## 1 Introduction  
The professionalization of women's sports, especially football, considerably raised the demand for physical training in recent years [1, 2], leading to an increase in injuries [3, 4, 5]. Epidemiological data indicate that women have a two to four times higher risk of anterior cruciate ligament (ACL) tears than men [6]. This percentage can be increased up to eight times in female athletes [7, 8, 9]. Since ACL injuries have a considerable impact on quality of life and medical costs, it is relevant to determine the injury risk caused by the difference in knee laxity according to the phases of the menstrual cycle. For this reason, knowledge of the correlation between physiological variation in women during the menstrual cycle and the risk of injury should be a key issue in the 21 st century [10].  
The menstrual cycle is defined as a period designating \"physiological changes that occur in fertile women and other female primates for the purpose of sexual reproduction\" [11]. In women, the menstrual cycle has an average duration of 28 days. During this period, hormonal fluctuations are present and make it possible to differentiate four phases: pre-ovulatory, ovulatory, post-ovulatory and menstrual. These episodes are controlled by several hormones, ovarian and steroidal, which each have different actions. During the pre-ovulatory or follicular phase, there is an increase in estrogen and follicle-stimulating hormone (FSH) levels [12]. Ovulation, on the other hand, is caused by a spike in luteinizing-hormone (LH) in synergy with a spike in FSH, produced by an increase in estrogen. Successively, the post-ovulatory or luteal phase is characterized by an increase in the concentration of progesterone and inhibition of FSH and LH [13].  
The menstrual cycle can be regulated by taking exogenous hormones, for medical reasons or as a contraceptive method. For these reasons, the use of oral contraceptives (OC) is increasingly common among young women. To date, no consensus could be reached on the positive or negative effect of OC on the incidence of ACL injuries [14].  
Knee laxity is characterized by the anterior displacement of the tibia on the femur when a load is applied to the posterior surface of the tibia. The main stabilizer of the knee, limiting this movement, is the ACL [13]. During excessive anterior translations, this ligament is put under tension, and can therefore be subject to ruptures. Many studies have reported greater anterior laxity at the knee in women compared to men, which may lead to a greater risk of ACL injury [15; 16; 17], especially with the onset of puberty [18]. Therefore, hormonal fluctuations in women must be taken into consideration. Indeed, steroid hormones influence ligament metabolism, as demonstrated by [PERSON] et al. on the ACL [19]. The estrogens and progesterone exert an action on the synthesis of collagen, modifying the fibrobl property and therefore its mechanical resistance to tension. In fact, correlations between increased blood estrogen concentration and reduced collagen levels have been observed, due to a decrease in the number of fibroblasts in the ACL [20]. Studies show that a high level of estradiol is responsible for the decrease in fibroblast proliferation and therefore the synthesis of ligament collagen [19; 21; 22], which affects ligament resistance, increasing its elasticity and its vulnerability to injury. Looking at the composition of the ACL, [PERSON] et al. have identified receptors for relaxin, a hormone known for its elastic property in tissues [23]. These findings suggest an action of this hormone on ACL laxity, which is predominant in women [23].  
Previously, two systematic reviews have been conducted to determine the association between ACL tears, knee laxity and menstrual cycle [6; 24]. However, more recent data have been published since their research. Therefore, the objective of this systematic review is to update the scientific knowledge about the influence of the menstrual cycle and OC on knee laxity and ACL injuries.