# Single Camera-Based Remote Physical Therapy: Verification on a Large Video Dataset
## 4 Discussion  
The main objective of our research was to determine the usability of a camera-based system in a home environment. Since human position detection is captured by only one RGB camera, we were mainly interested in the influence of camera view and the position of the trainee, where we expected the greatest impact on the detection of keypoints. The quality of detection was determined by the confidence of detection of each keypoint. Our main findings are the following: regardless of the camera view, the lying position comes out as the least detectable, followed by the position on the knees. The standing position is the most efficient, but the absolute differences against the sitting position are small. In the case of the camera view, the results were not so convincing. For the lying position and the position on the knees, the differences are not statistically significant in most cases, but no conclusions can be drawn because of the large variances. For standing and sitting positions, the camera view from the side is a bit worse. From the data we have available, it is not possible to give a clear answer to the question of whether the confidences for the different camera views differ. We also found out the difference in confidence between upper-body and lower-body keypoints. Confidence of lower-body keypoints is generally lower. This can be explained by the fact that the positions of the upper limbs are more variable than the position of the lower limbs. Generally speaking, joint positions are easier to establish if they are at an angle other than 180 degrees, which is typically the angle of the knee. The hips are not as visible as the shoulders and the ankles are often covered by shoes and trousers, while the position of the wrist can be very easily derived from the palm of the hand. We can justify generalizing the results about views and postures given the high number of unique exercises, as opposed to works focusing on specific exercises, where only a few different types of exercises are involved. Before applying the research results in practice, it is important to define several assumptions and limitations. They are closely linked to the application area of telerehabilitation in home settings. The first assumption and limitation at the same time is the use of a single simple camera (smart phone, tablet). The second assumption is the application use by nontechnical users that results in the requirement of simple control and setup of the application. These considerations led us to experiments analyzing the influence of the body position in relation to the camera and evaluation of many different exercises recorded by a single camera. Figure 9: Confidence of detection of selected KP (keypoints)—side view, lower body. Camera views are shown in colour as follows: lying down (\(N=215\)); on the knees (\(N=92\)); sitting (\(N=145\)); and standing (\(N=297\)). All the other differences are statistically significant. Only differences that were not statistically significant (n.s.) are highlighted in the boxplots. In the light of these facts, we are well aware of the limitations of the proposed approach, in particular the precise identification of certain motions in the front or side view. For example, abduction of the right arm cannot be well recognized in the side view from the left side, the range of straddling backward or angle of the knee cannot be precisely identified in frontal view. For practical usability, it is important that there are not too many dropouts, i.e., that the joints are detected, and that they are not mistaken with another part of the body, e.g., the left and right limbs are swapped when viewed from the side, and so on. Another important aspect of the evaluation is that each individual exercise engages different parts of the body, thus only certain points are important for the analysis of the given exercise. The camera view is chosen so that the parts of the body being exercised are clearly visible while at the same time some parts of the body can be obscured.