Author(s): BOUVIER, J., FOURÉ, A., MARTIN, C., Institution: UNIVERSITE CLAUDE BERNARD LYON 1, Country: FRANCE, Abstract-ID: 1228

INTRODUCTION:
The menstrual cycle (MC) has recently been shown to affect the risk of muscle injury (1). Muscle strain injuries are thought to appear following active muscle lengthening (2), which highly involves muscle passive mechanical properties as previously reported (3). The aim of this study was to determine the impact of the MC on the passive hamstring muscles rigidity assessed with ultrasound shear wave elastography (SWE).
METHODS:
Twenty-two eumenorrheic young active females attended three identical testing sessions during their early-follicular (EF), late-follicular (LF) and mid-luteal (ML) phases, confirmed by hormonal measurements. Knee was passively extended (2°/s) by an isokinetic dynamometer from 90° to 80% of the maximal joint range of motion (RoM), for a hip angle of 70° (hip and knee fully extended = 180°). Shear wave speed (SWS) was measured using SWE in the biceps femoris long head (BF), semitendinosus (ST) and semimembranosus (SM) during passive stretches. SWS and knee joint torque were assessed every 10% of each participant’s RoM and every 10° of absolute knee angle (from 90° to 80% ROM or 120° [i.e., maximal common knee angle for the entire experimental population]). Linear mixed models were used to investigate the effect of the MC phase on maximal knee RoM, knee joint torque and on each passive hamstring muscle SWS. Post-hoc analysis was conducted using Tukey HSD test when appropriate.
RESULTS:
Maximal knee RoM remained consistent along the MC (P=0.22). The knee joint torque expressed relatively to each participant’s RoM was greater during EF and LF phases than during ML phase (P<0.001), while it did not differ throughout the MC for absolute knee joint angles (P=0.43). The SWS expressed relatively to each participant’s RoM was greater during the ML phase than during EF and LF phases in the BF (P<0.01), while it was greater during the EF and LF phases than during the ML phase in the ST (P<0.01). On the opposite, the SWS expressed in absolute knee joint angles did not differ along the MC (P=0.27, 0.07 and 0.47 for BF, ST and SM, respectively).
CONCLUSION:
When rigidity was expressed in function of absolute knee angles, no difference was observed along the MC. However, for angles relative to individual RoM, BF rigidity was at its highest point during the ML phase, while the ST one was at its lowest. Interestingly, the risk of muscle injury has been shown to be greater in the ML phase and the BF is the most injured hamstring muscle (1,4). While muscle rigidity has been correlated to markers of exercise-induced muscle damage (5), the link between muscle injury occurence and a potential modulation of hamstring muscles rigidity by the MC has to be further assessed.

1) Barlow et al., Med Sci Sports Exerc, 2024; online ahead of print
2) Edouard P et al., Nat Rev Dis Primers, 2023; 9:56
3) Lacourpaille L et al., Acta Physiol, 2014; 211(1):135-46
4) Ekstrand J et al., Br J Sports Med, 2012; 46:112-17
5) Xu J et al., Eur J Sport Sci, 2019; 19:508-16