Results

Participant Characteristics

Twenty-eight participants completed the study. The mean ± SD for age, height, and weight was 27.1 ± 5.2 years, 166.6 ± 5.7 cm, 68.6 ± 10.8 kg, respectively. All participants contributed two menstrual cycles each, totaling 56 cycles across the intervention period. Participants’ menstrual cycle characteristics are presented in Table 2.

Variable | Mean ± SD
Menarche (years) | 13 ± 1.6
Menstrual cycle length (days) | 29.1 ± 2.7
Menstrual cycle range (days) | 23–35
Ovulation (day) | 16.2 ± 2.8
Length of follicular phase (days) | 16.2 ± 2.8
Length of luteal phase (days) | 12.9 ± 2.2

Of the 28 participants that completed the study, 22 participants were classified as eumenorrheic and six participants were classified as naturally menstruating (Supplementary Material 2; see the electronic supplementary material). Among the naturally menstruating participants, five out of six did not demonstrate the expected hormonal profile [24], with estradiol concentrations higher during the ovulation phase than the mid-luteal phase. For the remaining participant, the expected hormonal profile could not be confirmed as a mid-luteal blood sample could not be obtained.

Serum Hormone Concentrations

Serum 17β-estradiol and progesterone concentrations were assessed in the early follicular, ovulatory, and mid-luteal phases. The data are shown in Table 3.

Variable | EFP | OP | MLP
17β-estradiol (pmol/L) | 118.2 ± 62.4 | 350.7 ± 324 | 364.7 ± 265.1
Progesterone (nmol/L) | 9.2 ± 4.7 | 17.2 ± 6.8 | 41.8 ± 9.8

Observed versus Expected Performance

Figure 2 shows the observed versus expected plus effect sizes ± 95% CI for average peak mean velocity for the bench press and deadlift. Significant differences in observed versus expected average peak mean velocity were found in the bench press during phases 1 and 5, and in the deadlift during phases 1 and 6. For both exercises, the observed average peak mean velocity was ~ 0.01–0.02 m∙s−1, with the direction of deviation (greater or lower than expected) varying across phases. For the bench press, p values were 0.011, 0.497, 0.848, 0.215, 0.005, and 0.384 for phases 1–6, respectively. For the deadlift, p values were 0.038, 0.928, 0.120, 0.384, 0.064, and 0.049 for phases 1–6, respectively.

Fig. 2: Observed versus expected mean concentric velocity in the bench press and deadlift exercises. The zero line represents the expected performance determined from the load–velocity profiles. Points present the estimated marginal means ± 95% confidence intervals (CIs). Additionally, effect sizes ± 95% CIs are displayed directly beneath each point, and stars indicate statistically significant differences from expected performance (p < 0.05). The green shaded area indicates performing better than expected (i.e., observed mean concentric velocity greater than expected mean concentric velocity), while the red shaded area indicates performing worse than expected (i.e., observed mean concentric velocity less than expected mean concentric velocity)

Motivation to Train and Readiness to Perform

The univariate linear mixed-effects models showed that both motivation to train (β = 0.0005, p < 0.001) and readiness to perform (β = 0.0006, p < 0.001) were positively associated with training performance. However, in the multivariate model that accounted for menstrual cycle phase, exercise type, readiness, and motivation as factors, only motivation (β = 0.0004, p = 0.021) remained a significant independent predictor of training performance.

Menstrual Cycle Symptoms

The MDQ symptom domain T-score data are presented in Table 5. Across phases, most symptom domain scores were close to 50, indicating that participants’ symptom scores were near the sample mean at each phase. Phase 1 showed the highest mean T-scores for the pain, concentration, behavioral change, autonomic reactions, negative affect, and control domains. In contrast, the mean T-score for the water retention domain was highest in phase 6. Additionally, phase 1 showed the highest overall prevalence of symptoms compared to all other phases. The most prevalent symptoms in phase 1 were fatigue (75.0%), cramps (uterine or pelvic) (60.7%), backache (50.0%), and difficulty concentrating (50.0%). Further detail on the frequency, prevalence, and intensity of individual symptoms is provided in Supplementary Material 5 (see the electronic supplementary material).

The pain domain (p = 0.018) was positively associated with bench press performance. Specifically, for every arbitrary unit increase in the pain domain, mean concentric velocity increased by 0.00065 m∙s−1. In contrast, pain was negatively associated with deadlift performance (p < 0.001), with mean concentric velocity decreasing by − 0.001 m∙s−1 per arbitrary unit increase in pain. It should be noted, there was no significant main effect for control, but there was a between-exercise difference (p < 0.03). No other symptom domains showed significant relationships with training performance in either exercise.