(3) ISOMETRIC MID-THIGH PULL AND COUNTERMOVEMENT JUMP PERFORMANCE ACROSS THE MENSTRUAL CYCLE IN NCAA DIVISION I BEACH VOLLEYBALL PLAYERS

Purpose: This study aimed to explore strength and power changes over a seven-week off-season period and determine the influence of menstrual cycle phase on performance. Methods: Eighteen NCAA Division I beach volleyball athletes (age=20.7±1.3 years; height=177.4±4.0 cm; weight=72.3±6.3 kg) underwent seven weeks of performance testing during the fall off-season period. Isometric mid-thigh pulls (IMTPs) and countermovement jumps (CMJs) were assessed two days apart using a force plate (VALD Performance, Brisbane, Australia). After completing a progressive warm-up, athletes performed a maximal IMTP to assess peak isometric force production. For the CMJ assessment, athletes performed a standardized dynamic warm-up followed by two maximal CMJs with hands on hips to assess maximal jump height and peak power. Menstruation was self-reported to determine menstrual cycle phase. Menstrual cycle phases were categorized as menstrual (Phase 1), non-menstrual (Phase 2), early luteal (Phase 3), and late luteal (Phase 4). Linear mixed-effects models were used to determine differences between each week while accounting for menstrual cycle phase on each variable (α=0.05). Results: IMTP peak force production increased at weeks 3 (p < 0.01) and 7 (p < 0.01) compared to week 1. Moreover, IMTP peak force production was greater overall during the early luteal phase (Phase 3) (p < 0.01). Week 3 (p < 0.01), week 4 (p=0.01), and week 7 (p=0.01) interactions with Phase 3 were significant, indicating that IMTP changes over time were influenced by menstrual cycle phase. In contrast, there were no changes in maximal jump height or peak power over seven weeks even when accounting for menstrual cycle phase (p >0.05). Conclusions: IMTP peak isometric force production increased over the course of the training program and was also highest during the early luteal phase of the menstrual cycle while maximal jump height and peak power did not change throughout the off-season. Our findings suggest that strength can be influenced by menstrual cycle phase and that coaches and athletes may benefit from including this as a tracking variable, particularly when assessing strength performance. Future research should explore the physiological mechanisms underlying hormone-based strength fluctuations and the potential impact on performance across various athletic disciplines and phases of a training year. Practical Applications: Menstrual cycle phase did not influence peak power production or maximal jump height but did affect peak isometric force production in beach volleyball players. Integrating menstrual cycle phase tracking into training programs may provide context for interpretation of fluctuations in strength and overall performance as well as allow coaches to make more informed programming decisions. Importantly, data were collected during an off-season period in which training and other stressors were limited. It is conceivable that the observed effects of menstrual cycle phase would differ due to the impact of other influential variables that have been shown to impact performance and recovery while in-season, which should be explored in future research. Acknowledgements: This project was also made possible in part by Grant Number T32-GM081740 from NIH-NIGMS award to GFM. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the NIGMS or NIH.