The Influence of a Competitive Football Match on the Knee Flexion and Extension Rate of Force Development and Isometric Muscle Strength in Female Football Players  
[PERSON]  
1 Sports Research Centre, Department of Sport Sciences, Miguel Hernandez University of Elche, 03202 Elche, Spain; [EMAIL_ADDRESS] (A.M.-I. ); [EMAIL_ADDRESS] (J.L.L.E. )1 Sports Research Centre, Department of Sport Sciences, Miguel Hernandez University of Elche, 03202 Elche, Spain; [EMAIL_ADDRESS]  
from 0.1 to 0.2 injuries per 1000 h [2]. An ACL injury occurs when the ligament is subjected to an excessive load that exceeds its mechanical tolerance, resulting in structural failure and compromised knee stability [3]. Scientific data suggest that female athletes are two to three times more vulnerable to ACL injuries than male athletes [4; 5], possibly due to sex-related differences in biomechanics and neuromuscular control of the trunk and lower limbs during football-specific actions [6]. In female football players, the primary mechanism of ACL injury occurs without direct contact, typically during pressing or tackling movements [7; 8], which involve deceleration and cutting actions [9]. It is well established that ACL injuries have a multifactorial causation, resulting from the interaction of various intrinsic (i.e., anatomical, biomechanical, hormonal and neuromuscular control variables) and extrinsic (i.e., shoe-surface interaction, bracing and physical and visual perturbations) risk factors in football players [6; 10; 11; 12]. These risk factors can be categorised as modifiable (i.e., environmental conditions, pitch characteristics, type of football shoes, player's body mass index, neuromuscular control and fatigue) and non-modifiable (i.e., anatomical structure, genetics, sex and history of previous ACL injury) [6; 12; 13]. Within neuromuscular control variables, it has been suggested that excessive quadriceps strength combined with decreased hamstring co-contraction increases the shear force exerted on the anterior-posterior plane of the tibia when the knee is fully extended (around 30\({}^{\circ}\)), raising the possibility of suffering an ACL injury [14]. In this regard, the rapid stabilisation of the knee by mutual and balanced neuromuscular work of the quadriceps and hamstring muscles during sudden and fast movements could minimise the potential risk of ACL injury [15]. For this reason, assessing the relationship between the strength of the quadriceps and hamstring muscles in the range when the knee is fully extended is recommended to be employed as a criterion to decide the return to play after an ACL injury [16; 17]. Additionally, it has been proposed that the hamstring-to-quadriceps (H:Q) ratio of maximal strength variables has limited accuracy in predicting ACL injuries. This limitation may be due to factors such as the cut-off values and body position during testing, which do not accurately replicate the conditions under which ACL injuries occur [18]. Moreover, alternative H:Q ratios have been proposed, incorporating measures such as the rate of force development (RFD) instead of maximal strength. Additional calculations based on fatigue index, muscle size and muscle activation within each muscle group have also been suggested to improve the accuracy of ACL injury risk assessment [19]. Another intrinsic risk factor that may contribute to an increased likelihood of developing an ACL injury in football players is the acute neuromuscular fatigue developed with football practice [20; 21]. Previous studies have coincided in pointing out that a football match leads to decreased quadriceps and hamstring muscle strength in both male and female football players [22; 23]. Hence, two risk factors for ACL injury may concur as there are important changes in the H:Q ratio of force variables caused by the transitory fatigue induced by the match play.