Author(s): BOUVIER, J., PRUDENT, M., STAUFFER, E., PINGON, M., GONDIN, J., MARTIN, C., FOURÉ, A., Institution: UNIVERSITE CLAUDE BERNARD LYON 1, Country: FRANCE, Abstract-ID: 752

INTRODUCTION:
17beta-estradiol (E2), progesterone (P4) and testosterone (T), whose concentrations differ according to sex, oral contraceptive (OC) use and menstrual cycle phase, may influence the severity of exercise-induced muscle damage (1). However, muscle damage is not uniformly distributed among the muscles activated during exercise (2). Shear wave elastography provides a muscle-specific evaluation of muscle damage through changes in mechanical properties. This study aimed to examine changes in those properties after eccentric exercise according to sex, OC use and menstrual cycle phase.
METHODS:
Ninety-one healthy females and twenty males participants performed an eccentric exercise of the knee flexors, during the early follicular (EF), late follicular (LF) or mid-luteal (ML) phase, or while using OC for females, and at an arbitrary time point for males. Serum E2, P4 and T concentrations, blood creatine kinase activity, isometric maximal voluntary contraction (iMVC) force of the knee flexors and shear wave speed (SWS) of the biceps femoris, semitendinosus and semimembranosus were assessed before (PRE), immediately after (POST), two days (D2) and seven days (D7) after the exercise. SWS was measured during isometric contractions performed at 50% of the session-specific iMVC and at 50% of the PRE-iMVC (to standardize absolute force level across sessions) as well as during passive stretches to end-range of motion.
RESULTS:
In eumenorrheic females, E2 and P4 levels followed the typical menstrual cycle pattern, with lower levels observed in OC users and males (p < 0.001). T concentration was higher in males (p < 0.001). Creatine kinase activity increased similarly in all groups (p < 0.001). iMVC force decreased and partially recovered between POST and D7 in all groups but ML (p < 0.001). At 50% of the session-specific iMVC, changes in semitendinosus SWS mirrored the loss of iMVC force (p < 0.05). Conversely, at 50% of PRE iMVC force, semitendinosus SWS decreased from PRE and POST to D2 only in ML (p < 0.05). Resting semitendinosus SWS increased at D2 for all groups but returned to baseline by D7 only for LF and ML (p < 0.01).
CONCLUSION:
Active muscle mechanical properties and neuromuscular function were more impaired in the ML group when E2 levels decreased, which may partly reflect the beneficial role of E2 on muscle regeneration (1). In contrast, alterations in passive semitendinosus SWS resolved by D7 only in the groups with the highest E2 levels, consistent with a potential effect of E2 on connective tissue (3). Interestingly, higher T levels in males did not appear to alleviate the force loss related to exercise-induced muscle damage and the higher ethinylestradiol concentration in the OC group did not result in different mechanical or functional behavior compared with the EF group.

1) Jomard C., Gondin J. (2023). Physiol Rep, 11(19):e15798.
2) Goreau V. et al. (2022). Scand J Med Sci Sports, 32(9):1335-1345.
3) Fede C. et al. (2019). Plos One, 14(9):e0223195.