Fluctuations of semitendinosus muscle rigidity during the menstrual cycle.

OBJECTIVES

Exogenous 17β-oestradiol enhances the muscle fibre stiffness measured during contraction in rodents, but the potential impact of the endogenous variations in ovarian hormonal concentrations over the menstrual cycle in humans remains unclear. The aim of the present study was to determine whether the active mechanical properties of the hamstring muscles change throughout the menstrual cycle or with oral contraceptive use in females.

DESIGN

Cross-sectional study with repeated measures.

METHODS

Shear wave elastography measurements were conducted on contracted hamstring muscles during three distinct phases of the menstrual (N = 20) and oral contraceptive (N = 12) cycles. Serum hormonal concentrations (i.e., 17β-oestradiol and progesterone) and electromyographic activity were monitored alongside assessments of maximal voluntary contraction torque.

RESULTS

Maximal isometric voluntary torque remained consistent throughout both the menstrual and oral contraceptive cycles. In eumenorrheic females, the semitendinosus rigidity was greater in the early follicular phase than in the mid luteal phase (p = 0.004, +7.3 %), whereas this pattern was not observed in oral contraceptive users. This reduction in the semitendinosus rigidity during voluntary contraction was significantly correlated with the rise in progesterone concentrations between these phases (p = 0.001, r = -0.46).

CONCLUSIONS

Semitendinosus rigidity appears to vary throughout the menstrual cycle. The lack of such variation in oral contraceptive users, combined with the correlation with blood progesterone levels, suggests that this hormone may influence muscle rigidity during contraction. However, as the effect size was small and below the measurement variability, further studies are needed to confirm the specific effects of progesterone on muscle tissue.