# Analysis of Surface EMG Parameters in the Overhead Deep Squat Performance
## 4 Discussion
These results are consistent with the findings of [PERSON] et al. [13; 41], who stated that there are no significant differences in muscle activation between the biceps femoris and two quadriceps muscles, vastus medialis and vastus lateralis, at various depths of squat in weightlifters. The \(MDF\) parameter confirmed thestatistically significant differences between RF and GM and also between RF and BF. The effect size for both %MVC and \(MDF\) in this group is large (Tables 7 and 8). In the analysis of co-activation between the rectus femoris and biceps femoris, as well as between the vastus medialis and biceps femoris, a clear upward trend (Table 9) in \(CA1\) values was observed with the improvement of the exercise technique. In line with [42], the squat does not compromise knee stability and can enhance stability if performed correctly. Similar co-activation results were also reported during the pre-squatting phase by [PERSON] et al. [43] to keep the knee joint torque stable and into slight flexion. The highest \(CA1\) values in group 3 indicate a better balance of activation between the knee extensors and flexors, which may indicate more effective motor control and knee stabilization. The co-activation of antagonist muscles is a protective mechanism that increases joint stiffness and protects it from uncontrolled movements [44]. In line with our study, the gluteus muscle plays a vital role in the link between the degree of correctness of deep squat performance and muscle excitation of the lower part of the body. [PERSON] et al. in [45] also report \"that presented systematic review supports the evidence indicating gluteus medius activity showing moderate to strong relationship with weight-bearing activities like squatting with patellofemoral pain syndrome\". The lower activity of the gluteus muscle in group 3 is not an abnormality but the result of a more economical and integrated movement pattern. According to [PERSON] et al. [11; 45], the gluteus medius works as a stabilizer of the femur and pelvis during weight-bearing activities. It may indicate that individuals in this group use more effective stabilization mechanisms. If the deep squat is performed correctly, the activation of the gluteus muscle is small in relation to the rectus femoris and the vastus medialis. [PERSON] et al. in [19] also notice that increased squat depth using relative loads may not increase gluteal activation and changes in squat performance may alter muscle involvement. Along with the deteriorating quality of the deep squat performance, statistically significant differences in excitation appeared between other pairs of muscles. In group 2, along with the decrease in the quality performance of the exercise, a statistically significant difference occurs in the excitation of RF and BF and of VM and BF, which can indicate that the activation of the biceps femoris could compensate for the lack of correctness of exercise performance. In group 1, where the exercise was performed the worst, no significant difference can be pointed out in the excitation of RF and GM and of VM and GM, which was the characteristic feature of group 3 with the best-performed deep squat. However, a statistically significant difference is still preserved between the excitation of RF and BF and of VM BF, which was characteristic of group 2. Our observations are consistent with the findings of [PERSON] et al. [19], who also reported that poorly performed squats are related to altered gluteal activation, indicating that the changes in squat performance may change muscle involvement. The appearance of statistically significant differences of RF and BF and of VM and BF in groups 1 and 2 can be related to less correctly performed exercise. [PERSON] et al. [41], in their studies, stated the hypothesis that the increased hip extension necessary to return from a deeper parallel squat will significantly increase biceps femoris activity compared to a shallow partial squat, but they proved something directly opposite.