Value-Added: Importance of Incorporating Menstrual Cycle Phases to Clarify Sex-Related Differences in Force Steadiness

AimThis study aimed to determine whether female elbow flexion force steadiness varies across the menses, follicular and luteal phases of the menstrual cycle. MethodsTo control for repeated testing effects unrelated to hormonal fluctuations across the menstrual cycle, a comparison group of males completed the same protocol over three equally spaced testing sessions to the females. Maximal voluntary contractions and force steadiness were assessed in the neutral and pronated forearm positions. Elbow flexion force tracking tasks were performed at 2.5, 5, 10, 25, 50 and 75% maximal voluntary contraction in both forearm positions, and force steadiness was quantified as the coefficient of variation of force. ResultsMales were stronger than females (p<0.001), and maximal voluntary contractions did not differ between menstrual phases (p>0.14) or between days in males (p>0.56) in both forearm positions. There was no difference in coefficient of variation of force across sessions for the males (p<0.36). The coefficient of variation of force for all submaximal forces was significantly greater during the luteal phase compared to menses (Neutral p=0.02; Pronated p<0.05) but not the follicular phase (Neutral p=0.71; Pronated p=0.10). The coefficient of variation of force during the luteal phase in females was higher than males in both positions (p<0.02). ConclusionThese findings support previous observations that females are less steady than males for isometric steady contractions; however, this study identifies luteal specific phase effects. This underscores the importance of accounting for menstrual cycle phase when conducting sex-related comparisons.