Discussion

The aims of this study were to (1) investigate changes in kinematic outputs during resistance training across different phases of the menstrual cycle, and (2) assess whether symptoms and perceptions of motivation and readiness are associated with changes in kinematic outputs across two mesocycles in resistance trained females. 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. However, across all menstrual cycle phases, differences between expected compared to observed average peak mean velocity were of a trivial to small magnitude (~ 0.01–0.02 m·s−1) and within the accepted magnitudes of technological and biological error [22, 32, 33]. Both motivation to train and readiness to perform showed significant positive associations with training performance. However, only motivation remained significantly positively associated with training performance when accounted for in the multivariate model. Symptom domain mean T-scores for pain, concentration, behavioral change, autonomic reactions, and water retention were highest in phase 1 compared with all other phases. Moreover, the pain domain was positively associated with bench press performance but negatively associated with deadlift performance. Furthermore, motivation to train appears to have an association with changes in kinematic output. Finally, it should be noted that there is a higher prevalence of symptoms observed in menstrual cycle in phase 1. Consequently, menstrual cycle phase appears to have little influence on resistance training performance, but practitioners may want to consider differences in symptomology and adopt an individualized approach when working with female individuals.

Menstrual cycle phase appears to have little tangible effect on training performance. Notably, in each phase of the menstrual cycle, the discrepancies between expected and observed average peak mean velocity were ~ 0.01–0.02 m·s−1. From a practical standpoint, these differences are modest and are unlikely to have a meaningful influence on physical adaptations. Previous research has shown that the demonstrable effects of proven interventions (e.g., augmented feedback) tend to be of a greater magnitude (> 0.05 m·s−1) [36] with relative average set mean concentric velocity improvements of > 8% [37]. Furthermore, the minor fluctuations in kinematic outputs observed in the current study support the minimal changes in kinematic outputs that occur across the menstrual cycle in physical performance testing in female athletes [43]. While fluctuations in estrogen and progesterone have been suggested to exert neuroexcitatory or inhibitory effects on neuromuscular function in eumenorrheic females [3], on a global functional level during everyday resistance training, these changes appear to be smaller than once thought. Overall, these findings can be used by practitioners to justify consistent and planned training across the menstrual cycle and support the inclusion of females in exercise science research.

Motivation to train (β = 0.0005, p = < 0.001) and readiness to perform (β = 0.0006, p = < 0.001) were both positively associated with training performance in the univariate analyses. However, after adjusting for multiple factors in the multivariate model, only motivation remained a significant independent predictor (β = 0.0004, p = 0.021), suggesting a 100-point change in motivation would improve velocity by ~ 0.04 m·s⁻1. Alternatively, readiness was no longer significant (p = 0.40). This contrasts the equivocal findings from Dam et al. [20], who had indicated conflicting results between tests of physical capacity and motivation. These differences may be due to the current study being conducted in real-world training conditions across two mesocycles. Furthermore, the significant association between motivation and performance (refer to Table 4) suggest that motivation to train may have a greater impact upon resistance training performance when compared to the effect of menstrual cycle phase. Consequently, practitioners may wish to have open discussions with female athletes about changes in perceived motivation and readiness and emphasize that motivation, specifically, likely plays a key role in resistance training performance.

 | Univariate modelβ ± 95% CI | Multivariate modelβ ± 95% CI
Motivation to train | 0.0005 ± 0.00025* | 0.0004 ± 0.00030*
Readiness to perform | 0.0006 ± 0.00025* | 0.0001 ± 0.00035

The results of this study show that, across most symptom domains, participants’ mean symptom scores were highest in phase 1 compared to phases 2–6 (refer to Table 5). Additionally, the most prevalent symptoms reported in phase 1 were fatigue (75%) cramps (uterine or pelvic) (60.7%), backache (50%), and difficulty concentrating (50%). These prevalence rates are lower than those reported in active females by McNulty et al. [44], who observed approximately 90% for fatigue, 85% for period cramps, and 60% for both lower back pain and poor concentration during phase 1 (i.e., days 1–5 of the menstrual cycle). The discrepancies may reflect differences in the symptom assessment scales used or individual variability in symptom experiences [6]. Although most symptom domain scores were highest in phase 1, not all symptom domains appeared to be associated with performance. Furthermore, different domains demonstrated divergent relationships with bench press and deadlift performance. For instance, pain was positively associated with improved bench press training performance but negatively associated with deadlift performance. This divergence in how symptom domains relate to bench press versus deadlift performance may be explained by exercise-specific factors. For example, the bench press is an upper-body, horizontal pressing movement, whereas the deadlift is a lower body, hip-dominant, axial-load lift that relies heavily on trunk stability [45]. This distinction may be particularly relevant, as pain localized to the lower back, pelvis, or abdomen are commonly reported at different phases of the menstrual cycle [44, 46] and may compromise perception of trunk stability and impair the bracing required for effective deadlift performance. Future research is warranted to further elucidate the exercise-specific differences in how symptom domains relate to training performance. Additionally, investigating the effects of symptom severity on motivation and readiness may be valuable, given that symptoms may influence an individual’s performance. Collectively, these findings highlight that symptom influences on training performance are task specific, vary across exercises, and may need to be considered by practitioners.

