## 4 Discussion
According to that, the landing vGRF BM LSI in terms of single-leg vertical hops was falsely high in patients whose postoperative physiotherapy was directly supervised by the physiotherapist for less than six months after ACLR. After analyzing the results obtained in the present study, the question arises as to what could have been the cause of the observed disturbances between the limbs at the time of the vertical hop landing. Alterations in the landing limb symmetry observed in the patients with less than six months of postoperative physiotherapy supervision may indicate some compensatory mechanism for ACL-reconstructed limb protection. A long-term neuromuscular asymmetry seems to be one possible reason, as several studies observed neuromuscular deficits in the ACL-reconstructed limb compared to the contralateral limb and compared to the healthy controls, even after approximately one year and longer postoperatively during different multi-joint movement tasks evaluated using force plates and three-dimensional movement analysis systems [16; 17; 43; 44]. [PERSON] et al. (2010) noted that females on average two years after ACLR landed with greater force on the contralateral limb compared with the ACL-reconstructed one [16]. According to [PERSON] et al. (2011), the male patients also presented a deficit in the ACL-reconstructed knee after an average of two years postoperatively, because it had its energy generation over time partially substituted by the hip joint power on the ipsilateral side [17]. [PERSON] et al. (2012) observed that the ACL-reconstructed female patients at an average of four years postoperatively had greater peak hip- and knee-adduction angles, greater hip internal-rotation angles, and decreased peak knee-flexion angles compared with healthy females [29]. [PERSON] et al. (2014) noted different landing strategies in ACL-reconstructed patients compared to healthy control participants [45] using the landing error scoring system (LESS) as an assessment tool of the jump-landing mechanics. Some authors have probably accurately suggested that whenever there is a possibility for the nervous system to substitute the function of the ACL-reconstructed limb, the nervous system will do so [17]. That would be in line with the greater between-limb asymmetries during the double-leg tasks than during the single-leg ones in the present study. In addition, another question arises, namely, what the consequences of the altered between-limb symmetry during hop landing may be. Altered loadings of the knee joint may trigger the development of osteoarthritis and therefore influence quality of life [13; 28]. Some authors also suggest that altered movement strategies in ACL-reconstructed patients are partially responsible for the high second-injury rates in this population [45]. Additional research is needed to clarify the clinical and functional importance of the observed alternations in ACL-reconstructed patients. The small number of participants may be considered as a limitation of this study. The manual ligament laxity assessment is a possible limitation. It would have been better if the analysis had been performed with a three-dimensional motion analysis. Taking the well-known ACL-injury gender bias into account, there remains a need for additional research on between-limb symmetry during double-leg and single-leg vertical hop landing in female ACL-reconstructed patients. From a clinical point of view, it is possible to improve the between-limb asymmetry during the jumping task landings observed by other authors, and in one of the studied groups in the present study in physiotherapy supervised by a specialist, lasting at least six months postoperatively.