## 4 Discussion  
The aim of this study was to evaluate differences in actEMG and force between female football players with previous ACL injury and healthy players in BF, ST, VM, VL, GMax, and Gm during a maximal voluntary isometric contraction. Additionally, the study aimed to determine if differences occur based on the laterality of the injured limb. In relation to BF, NI players develop a muscle functional pattern that involves a significantly higher value in average actEMG in the BF compared to ACL players during the maximal voluntary isometric contraction for NDL. In the comparison between limbs, the ACL_DL players obtained significantly higher values in peak actEMG in BF for NDL, the non-injured limb, compared with DL, the injured limb. In NI players, no significant difference was obtained between limbs in the biceps or in any other muscle. Therefore, ACL players demonstrated reduced actEMG in the BF muscle compared to NI players. This inhibition of BF actEMG was also evident in the injured limb compared to the non-injured limb in ACL players. Recent studies have demonstrated that altered motor unit activity occurs after ACL surgery due to muscle inhibition. This mechanism explains changes in EMG signal resulting from the inflammatory components of the joint post-surgery, which promote presynaptic reflex inhibition of muscles surrounding the knee [8, 19]. [PERSON] et al. have shown that ACL players exhibit reduced motor unit rate coding and recruitment size in Q and H muscles [21]. This mechanism, combined with women's lower H actEMG during pre-contact high-intensity actions and the use of the ST muscle as a graft in ACL surgery, contribute to greater dysfunction and muscle imbalances, particularly in women [27, 34, 35, 52]. In our study, ACL players showed lower average actEMG in BF compared to NI. Additionally, ACL_DL players exhibited lower peak actEMG in BF on the injured side compared to the non-injured side. These findings support the high risk of imbalance described in the literature by H inhibition in women and show that it could be higher in ACL players [27, 35]. This deficiency is associated with the Q dominance stabilization pattern observed in women [31, 53], which results in an imbalance favoring the Q in the H/Q ratio [26]. Q contraction generates anterior shear force, which is typically countered by the H. If the H fails, the ACL endures increased tensile stress, acting as the sole antagonist to anterior shear forces [35]. During high-intensity stabilization tasks, if the H are insufficiently activated or inhibited while the Q torque of force is maximal, inadequate co-contraction may fail to counteract the action of Q, increasing the risk of ACL rupture. In relation to peak torque of force, no differences were observed between groups, ACL and NI, nor in DL or NDL in any muscle. However, in the comparison between limbs, the ACL_NDL players showed a significantly higher peak torque of force in H for the DL, the non-injured limb, compared to NDL, the injured one. Few studies have explored the functional relationship between actEMG and force outcomes; however, previous limited research has indicated a linear relationship between both during maximal voluntary isometric contraction [54]. This relationship results from the need to increase motor unit firing rates to overcome constant resistance in isometric tests [21, 55]. Therefore, achieving maximum actEMG should be the physiological response. Consequently, higher actEMG correlates with greater peak torque of force production. In our study, there were no statistical differences in torque development in Hs between ACL and NI players. However, in ACL_NDL players, significantly higher values in peak torque of force development were obtained for DL, the non-injured limb. Moreover, as has been shown before, ACL players developed significantly less average actEMG in BF during maximal voluntary isometric contraction.