Symptom domain | Phase 1 | Phase 2 | Phase 3 | Phase 4 | Phase 5 | Phase 6
Pain | 56.6 ± 13.4 | 48.4 ± 8.7 | 48.8 ± 8.6 | 47.7 ± 6.7 | 48.0 ± 7.6 | 49.0 ± 9.3
Concentration | 53.3 ± 12.7 | 47.8 ± 5.7 | 49.7 ± 7.5 | 50.4 ± 10.3 | 49.8 ± 11.3 | 51.1 ± 11.7
Behavioral change | 54.4 ± 15.5 | 48.8 ± 6.7 | 48.8 ± 5.6 | 49.6 ± 7.2 | 49.7 ± 9.7 | 50.2 ± 9.7
Autonomic reactions | 53.8 ± 14.5 | 48.9 ± 8.5 | 47.9 ± 2.9 | 48.3 ± 5.6 | 50.7 ± 9.7 | 48.8 ± 6.9
Water retention | 54.0 ± 16.4 | 48.2 ± 7.2 | 50.2 ± 8.5 | 49.9 ± 10.5 | 48.7 ± 7.8 | 57.5 ± 15.7
Negative affect | 52.2 ± 12.0 | 48.9 ± 8.3 | 48.3 ± 6.8 | 49.3 ± 9.2 | 49.1 ± 8.4 | 48.4 ± 7.5
Arousal | 49.7 ± 10.0 | 49.0 ± 9.3 | 50.3 ± 10.3 | 50.1 ± 9.1 | 51.0 ± 10.8 | 50.1 ± 10.8
Control | 50.2 ± 8.0 | 50.1 ± 8.4 | 48.8 ± 3.8 | 49.9 ± 8.2 | 49.0 ± 6.1 | 49.0 ± 4.6

It should be noted that while this is the first study to investigate longitudinal resistance training performance in resistance trained females across two menstrual cycles using gold-standard hormonal verification, there are several limitations. First, resistance training performance was quantified using observed versus expected mean concentric velocities during training using a linear change in expected velocities across the training mesocycle (i.e., each training session was estimated to have a similar effect on any potential change in the LVP). While this helped account for the natural adaptations that occur in response to training over time, which is rarely considered in normal training blocks due to pre- and post-measures often only being recorded, the expected values calculated for each session may not precisely reflect true neuromuscular capacity at those specific timepoints. While unlikely, it is possible that a certain session or relative intensity may have had a disproportionate effect on training adaptations that could not be accounted for. Nevertheless, as seen in the modest differences when comparing observed versus expected values, it is likely that the approach used provided a good estimate of neuromuscular capacity across the training cycles. Second, only the fastest repetition from each set was used for analysis. Prior research has shown that the fastest repetition of a set remains relatively unaffected by fatigue across multiple sets of the same exercise and continues to provide an accurate estimate of the load–velocity relationship [47]. Furthermore, the fastest repetition of a set not only represents current neuromuscular capability, it also has been shown to be closely related to the number of repetitions that can be completed within a set (e.g., faster first repetitions have been associated with the ability to be able to complete more repetitions with a given load [48]). Nevertheless, future research should consider whether there are changes in the kinetic and kinematic outputs across entire sets, as this could provide a greater understanding of the external demands placed on the individual. Third, due to the real-world training conditions of the study and the participants starting each mesocycle on day 1 of their menstrual cycle, it is possible that the small reductions in performance observed during phase 1 were influenced by increased fatigue responses that occurred as a result of novel intensities and volumes. Greater perceptions of soreness and neuromuscular fatigue often occur at the start of a new training block, and caution is warranted when suggesting that changes in neuromuscular fatigue occur as a response to ovarian hormone concentrations or symptoms in phase 1. While randomization of starting phase was considered (e.g., assigning some participants to begin in the early luteal phase), maintaining a consistent entry phase reduced logistical burden and allowed for standardized exposure to the programmed training loads across the menstrual cycle phases. Finally, the resistance training program was aligned with each participant’s individual menstrual cycle. Although all cycles were within the regular range (i.e., 21–35 days), both longer and shorter cycles were present. As a result, to ensure all participants completed the same total training volume across the study, some participants experienced longer or shorter durations between sessions, and this may have influenced the dissipation of fatigue between sessions.