ECSS Paris 2023: OP-BM10
INTRODUCTION: Oestrogen and progesterone, the primary female reproductive hormones, have neuroactive properties, with oestrogen eliciting excitatory and progesterone inhibitory influences [1]. However, their effects on neuromuscular function across the menstrual cycle (MC) remain unclear [2]. Muscle force production is mediated by motor unit (MU) recruitment and discharge rate, the effective regulation of which is key for movement control and injury prevention. Female athletes have a higher risk of non-contact anterior cruciate ligament (ACL) injuries compared to male counterparts, which may be a result of impaired neuromuscular function [3]. Despite evidence suggesting hormonal fluctuations may influence this, no study has examined motor control and MU activation in the vastus medialis (VM) and vastus lateralis (VL) across the MC. METHODS: Ten recreationally active, eumenorrheic females (age: 30 ± 8 years; BMI: 24 ± 2.8 kg/m²) tracked their MCs across a minimum of two consecutive cycles (mean length: 28 ± 3 days), with luteinising hormone surges detected after 14 ± 2 days. Blood samples were collected at the early follicular (EF), pre-ovulatory (Ov), and mid-luteal (ML) phases to measure 17ß-oestradiol and progesterone levels. Knee extensor maximum voluntary contraction (MVC) was recorded, motor control was assessed via isometric trapezoid contractions at 40% and 75% MVC, and via a sine wave task at 25% MVC with real-time visual feedback. A 64-channel high-density surface electromyography (HDsEMG) electrode recorded VM and VL activity at 40% MVC, with root mean square (RMS) EMG calculated as peak amplitude within a 50ms window, expressed as a percentage of max RMS EMG. One-way ANOVA and mixed-effects models were used (p < 0.05). RESULTS: 17ß-oestradiol and progesterone varied significantly across the MC (17ß-oestradiol: EF, 159 pg/ml; Ov, 200 pg/ml; ML, 208 pg/ml; p = 0.028; progesterone: EF, 11.96 ng/ml; Ov, 12.11 ng/ml; ML, 39.27 ng/ml; p = 0.036). However, no significant differences were found in knee extensor maximal strength (EF, 408 N; Ov, 395 N; ML, 419 N; p = 0.393) or normalised VM and VL RMS EMG (VM: EF, 58%; Ov, 49%; ML, 55%, p = 0.324; VL: EF, 54%; Ov, 60%; ML, 50%, p = 0.775). Neuromuscular control remained stable across MC phases, with no differences in force steadiness at 40% (p = 0.756) and 75% MVC (p = 0.895) or motor control during the sine wave task (correlation coefficient, p = 0.199; normalised AUC, p = 0.116). CONCLUSION: These findings suggest hormonal fluctuations across the MC have minimal influence on VM and VL activation, knee extensor neuromuscular function, and motor control. However, further research is needed to assess individual MU behaviour across different contraction intensities and dynamic tasks to better understand sex-related differences in non-contact ACL injury risk. [1] Smith and Woolley (2004) Cleve Clin J Med [2] Piasecki et al. (2023) Sports Med Open [3] Schmitz et al. (2022) J Athl Train
Read CV Elisa NédélecECSS Paris 2023: OP-BM10
INTRODUCTION: Neuromuscular function is impaired following an unaccustomed bout of eccentric exercise, however, through the repeated bout effect (RBE) the muscle is protected from damage following a subsequent bout of eccentric exercise. As a result of unaccustomed eccentric contractions, structural muscle damage occurs in both sexes, meanwhile, the inflammatory response may be mitigated in females due to protective effects of estradiol, thereby attenuating the secondary effects of muscle damage and potentially limiting the magnitude of the RBE. We investigated the relationship between menstrual cycle phase and oral contraceptive use on neuromuscular impairments following the first bout of exercise, and the magnitude of the RBE. METHODS: Fifteen female participants performed two bouts of 150 maximal eccentric voluntary contractions of the elbow flexors four weeks apart. Normally menstruating females participated during the late follicular phase (day 10-14) of their menstrual cycle, as determined through cycle tracking, when estradiol is near peak, and progesterone is lower. Oral contraceptive users were tested on their placebo pill days (lower estradiol). Neuromuscular function was assessed for Bout 1 before the eccentric protocol and then again 48 hours following, and this was repeated 4 weeks later for Bout 2. The magnitude of the RBE is calculated as the difference between maximal voluntary contractions in bout 1 48hr post-eccentric protocol and bout 2 48hr post-eccentric protocol. RESULTS: Eccentric exercise-induced muscle weakness and soreness did not differ between groups following Bout 1 (p>0.05), and the magnitude of the RBE (p<0.05) was similar between groups (p>0.05). CONCLUSION: Females in the late follicular phase (classified as high estradiol) and females on combined oral contraceptives (low estradiol) had similar impairments in neuromuscular function following the first bout of eccentric exercise, and a similar RBE.
Read CV Amelia RillingECSS Paris 2023: OP-BM10
INTRODUCTION: Equestrian sports are dominantly by women and require a highly specific posture. Performance in horse riding result from dynamic interactions between the rider and the horse, which may contribute to musculoskeletal injuries (MSIs), particularly in the spine. Vibrational forces play a key role in both performance and health, potentially exacerbating MSIs. Throughout the menstrual cycle, fluctuations in sex hormone levels primarily estradiol and progesterone are known to influence postural control. However, their specific impact on expert riders, particularly in relation to vibration exposure, has never been investigated. METHODS: Eight female riders (22 ± 3 years) with regular menstrual cycles were tested on an equestrian simulator during two phases of their menstrual cycle: the early follicular phase (CHF) and the luteal phase (CPG). Five Inertial Measurement Units (IMUs; Shimmers) were placed along the riders spine (7th cervical, 10th thoracic, 3rd lumbar), on the head, and on the simulator. Four variables were computed to assess postural control, including trunk orientation and angular variance. Vibration exposure was analyzed using the root mean square (RMS) of accelerations at the head and along the spine, as well as the total vibration dose at the lumbar level (ISO 2631). Wilcoxon tests were performed to compare the variables between the two menstrual phases. RESULTS: No significant differences in postural control were observed between menstrual cycle phases (p = NS). However, vibration exposure analysis revealed that the total lumbar vibration dose and the root mean square (RMS) acceleration at the cervical level were significantly lower in the CHF phase compared to the CPG phase (p < .05). CONCLUSION: This study suggests that hormonal status influences lumbar and cervical vibrations in expert riders during horseback riding, while postural control remains unaffected. Specifically, vibration attenuation was observed during the luteal phase, when progesterone levels are high. Although further research is needed to clarify the underlying mechanisms, these findings provide valuable insights into both performance optimization and rider health.
Read CV Agnès OLIVIERECSS Paris 2023: OP-BM10