## 4 Discussion
The reason for placing three other sensors in the anterior distal, medial distal, and lateral distal locations was to ensure coverage of the main areas close to the one from which we expected to be able to retrieve information about fluctuations in the volume of the residual limb. Moreover, we decided to carry out the experiments with a limited number of sensors to maintain a simple setup and limit the amount of wiring to ensure the practicality of running the test with participants. Although more sensors could be used in preliminary tests and for short term solutions, there were requests from clinicians to minimize the number of sensors to assure practicality of using the method in long term applications of the system. The experimental results of our work confirmed our hypothesis regarding the number and placement of the sensors. Although the labeling of data was performed manually based on video recordings, this procedure was accurate as the beginning and the end of each step were confirmed with the FSR-sensor data. The manual labeling was performed only to remove the steps performed by the users to turn around in between repetitions. Moreover, small errors in labeling would cause missing FSR data in the beginning of the first step or at the end of the last step of a repetition which would not affect the result since the outcome measure was based on the peak of FSR values which occurred mid-step. As a result, we believe that manual labeling of data has not affected the results obtained in this study. The reason that the force at the anterior distal, medial distal, and lateral distal locations did not follow the expected pattern in the three-ply phase might be that for those locations, sensors were placed more proximally compared to the distal location. This makes these locations more prone to variations in interface pressure that are caused by user's socket fit, style of socket, and movements of the limb inside the socket. For example, depending on the shape of the residual limb and the relative location of the Tibia bone, the pressure distribution at the anterior location could vary in different individuals. On the other hand, all users were using non-distal-bearing sockets which made the pressure at the distal location more consistent. Moreover, an increase in the volume of the limb results in an increased width/diameter of the limb which could affect the more proximal locations. Results obtained for participant 2 in the one-ply phase demonstrate high inter-participant variability between this individual and others in this phase. Inter-participant variability in the distal pressure can be caused by multiple factors such as the user's wight, the shape and the type of the socket, the socket fit, and the shape of the residual limb in addition to whether prosthetic liners are used or not. Participant 2 of the second phase used a gel sock instead of a prosthetic liner which, in addition to other differing factors including the type of the socket and the shape of the limb, has likely influenced this participant's measurements. Another reason for such measurement differences is possibly the fact that this participant had suffered a foot injury in their intact limb a few months prior to the experiment. Nevertheless, the pattern of variation in the distal force remained as expected for this participant. This demonstrates that the distal pressure decreases with an increase in the volume of the limb regardless of individual-specific factors mentioned above. Although force measurements in three out of the four locations tested in the three-ply phase did not demonstrate the expected pattern of variation in response to changes in the volume of the limb, noting that the initial hypothesis of this study was based on distal force, results of the three-ply phase confirm this hypothesis. It should be noted that the other three sensors in the three-ply phase were only added to ensure coverage of the main areas that were close to the distal location and were expected to experience greater pressure/force changes.