The menstrual cycle is characterized by variations in the concentrations of female sex hormonal steroids, which may influence skeletal muscle performance. However, the literature presents discrepancies regarding the impact of different phases of the menstrual cycle in muscle strength in women of reproductive age.

To analyze the isometric muscle strength of elbow flexors in healthy adult women during different phases of the menstrual cycle.

This prospective cross-sectional observational study included 30 women aged 18 to 37 years, all with regular menstrual cycles and no use of contraceptives for at least four months. Participants were assessed during three phases of the menstrual cycle: follicular, ovulatory, and luteal. Assessments in the follicular phase were conducted on the first or second day of menstruation; in the ovulatory phase, on day 14; and in the luteal phase, one to two days before menstruation. Isometric muscle strength was measured using a hand-held dynamometer, with three repetitions of five seconds each, interspersed with 30 seconds of rest. Assessments were conducted with participants in an upright position and their elbows flexed at 90°. Numerical variables were analyzed using mean and standard deviation. Normality was verified using the Shapiro-Wilk test, and inferential analysis was performed using repeated measures Analysis of Variance (ANOVA) to compare muscle strength across the different phases, considering a significance level of p > 0.05.

The study included 30 participants (22.3 ± 3.61 years; 64.1 ± 12.2 kg; 1.63 ± 0.05 m). For right elbow flexion, the mean strength values were: 12.9 ± 3.16 kgf in the follicular phase, 13.8 ± 3.25 kgf in the ovulatory phase, and 13.2 ± 2.31 kgf in the luteal phase. For the left arm, the mean values were: 12.9 ± 3.14 kgf in the follicular phase, 13.4 ± 3.51 kgf in the ovulatory phase, and 12.8 ± 2.69 kgf in the luteal phase. No statistically significant differences were observed between menstrual cycle phases (p = 0.309).

Hormonal fluctuations throughout the menstrual cycle did not show a significant influence on the isometric muscle strength of elbow flexors in healthy adult women.

The findings of this study contribute to the understanding of the relationship between the menstrual cycle and muscle performance, providing evidence that upper limb isometric strength may remain stable across menstrual phases in healthy women. Future studies with larger sample sizes and assessments of different muscle groups may complement these findings and further deepen the understanding of this topic.