# Donning/Doffing and Arm Positioning Influence in Upper Limb Adaptive Prostheses Control
## 3 Results
### Arm Position Experiment  
The arm position experiment was developed to test the robustness of a model in unknown arm positions (different to the trained one) and also to study if any of the training positions obtains better results. The mean values for each metric, training and testing position are shown in Figure 8. The free arm positioning was called P4 to simplify the notation. Figure 7: (a) Path for test 5 for subjects 1 (red) and 5 (green) for the first five targets. This is a comparison between a high PE and a lower PE value. Green path shows a more erratic behavior reaching a lower PE value as the red path follows an almost straight trajectory from target to target with a high PE value. (b) This is an attempt ratio value example showing the stability of the controller to maintain a position. Red line corresponds to subject 1; green line corresponds to subject 3. The subject 1 entered the target 2 and remained inside at the first try. Opposed to this, subject 3 entered and left the target two times until the target was missed. The participant, in this occasion, was not able to maintain the position having a less stable control measured by the attempt ratio value. Figure 8 plots the data for every test. Our results clearly show that the performance is high regardless the learning position or the training position. The minimum \(\text{CR}=89.58\%\) is obtained for the model trained in P3 when tested in P2; the rest of the CR values are above 91%. The PE values are also high independently of the combination, with PE \(\geq 83\%\). The system was robust against arm positioning variations. Figure 8 also shows that the trend inside each training arm position is consistent with all the different training options, i.e., the bars follow a similar pattern for all the training arm positions. This confirms that the results were independent of the training position. The results in Figure 8 indicate that P1 was the best testing position. Position P1 (red bars) performed slightly better than P2 (green bars) and P3 (blue bars) in almost all metrics, independently of the training arm position. We applied the non parametric Friedman test for repeated measures to each training position. The results revealed a statistically significant difference for the PE metric with values of \(p=0.0112,0.0129,0.0194\) for the three different training positions. A posterior multiple comparison test indicated that the difference was between testing in P1 and testing in P4 (free movements) in all cases. After ranking the PE for the different training positions, P1 was always ranked in the first place and P4 in the last position in all experiments except one. We also observed qualitative results related to the effect of fatigue and usability. All the patients reported ending up very tired after performing the test in P3. Holding the arm straight generated shoulder fatigue that did not allow the patients to keep a consistent performance. Some participants even stopped at some point to relax the arm. This observation is related to the quantitative results seen before, where P3 tests have lower PE values training in P1 an P2. This effect was mitigated when P3 was the training arm position because the fatigue was included in the training information. The yellow bars in Figure 8 give information about the system robustness against arm position changes within short periods of time (P4). These tests were performed allowing the users to move the arm with no restrictions at all, making every test unique and, therefore, not comparable with any other test. In any case, the results showed that all the metrics had an expected drop in this dynamic and uncertain scenario. The user adaptation was proven to be essential in this case. The participants managed to maintain a high performance (CR = 90.28% and PE = 80.13% on average). However, the system and the user needed a moment after changing the arm position to adapt to the EMG variations of it.