Introduction

The menstrual cycle is a biological rhythm where fluctuations in endogenous sex hormones occur [1]. Specifically, estrogen and progesterone fluctuate in a cyclical pattern that can exert a range of physiological and psychological effects [1, 2]. For example, a neuroexcitatory effect within the central nervous system has been reported alongside elevated levels of estrogen, which may facilitate motor unit recruitment and influence force production [3]. Alternatively, progesterone has been proposed to exert inhibitory effects, which may influence motor unit firing rates and voluntary activation, and mitigate force generating capacity during exercise [3]. However, evidence is mixed regarding whether phase-dependent changes in hormone concentrations across the menstrual cycle can influence physical performance [1, 4–6]. The evidence objectively quantifying these performance changes is often tenuous and has been limited by poor methodological quality [1, 6]. Furthermore, studies that have investigated whether changes in physical performance occur across the menstrual cycle have often constrained their focus to singular testing timepoints and do not represent usual training conditions.

Menstrual cycle symptoms are commonly reported by female athletes [7]. Previous studies indicate that ~ 50–93% of female athletes perceive their menstrual cycle influences their ability to perform or train [8–10]. In addition, greater symptom frequency or severity has been associated with more negative performance perceptions during these symptomatic days [11, 12]. Recent research has demonstrated that menstrual cycle symptoms have a stronger association with changes in sleep and physiological outcomes than variations in endogenous sex hormones and should be considered as a viable pathway for altered exercise performance [13]. While evidence is scarce, it is plausible that common negative symptoms (e.g., fatigue, anxiety, cramps, poor sleep) inhibit performance and may hinder training if not managed appropriately. While it is important to acknowledge that there is substantial intraindividual variability in menstrual cycle-associated symptoms and how symptoms may influence training and performance, the majority of sports science research has failed to document the effects of these lived experiences on training outcomes.

Resistance training is a potent stimulus for developing strength, power, and hypertrophy [14]. It involves muscular exertion against an external mass and is strongly recommended by the American College of Sports Medicine as a form of exercise for females that has demonstrable effects on health, wellbeing, and longevity [15]. It has previously been posited that resistance training performance may be impacted by the menstrual cycle [16]. However, studies that have verified estradiol and progesterone concentrations have shown no significant correlation between menstrual cycle phase and physical performance [17–19]. Nevertheless, decrements in physical performance have been associated with negative menstrual cycle symptoms [19] and diminished perceptions of preparedness, such as reduced motivation and readiness to perform [20]. However, it should be noted that the studies by Smith et al. [19] and Dam et al. [20] assessed physical performance only at isolated timepoints (i.e., testing rather than training), which precludes the examination of day-to-day fluctuations in physical capacity across a mesocycle. Therefore, by monitoring resistance training and quantifying changes in kinematic outputs during exercise, practitioners can gain better insight into how physical performance can change according to menstrual cycle phase, perceived symptoms, motivation, and readiness.

Monitoring kinematic data during resistance training can be useful for the assessment of training performance and physical adaptation [21]. When undertaking resistance training, changes in velocity expression can be used to guide load prescription, assess fatigue, and quantify changes in training performance [21]. This is made possible due to the linear relationship between repetition velocity and external load (i.e., as a percentage of one-repetition maximum [1RM]) and the close relationship between fatigue and the unintentional decrease in exercise velocity. Therefore, it is possible to quantify changes in training performance across the menstrual cycle by monitoring the kinematic outputs that are produced within each training session. This approach to monitoring resistance training is not only commonly used within athletes across a range of demographics but is potentially one of the most ecologically valid methods of assessing whether changes in resistance training performance align with perceptions of decreased performance and fatigue [22, 23].

Considering the above, 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. It was hypothesized that menstrual cycle phase would not influence training performance but kinematic outputs would be negatively affected when there was a greater prevalence of symptoms.