## 3 Results  
The anthropometric body segment weights and center of gravity locations in the anatomic positions were taken from [PERSON]'s book [20]. The anthropometric segment lengths of the human body, as a function of the human height, were taken from [PERSON]'s book [22]. The tool weight used during the tests was 1.6 kg and considered the same for the calculations. The moments around the shoulder joints for Task 1 and Task 2, calculated with Equations (1) and (2), were 13.26 Nm and 21.69 Nm, respectively, with a 179 cm height and 72 kg weight representing the mean height and weight values of the test participants. The deltoid muscle forces from Equations (4) and (5) were 1293 N and 2114 N for Task 1 and Task 2, respectively. The exoskeleton forces from Equations (6) and (7) were 23.42 N and 38.32 N and the exoskeleton moments from Equations (8) and (9) were 8.26 Nm and 13.52 Nm for Task 1 and Task 2, respectively. Finally, the rack forces were calculated as 550 N and 901 N, respectively, for Task 1 and Task 2. These rack forces directly apply to the compression spring. The spring was selected to provide the forces between these values. In practice, the user can pre-compress this to provide less or more force. The muscle activities for Task 1 and Task 2, defined in the previous section, are shown in Figures 9 and 10, respectively. The primary muscles doing the work for Task 1 were the AD and MD responsible for the shoulder flexion, the UT responsible for the elevation of the scapula, the MT and LT responsible for the scapular adductor (retractor), and the BB responsible for the elbow flexion. The other muscles were supportive in this task. Wearing the exoskeleton decreased the activity of the AD by 27%, the MD by 55%, and the PD by 37%. The other muscles were not much affected in comparison to the deltoid. However, the lower trapezius muscle activity was increased slightly, by around 4%, with the exoskeleton. For Task 2, the primary and supporting muscles were the same as those in Task 1, but all the muscles' activities increased. This was an anticipated result, because the tool was held further from the moment point of the shoulder in Task 2. The AD activity decreased by 38%, MD decreased by 48%, and PD decreased by 20% when wearing the exoskeleton. In addition, the UT and MT activity were also decreased by 37% and 27%, respectively. Since there was a greater moment around the shoulders for Task 2, the trapezius muscles actively participated in performing such posture. Unlike the UT and MT, the LT is located around the spinal cord and lower back. Therefore, the LT was also responsible for stabilizing the torso posture in Task 2. Consequently, the LT activity increased by 22% when the human arms were reached forth to help the torso stand still. This could be attributed to the \begin{table}
\begin{tabular}{c c} \hline \hline
**Specs** & **Value** \\ \hline EMG sampling rate & Up to 4000 Hz \\ EMG internal sampling resolution & 24-bit \\ EMG baseline noise & \textless{}1 \(\mu\)V \\ \hline \hline \end{tabular}
\end{table} 
Table 2: EMG device specifications. complicated dynamic motion of the scapula for shoulder-complex-related motions. The BB activity is slightly increased by 4% in Task 2. Muscle activity is considered to be a direct measure of muscle force. However, metabolic cost is not only related to the force generated in the muscles, but also to how fast they contract, and exoskeletons may alter the speed of these muscle contractions. When raising the upper arm, there is no resistance up to 120 degrees, because the arm rests are extremely light and connectors are attached to the wrist band with ball-and-socket joints, where no moment reactions occur. Therefore, no contraction velocity change and  
Figure 10: Comparing muscle activities without and with exoskeleton for Task 2. Figure 9: Comparing muscle activities without and with exoskeleton for Task 1.  
additional metabolic cost is expected for just wearing the exoskeleton when raising arm up to 120 degrees.