# Influence of the Menstrual Cycle on Performance in CrossFit(r)
## 1 Introduction  
Research studies on sports performance have increased in recent years, but there is a gap as females represent only 34% of the athletes studied, with only 6% of total publications being conducted exclusively on females. Thus, they remain underrepresented within sport and exercise science research [1]. Furthermore, it has traditionally been assumed that physiological responses to training and exercise are similar in men and women, so the results obtained in men have been used to be extrapolated to women [2]. The non-inclusion of female athletes has been justified by the methodological challenges with studying their hormonal status, including the menstrual cycle (MC) [3]. However, there is an increasing interest in female training and the MC because of the potential for optimizing athletic performance through understanding hormonal fluctuations, managing menstrual symptoms, and strategically timing training to phases of the MC for better adaptation and recovery. The MC's average length is 28 \(\pm\) 2.4 days and maybe divided into four phases, which are regulated by hormonal changes in the following order: menstruation, follicular phase (FP), ovulation, and luteal phase (LP). The FP lasts 12-14 days and shows low levels of estrogen and progesterone, ovulation takes 1 day and is preceded by an estrogen surge, and the LP lasts 12-14 days and is characterized as displaying high levels of estrogen and progesterone [5]. In fact, hormones show changes in concentrations over the MC and can have different target organs for promoting different physiological end points [6]. During the MC, the fluctuations in hormone concentrations through the different phases could lead to differences in neuromuscular performance and strength or aerobic training adaptations [7,8]. For example, estrogen augments our glycogen storage capacity and free fatty acid availability as a fuel source, and this could lead to decreased carbohydrate use or glycogen sparing [9]. In addition, high estrogen levels can be associated with enhanced gluconeogenesis and a greater uptake of glucose into type I fibers [10]. Consequently, a greater oxidative capacity is associated with lower blood lactate levels and time to exhaustion [11]. On the other hand, progesterone increases our heart rate, ventilation, and body temperature, which could lead to thermoregulatory alterations, increasing the subjective perception of greater exertion and causing decreased athletic performance [12,13]. A recent review has reported that responses to physical training can be different throughout the MC as exercise performance might be reduced during the early FP compared to the LP, and this could lead to different adaptations [14]. Research suggests that for resistance training adaptations in muscle mass and strength, FP-based training could lead to greater outcomes compared to LP-based training. However, there is no strong evidence supporting this information, and more studies are needed [15]. In this sense, a review of this information indicates that the early FP is unfavorable for all strength classes and peak performance in isometric strength is seen in the late FP, whereas isokinetic strength peaks during ovulation. In addition, the same study explains that dynamic strength is optimal in the late FP [1,16]. One possible explanation for this is that the results reported by other studies where trained and untrained females showed different strength and power performance metrics over the course of the MC [17]. In addition, there is interindividual variability in the MC, with disturbances (e.g., amenorhea, irregular menstruation, pain, etc.) that could explain the differences in physical performance and perceptions [18,19]. While some female athletes feel a decrease in their physical capacity, performance, and rate of perceived exertion over the different phases of the MC, others do not have the same perception [20].