## 4 Discussion  
The main finding of this study was the fact that the 5-week pre-operative progressive exercise rehabilitation program with weekly monitoring contributed to a significantly lower muscle activity imbalance in the treatment group, both before and immediately after ACLR, as well as during the next 5 weeks in comparison to the control group. Moreover, the results showed that the Q muscle activity imbalance was significantly higher in comparison with H and G for both groups. Moreover, in the case of Q, although 5 weeks of pre-operative and post-operative rehabilitation was sufficient to regain the imbalance noted in the last week prior to surgery, it was still not satisfactory. Conversely, in H and G, the muscle activity imbalance was still significantly higher than that prior to ACLR, but reached a satisfactory level at the end of the rehabilitation program. These results provide valuable information for physiotherapists and physicians concerning the course of the rehabilitation process after ACLR, and indicate the need for rehabilitation immediately after an injury until the planned surgery is carried out and its subsequent continuation. First of all, the 5-week pre-operative rehabilitation program contributed to significantly less muscle imbalance each week after ACLR compared to the control group. Secondly, in the post-operative phase there was a trend of faster imbalance reduction in the treatment group than the control group. Thirdly, the greatest imbalance in muscle activity among the measured muscle was found in Q, so this muscle group may need special attention throughout the rehabilitation process. Lastly, despite the fact that 5-weeks of post-operative rehabilitation successfully restored Q muscle activity imbalance to a similar value as that of the last week before surgery, it still amounted to approximately 35%. An asymmetry above 20% (side to side) is implicated in abnormal movement patterns and asymmetrical limb loading strategies following ACLR which may indicate a high risk of ACL reinjury [29; 30; 31]. Thus, it is imperative that patients continue the rehabilitation process with addition work aimed at improving Q function. On the other hand, in the case of G and H, despite the fact that it was not possible to obtain the same degree of imbalance as before the surgery, it seems that a satisfactory value was achieved. In summary, it can beconcluded, that the use of sEMG in enables the monitoring of rehabilitation and its course, providing valuable feedback that can be used to individualize the entire process and inform decision-making to optimize sports participation following ACLR. Currently, there is no clear consensus on rehabilitation in the early stages following an ACL injury and preparation for reconstruction. There is no recommendation for the selection of exercises and their exact volume and intensity. For example, in a study by [PERSON] et al. [10], the pre-operative rehabilitation was based on the principles outlined in the American College of Sports Medicine position stand for progression models for resistance training for healthy adults. Nevertheless, the authors demonstrated that the 5-week progressive program combined with resistance training, pyometric exercises, and general exercises for balance and stability with perturbation training significantly improved knee function. Moreover, [PERSON] et al. [32] showed a beneficial effect of 6-week gymn- and home-based pre-operative rehabilitation on the single-legged hop test, which was also maintained 12 weeks after ACLR. Our study confirms previous findings and provides evidence for a positive impact of pre-operative rehabilitation on post-operative outcomes. After the 5-week pre-operative rehabilitation program, the rehabilitation course after the ACLR was faster for each of the measured muscles compared to the control group (e.g., Q by 36% vs. 27%; treatment vs. control group; respectively). It seems that this result can be explained by the \"muscle memory\" phenomenon.