(08) PERFORMANCE FATIGABILITY AND NEUROMUSCULAR RESPONSES DURING FATIGUING DEADLIFT EXERCISE THROUGHOUT THE MENSTRUAL CYCLE IN NATURALLY MENSTRUATING WOMEN

Hormonal fluctuations occur across the menstrual cycle and can be divided into 3 phases: menstruation, ovulation, and post-ovulation/luteal. Previous research suggests maximal strength is unaffected by menstrual cycle phase. However, little evidence is available on the impact of hormonal fluctuations during fatiguing, resistance-based exercise in naturally menstruating women. As coaches, understanding the impact hormonal fluctuations may have on resistance exercise performance could provide insight on exercise prescription and athlete performance expectations.

Purpose: To examine the absolute strength, performance fatigability, and neuromuscular responses during resistance exercise performed to failure at a high intensity (70% 1RM) in naturally menstruating women during different phases of the menstrual cycle.

Methods: 10 naturally menstruating women (age: 20±1 yrs; height: 167.5±5.8 cm; body mass: 71.1±12.2 kg; avg cycle length: 30±4 days) with confirmed ovulation (via urinary ovulation test kit) performed a one-repetition maximum (1RM) for the deadlift followed by repetitions to failure at 70% 1RM during the 3 phases of the menstrual cycle (menstruation, ovulation, mid-late luteal). The participants completed pre- and post- exercise maximal voluntary contractions (MVC) using a mid-thigh pull dynamometer to assess absolute strength (pre-exercise MVC) and performance fatigability (%Δ pre- to post-exercise MVC). Electromyographic amplitude (AMP) and mean power frequency (MPF) was measured from the right biceps femoris muscle during each visit and was normalized to the 1RM as a percent for analysis. One-way repeated measures ANOVAs were performed to examine differences across the 3 phases of the menstrual cycle for absolute strength, repetitions completed, and performance fatigability. Separate 3 (phase: menstruation (P1), ovulation (P2), mid-late luteal (P3)) x 2 (time: first 10% repetitions completed, last 10% repetitions completed) repeated measures ANOVAs were used to examine changes in EMG AMP and MPF across time.

Results: There were no significant one-way ANOVAs for absolute strength (P1: 131±18 kg, P2: 134±21 kg, P3: 130±19 kg, p=0.744), repetitions completed (P1: 14±2 reps, P2: 13±2 reps, P3: 13±2 reps, p=0.215), or performance fatigability (P1: 27±9%, P2: 25±16%, P3: 28±14%, p=0.870). There was no significant interaction for EMG AMP (F(2,18)=0.458, p=0.569, pη²=0.048) or main effect of phase (p=0.669). There was a main effect of time for EMG AMP (F(1,9)=34.061, p< 0.001, pη²=0.791) that indicated the final 10% of repetitions completed (110.4%±28.5%) was greater than the first 10% (85.9%±19.4%). For EMG MPF, there was no significant interaction (F(2,18)=0.578, p=0.571, pη²=0.060) or main effect of phase (p=0.217) or time (p=0.089).

Conclusion: Similar to previous research on maximal strength, menstrual cycle phase did not affect performance fatigability and neuromuscular responses during fatiguing exercise at higher intensities in naturally menstruating women.  PRACTICAL APPLICATION: When performing exercise at loads typically prescribed for strength and hypertrophy adaptations, the phase of menstrual cycle should not influence performance metrics, such as repetitions completed or neuromuscular responses. Therefore, coaches and practitioners should program resistance training based on the goals, experiences, and potential symptoms associated with the menstrual cycle of the athlete and clients, and not cycle phase.

Acknowledgements: None