 (P = 0.748) or 180°s ^-1 (P = 0.789), knee flexion excursion (P = 0.6), knee valgus excursion (P = 0.899), peak proximal tibial anterior shear force (P = 0.797), flexion moment at peak proximal tibial anterior shear force (P = 0.698), or valgus moment at peak proximal tibial anterior shear force (P = 0.924). The results of the current study suggest neuromuscular and biomechanical characteristics are not influenced by estradiol and progesterone fluctuations. All neuromuscular and biomechanical characteristics remained invariable between testing sessions despite concentration changes in estradiol and progesterone.