## 4 Discussion
Therefore, we hypothesized that the symmetry of the coordinated movements of the R-L lower limbs during the STS motion could be evaluated by the R-L vector line. The \(ME\) of the R-L vector line analysis results provides information that can be used to identify which motion (left or right) is dominant based on the sign of the value (positive or negative) and its magnitude. In a previous study analyzing the STS motion of patients with femoral neck fractures, it was reported that the angular displacement of the knee joint and the hip joint is greater in the nonaffected lower limb, where the peak joint moment values are greater [30]. Therefore, by observing the \(ME\), the lower limb that is the primary source of force used to perform the STS motion can be estimated, helping to interpret the visually complex information on elevation displacement. Previous studies have reported asymmetry in the STS motion in patients after a lower limb fracture or a stroke [4; 5; 7; 19; 20]. According to the R-L vector line and the sign of the \(ME\) value, two trends were observed in the rehabilitated patient group. The first is patients with increased use of one lower limb during STS movements (Figure 7, P-1 and P-3), where the R-L vector line was also drawn on the side indicated by the sign of the \(ME\) value. The second was a patient with alternating and irregular increases in R-L lower limb use (Figure 7, P-2 and P-4). In this case, it was difficult to determine whether the predominantly used lower limb was the right or left one only by observing the R-L vector line, but the direction of the predominantly used lower limb could be determined from the sign of the \(ME\) value. On the other hand, compared with the rehabilitation patients, the R-L vector line of the healthy participants passed near the symmetric reference line. In other words, the R-L lower limbsof the healthy participants showed the possibility of coordinated temporal and spatial movement. [PERSON] et al. reported that a robotic rehabilitation intervention for stroke patients improves the muscle synergy asymmetry between the affected and nonaffected lower limbs [31]. In the study by [PERSON] et al., the symmetry between R-L lower extremities was assessed by the correlation coefficient of muscle synergy, but it only provides information on the similarity of muscle synergy changes between R-L lower extremities, not explicit symmetry. Another weakness of R-L symmetry evaluation using only muscle synergy is that the number of synergies must be the same in the R-L lower limb as a condition for comparison, and the results of muscle synergy analysis vary depending on the number and types of muscles being investigated [32]. The R-L vector line proposed in this study will clearly demonstrate the symmetry of STS R-L lower limb movements when the R-L vector line, which plots STS movements, approaches the symmetry reference line through rehabilitation of the patient. In addition, since the EAs of the thigh and lower leg are used, the problem of differences in the measurement target affecting the analysis results can be avoided. This makes the determination of the effectiveness of the rehabilitation of R-L symmetry reliable and easy to perform. The \(MSE\), which excludes the positive and negative signs of the \(ME\) and calculates the magnitude of the error between the symmetric reference line and the R-L vector line as a numerical value, is the mean error value obtained by dividing this value by the measurement time of each participant. Previous studies have reported that hemiplegia and pain reorganize the cooperative structure of muscles differently from the healthy side [14; 33; 34]. The R-L asymmetry of the lower limb movement pattern during the STS motion in the rehabilitation patient group could be quantified by \(MSE\) values. In the present study, the number of participants in both groups was small (four in each) and there was no significant difference in the statistical test for the \(MSE\).