Author(s): HEINRICH, C., HERZOG, K., VENTH, L., HAPP, K., NIEDERER, D., BEHRINGER, M., Institution: GOETHE UNIVERSITY FRANKFURT, Country: GERMANY, Abstract-ID: 1306

INTRODUCTION:
The menstrual cycle is a possible modulator of muscle function and performance due to cyclic fluctuations of steroid hormones and the presence of their receptors in muscle tissue. This study aimed to investigate differences in skeletal muscle function across distinct menstrual cycle phases in an eumenorrheic population.
METHODS:
Repeated within-subjects measures were conducted in early follicular, ovulatory, and mid-luteal phases across three consecutive menstrual cycles. Cycles were tracked using a mobile application, and ovulation was determined by a urinary luteinizing hormone surge. Estradiol and progesterone concentrations were analyzed in saliva. Isokinetic concentric and eccentric peak torque, fatigue resistance, and contractility of m. rectus femoris were quantified; shear wave elastography was used to evaluate muscle stiffness as mechanical muscle characteristic.
RESULTS:
Thirty-two physically active females (mean age 27.13 years, ± 4.13 years, height 1.68 ± 0.06 meters, average training per week 6.98 ± 3.01 hours, cycle length 28.66 ± 3.54 days) were enrolled. N = 14 completed all measurements across three cycles. Isokinetic peak torque (F (2, 129) = 1.94, p = 0.15), eccentric peak torque (F (2, 140) = 1.27, p = 0.28), squat jump height (F (2, 151) = 0.03, p = 0.97), countermovement jump height (F (2, 149) = 0.44, p = 0.65), drop jump height (F (2, 148) = 0.75, p = 0.47), and fatigue resistance outcomes such as total work (F (2, 143) = 0.71 p = 0.49) and change scores of isokinetic peak torque during the fatigue protocol (F (2, 138) = 1.14, p = 0.32) did not differ significantly between menstrual cycle phases. Muscle stiffness in a relaxed (F (2, 154) = 0.26, p = 0.77) and contracted state (F (2, 154) = 1.53, p = 0.22) did not differ significantly between cycle phases. Training hours were negatively associated with concentric peak torque (β = - 3.54 ± 1.16, p = 0.005), eccentric peak torque (β = - 5.14 ± 2.07, p = 0.02), and total work (β = - 57.48 ± 20.68, p = 0.01).
CONCLUSION:
Skeletal muscle function does not differ significantly between early follicular, ovulatory, and mid-luteal phase in an eumenorrheic population. While mechanistic background implies that menstrual cycle-induced hormone fluctuations would modulate musculoskeletal tissue, the practical impact on muscle function appears to be limited