## 3 Results
### Muscle Activities  
#### 3.3.1 Muscle Activities for the Whole Motion Sequence  
The baseline (S0) average EMG curves of the participants (Figures 9 and 10) showed that, in both tasks, on the dominant side, DA and LD were activated at the beginning of arm lifting while FCU and BB were activated first at the beginning of the screw phase of the motion. In task T2, the non-dominant DA and LD had similar activity patterns to the dominant side, but with lower activity level. The same applied to LD in task T1. In comparison to the dominant DA, the non-dominant DA in T1 not only had a lower activity, but also a different pattern: the dominant DA curve climbed from arm lifting to screw while the non-dominant DA curve declined. During the screw phase of task T1, on the non-dominant side, an increase was observed in the FCU curve, but not in the BB curve. In the screw phase of task T2, both non-dominant FCU and BB had increased EMG activity, but less than the increase in the dominant ones. By comparing the baseline (S0) EMG curves between the two tasks, the FCU and BB on the dominant side and the BB, DA, and LD on the non-dominant side suggested higher activities in task T2 than in T1, especially during the screw phase. Overall, DA was the most active muscle and LD had the lowest activity in both tasks on both sides. The arm lifting phase was dominant in T1 with 33% of the motion and the screw phase with 19%, while the screw phase took the most time of the motion in T2 with 42% and the arm lifting phase with 20%. It was worth noting that, in both tasks, the arm lowering phase started simultaneously at the end of the screw phase. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{2}{c}{**Mean Value [CR10]**} \\ \hline  & Support level & Task overall & Dom. shoulder \\ \hline  & S0: no exoskeleton & 4.4 & 6.0 \\ \cline{2-3}  & S50: 50\% support & 4.6 & 5.7 \\ \cline{2-3}  & S100: 100\% support & 3.2 & 4.3 \\ \cline{2-3}  & S0: no exoskeleton & 5.8 & 6.3 \\ \cline{2-3}  & S50: 50\% support & 4.4 & 5.0 \\ \cline{2-3}  & S100: 100\% support & 4.2 & 4.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Borg ratings [CR10] of perceived exertion on tasks T1 and T2. The perceived exertion for tasks T1 and T2 was rated lower with increasing support force. Figure 10: The participants’ average EMG curves during the complete motion sequence, in task T2, under three test conditions. The shadows represent the standard deviations. Three motion phases are marked from left to right on the graphic: (1) arm lifting was between two red dashed lines; (2) screw was between two black dashed lines; (3) arm lowering was between two blue dashed lines. Figure 9: The participants’ average EMG curves during the complete motion sequence, in task T1, under three test conditions. The shadows represent the standard deviations. Three motion phases are marked from left to right on the graphic: (1) arm lifting was between two red dashed lines; (2) screw was between two black dashed lines; (3) arm lowering was between two blue dashed lines. Comparing the average EMG curves of the participants between the three conditions, a lower EMG level was observed in dominant DA and LD during 50-100% of the motion in T1 only in condition S100 and 30-100% in T2 in both condition sS50 and S100. The average EMG curves of non-dominant DA suggested a lower activity under the two supported conditions during 75-100% of the motion in T1 and 25-100% in T2. During the screw phase, the non-dominant LD had a lower EMG level only in S100 in T1 and on both supported conditions in T2. It should be noted that there was an obvious increase in EMG of the non-dominant LD in condition S100 in the arm lowering phase of both tasks. During the screw phase of task T1, the average EMG curves of dominant FCU and BB on S50 were over their baseline curves (S0). The dominant BB had a lower EMG level in both supported conditions during the screw phase of T2.