Document Type : Review Paper
Authors
Department of Sport Rehabilitation and Health, Faculty of Sport Sciences and Health, Shahid Beheshti University, Tehran, Iran
10.22089/smj.2025.17288.1776
Abstract
Introduction:
Among joint injuries related to sports movements, knee injuries comprise approximately 19–20% of all cases, with ligament damage accounting for roughly 50% of knee injuries. Among the various structural components of the knee, the anterior cruciate ligament (ACL) is of particular importance due to its anatomical position within the joint, structural complexity, abundance of diverse neural receptors, and its high susceptibility to injury. Consequently, ACL injuries are considered serious and a major concern in sports medicine. The ACL is an intracapsular ligament that plays a critical stabilizing role in the knee joint. ACL injuries occur via both contact and non-contact mechanisms, with approximately 70% resulting from non-contact events. Epidemiological studies demonstrate that women are significantly more susceptible to ACL rupture compared to men, particularly during high-impact, dynamic movements such as landing, pivoting, and abrupt directional changes. The overall incidence rates are estimated at 1 in every 50 men and 1 in every 36 women per season, with a reported rate of 68.6 ACL injuries per 100,000 people annually in the general population. These injuries often entail prolonged rehabilitation, diminished athletic performance, and an increased risk of osteoarthritis later in life. An estimated 150,000 to 200,000 ACL reconstructions are performed yearly worldwide. Multiple factors underlie the variability in injury incidence, including anatomical, hormonal, biomechanical, and neuromuscular influences. In recent years, the role of the menstrual cycle and its associated hormonal fluctuations has gained considerable attention regarding ACL injury risk. The menstrual cycle involves cyclical changes in female sex hormones primarily estrogen and progesterone that affect muscular, skeletal, and neuromuscular attributes such as joint laxity, proprioception, muscle-tendon stiffness, and neuromuscular coordination. For instance, elevated estrogen levels have been shown to reduce collagen synthesis, thereby compromising ligament structural integrity. This has led to the hypothesis that certain phases of the menstrual cycle may increase susceptibility to non-contact ACL injuries in women. Given the critical relevance of this issue for designing injury prevention programs and optimizing training schedules for female athletes, this systematic review was conducted to examine the menstrual cycle's impact as a significant risk factor for neuromuscular injury and its biomechanical effects on the ACL during dynamic activities. The review aims to determine whether specific menstrual phases predispose women to increased ACL injury risk.
Methods:
Comprehensive searches were conducted across the Web of Science, PubMed, SPORTDiscus, Medline, and SID databases. Inclusion criteria were: (1) healthy female participants aged 18–40 years; (2) menstrual cycle phases verified by biochemical analysis; (3) assessment of biomechanical and/or neuromuscular surrogate markers indicative of ACL injury risk, evaluated during dynamic tasks such as jumping, landing, or cutting; and (4) measurements performed across two or more menstrual phases. Studies lacking hormonal verification of menstrual phases were excluded to ensure classification accuracy and reduce misclassification bias.
Results:
Out of 419 articles identified, only eight met the inclusion criteria. Among these, four studies reported no significant association between menstrual cycle phases and ACL injury risk. Two studies indicated that the mid-luteal phase may increase susceptibility to non-contact ACL injuries, whereas one found a decreased risk during this phase. Three investigations reported cyclical variations in joint laxity, with two linking knee laxity changes to alterations in joint loading. Further findings included increased anterior tibial translation, diminished hamstring activation, and greater knee valgus angles during particular menstrual phases, all of which may compromise dynamic knee stability and elevate ACL injury risk during high-load activities.
Discussion:
Current evidence is inconclusive regarding whether a specific menstrual cycle phase definitively elevates neuromuscular and biomechanical risk factors for non-contact ACL injury. Discrepancies between studies may reflect variations in sample size, hormonal assessment methods, movement tasks analyzed, and the neuromuscular and biomechanical parameters evaluated. Hormonal fluctuations represent one component of a complex, multifactorial injury risk profile, to be considered alongside other intrinsic and extrinsic factors. Therefore, definitive claims about increased ACL injury risk in specific menstrual phases cannot be made. Clinicians and coaches should adopt cautious approaches when evaluating physical readiness, implementing preventive programs, and conducting screening, avoiding reliance solely on menstrual calendars. This review highlights the necessity of precise menstrual phase identification and direct hormone level measurement for clarifying the relationship between hormonal fluctuations and ACL injury risk. The observed increases in knee laxity during phases such as ovulation or the luteal phase and their association with modified joint loading underscore the importance of integrating hormonal considerations in injury prevention training. Considering individual variability in hormonal and neuromuscular responses, injury prevention and training regimens should be tailored accordingly. In summary, while hormonal changes throughout the menstrual cycle may impact neuromuscular and biomechanical function, current data do not conclusively link these effects to increased ACL injury incidence. Future research employing rigorous designs, larger cohorts, and standardized methodologies is essential to elucidate these associations and enhance injury prevention strategies for female athletes.
Article Message
This systematic review emphasizes that precise identification of menstrual cycle phases alongside direct hormonal quantification is critical for accurately assessing ACL injury risk in female athletes. Evidence of increased knee joint laxity and altered loading patterns during specific menstrual phases highlights the importance of incorporating physiological fluctuations into preventive strategies. The substantial inter-individual variability in hormonal and neuromuscular responses supports the development of personalized, phase-specific training programs aimed at enhancing neuromuscular control, reducing joint stress, and mitigating ACL injury risk. Future research should systematically examine endocrine, biomechanical, and injury mechanisms interplay to establish evidence-based protocols that optimize performance while protecting musculoskeletal health in female athletes.
Ethical Considerations
This systematic review did not involve human or animal subjects, and thus no ethical approval was required.
Authors’ Contributions
All authors contributed equally to this manuscript's preparation.
Conflict of Interest
No conflicts of interest relevant to this article are declared by the authors.
Acknowledgments
We express our sincere gratitude to all contributors for their dedication, patience, and tireless efforts. We hope this study will meaningfully advance research in this field.
Keywords
Subjects
