## 4 Discussion
### Second Part of Approach for Assessment of Quality of Motion  
Analyzing the results obtained for the chosen motion ranges (Table S1), we revealed differences in the kinematic data of the RS as well as in the DMD patient under PMC. These results indicate that instead of achieving the same functional goal (moving the external weight 100 g/1000 g in the horizontal plane from the outside to the midline of the body), the passive manipulator changed the trajectory of movement. Moreover, the EMG analysis (Table S3) showed that in the chosen motion ranges, there are significant differences in the muscular activity under PMC in comparison with NC. However, the differences were not revealed in all muscles. We found that the movement pattern of the DMD patient is different in comparison to the movement of the RS (Table S2). However, there is a lack of statistically significant differences in some ranges: (1) in **motion1** under NC in COM\({}_{z}\), WJ\({}_{y}\), \(\Delta\)COM, and \(\Delta\)WJ results; (2) in **motion2** under NC in \(\Delta\)COM, WJ\({}_{y}\), and COM\({}_{y}\) results; (3) in **motion1** under PMC in \(\Delta\)COM, WJ\({}_{y}\), and \(\Delta\)WJ results; and (4) in **motion2** under PMC in \(\Delta\)WJ, WJ\({}_{x}\) and \(\Delta\)COM results. We suggest that these similarities may be induced by the configuration of the tested upper limb to perform each functional task in a horizontal plane. Based on the ANOVA Kruskal-Wallis results, we found that the RS and the DMD patient under NC used different muscle activities to perform each motion in nearly all of the tested ranges (Table S4). Analyzing the results under PMC, we defined that: (1) in case of the RS, the most similar muscular activity is observed in both motions in the EMG\({}_{1}\)-EMG\({}_{2}\)-EMG\({}_{3}\) set and in **motion1** in the EMG\({}_{1}\)-EMG\({}_{2}\)-EMG\({}_{4}\) set; (2) in case of the DMD patient, the most similar muscular activity is observed in **motion2** in the EMG\({}_{1}\)-EMG\({}_{3}\)-EMG\({}_{4}\) and EMG\({}_{2}\)-EMG\({}_{3}\)-EMG\({}_{4}\) sets. Regarding the repeatability on the basis of the motion shape in the five RS trials and the three DMD patient trials (Figure 3 and Figure S1), we found that only in case of the RS did the passive manipulator facilitate motion and provide a more repeatable trajectory with a small variability. These findings agree with the evidence given in [26; 30]. Comparing the shape of the motion of the RS and DMD patient under NC, we found no repeatability. Our findings are in contrast to the results of [27], which report a high similarity in shapes of the gestures performed by forearm and hand of the DMD patient and healthy subject. In the case of the DMD patient, we observed compensation motions performed by his trunk. This behavior is reported in the literature, e.g., an analysis of kinematics revealed that DMD patients use increased trunk lateral bending and/or flexion-extension while performing reaching tasks and ADL tasks [20,25]. Additionally, comparing the mean motion trajectories of the tested subjects under NC, we revealed very small motions of DMD displacements related to the upper-limb COM, shoulder joint, elbow joint, and wrist joint. This behavior was caused by the compensation of the hand joints and fingers (in this study we did not analyze the kinematic data of these segments). However, under PMC this DMD patient performed more motions in his shoulder joint with respect to those of the RS. It is worth noting that the DMD patient examined in our study had a score of 5 on the Brooke scale. This is the lowest Brooke score, which indicates very little mobility in the upper limb. Our findings agree with ones described in [29], which states that the decrease in the active range of motion of the limb leads to its long static positioning (immobilization). This results in the development of contractures in joints of the upper limbs and compensation motions.