Despite a decreasing gender gap in exercise participation, there still remains a significant under-representation of women in biomechanics and rehabilitation research [1]. One reason for this disparity is the complexity of the hormone fluctuations as part of the menstrual cycle [2]. Our goal is to isolate the effects, if any, of estrogen – one of the hormones involved in the menstrual cycle – on the muscle performance of the soleus and in the lower leg. The following study aimed to validate our protocol for measuring Electromyography (EMG) signals to quantify muscle activation and exercise-induced fatigability. In this study, participants (N = 7) between ages 18 and 20 were invited to participate in two experimental trials in which Shimmer3 EMG Sensors were used to record muscle electrical activity. During each trial, the participants performed five, single-leg calf raise holds to measure the maximum voluntary contraction of the gastrocnemius. The maximum voluntary contraction of the soleus was ascertained using five, 3-second upward pushes on a seated calf raise machine. The average percent difference between the two trials for the maximum voluntary contraction was 13.8% + 7.9% for the gastrocnemius medialis and 16.9% + 10.0% for the soleus. Interestingly, the muscle activation was greater in the second trial for 6 out of the 7 participants. This finding may highlight that participants performed better the more familiar they were with the exercises. Therefore, this emphasizes the need for randomizing the phase of the menstrual cycle our participants begin their trials in.We plan to incorporate basal body temperature measurements, period tracking calendars, and ovulation sticks in future studies as a non-invasive metric for predicting each participant’s menstrual cycle phase. By measuring the muscle activation of the gastrocnemius and soleus in each phase of the menstrual cycle, we will assess the effects of the menstrual cycle on muscle fatigability in order to evaluate how injury risk may differ between men and women as a result.
[1] Bruinvels G, Burden RJ, McGregor AJ, Ackerman KE, Dooley M, Richards T, Pedlar C. “Sport, exercise and the menstrual cycle: where is the research?” British Journal of Sports Medicine 51: 487 – 488, 2017.
[2] McNulty KL, “The Effects of Menstrual Cycle Phase on Exercise Performance in Eumenorrheic Women: A Systematic Review and Meta-Analysis.” Sports medicine (Auckland, N.Z.) 50: 1813-1827, 2020.