# Validation of Cable-Driven Experimental Setup to Assess Movements Made with Elbow Joint Assistance
## 4 Discussion  
The range of motion exercises performed during rehabilitation that aim to restore the functional activities of daily living (ADLs) for stroke patients involves repetitive flexion and extension motion. ADLs can require a contribution from various joints to perform any motion. However, in this article, we focus on the elbow joint. It was found in other studies on the elbow joint that for multiple subjects, the elbow joint position was mostly under 90\({}^{\circ}\) during rehabilitation sessions with Armeo(r) Spring [41]. Additionally, we can observe that for active assisted elbow flexion-extension in the middle phase, there may be a requirement for a greater elbow angle than 90\({}^{\circ}\) towards extension [44]. In the case of bicep curls during rehabilitation/exercise, elbow flexion-extension ranges between 90\({}^{\circ}\) and 160\({}^{\circ}\)[45]. For the elbow, to restore motion after an olecranon fracture, the active flexion exercises are restricted from 80\({}^{\circ}\) to full extension initially [40]. In the case of a coronoid fracture, the extension is restricted between 120\({}^{\circ}\) and 140\({}^{\circ}\) for the duration of rehabilitation [40]. Also, all these rehabilitation exercises are repeated around 10 to 20 times per hour, which makes understanding cable-driven exosuit performance critical [40; 44] in the range of 80\({}^{\circ}\) to 140\({}^{\circ}\). If a cable-driven exosuit is used for assistance during rehabilitation, the optimal position of the anchor points can be chosen depending on the range of the intended task [19; 20]. From the presented results, if our aim is to optimize the performance of the cable-driven exosuit, then for the range of motion of exercise within 100\({}^{\circ}\), anchor point \(d_{1}\) can  
Figure 9: (**a**) Variation in optimal anchor positions, \(d_{1}\) and \(d_{2}\), with respect to the elbow joint angle in order to minimize cable tension and the reaction force at the elbow joint. (**b**) I-III depict the scenario of cable attached at different values of \(d_{1}\) and \(d_{2}\) for joint positions 55\({}^{\circ}\), 90\({}^{\circ}\), and 120\({}^{\circ}\). Green and red cables represent optimal and non-optimal positions. be attached closer to the elbow, and for exercises beyond 100\({}^{\circ}\), both anchor points \(d_{1}\) and \(d_{2}\) can be placed at the farthest point from the elbow. Further, if our aim is to optimize comfort, then the results suggest that both the anchor positions \(d_{1}\) and \(d_{2}\) should be farthest from the joint. These two scenarios depend on the time of the operation. For example, if the device is used on multiple subjects for short durations, the performance of the device can be prioritized over user comfort. If the device is used on a single subject over a longer duration, the comfort of the wearer should be prioritized. Current state-of-the-art studies on cable-driven elbow exoskeletons optimize the position of anchor points around the upper arm and forearm while keeping the distance from the elbow fixed [35; 36]. However, from the above results, it is evident that there is a significant change in the cable tension with the position of the anchor points from the elbow along the joint position. Figure 8a shows that the effective position varies by a significant margin for a good performance of the device. The position of the anchor point from the elbow is hence an important optimization parameter along with the anchor position around the axis of the arm. The design of an exoskeleton to reduce reaction forces at joints due to misalignments in wearable devices has been presented in a study [46]. In another paper, the reaction forces at joints during the interaction of wearable devices with digital human models have been reviewed [47]. Studying the physical load on the wearer's body is important for designing a comfortable wearable device. The presented results study the change in reaction force at the elbow due to the anchor position from the elbow joint.