## 3 Experimental Results
### Results Using the 'First' Part of the Dataset  
In Figure 3, the predicted 3D human skeleton during the arm flexion exercise is illustrated. The first row displays key frames from the front video stream, while the second row shows frames from the side video stream. The third and fourth rows present the corresponding 3D skeletal reconstructions. The red 3D skeleton represents the front-view projection, and the blue skeleton corresponds to the side view, both before alignment. The pink skeleton is the final result after alignment. The illustration reveals that the front-view projection has a depth error, with the upper body appearing tilted forward and the lower body tilted backward. Similarly, the side view misses joints on the left side. The final 3D skeleton corrects these issues, although a depth error persists in the left hand. Figure 4 shows the variation in depth coordinates during the first upper arm flexion test. The focus is on the right elbow and wrist joints since these undergo the most significant depth changes. Between frames 40 and 90, the video synchronization signal flattens, and the exercise begins at frame 100. The largest depth error occurs when the arm is raised, yet the overall trajectory remains consistent. The final result shows smoother and more centered joint depth trajectories along the Y-axis. Figure 4: Depth coordinate changes during upper arm flexion (Test 1): (**a**)—right elbow joint; (**b**)—right wrist joint. Figure 3: An illustration of the result of the 3D human skeleton for flexion of the upper arm in the first dataset. The second test of upper arm flexion is depicted in Figure 5, again focusing on the right elbow and wrist joints. Here, video synchronization occurs between frames 35 and 85, with the exercise starting at frame 95. The depth error is most pronounced when the arm is raised, but the trajectory is similar to the first test, with smoother and more centered depth trajectories in the final result. In the third upper arm flexion test, shown in Figure 6, the focus remains on the right elbow and wrist joints. Video synchronization occurs in frames 1-50, with the exercise starting at frame 70. The depth error peaks when the arm is raised, yet the joint depth trajectories in the final result are smoother and more centered, mirroring the results of the previous tests. Figure 7 illustrates the depth coordinate variations during the fourth upper arm flexion test, again focusing on the right elbow and wrist joints. Synchronization takes place between frames 35 and 80, and the exercise begins at frame 110. The largest depth error occurs when the arm is raised, but as in previous tests, the final result shows smoother and more centered joint trajectories. For standing upper arm flexion exercises, the right elbow joint shows a mean error ranging from 0.0611 m to 0.0855 m with standard deviations ranging from 0.0391 m to 0.0652 m. The errors in the right wrist joints are greater, ranging from a mean of 0.0884 m to 0.1344 m with standard deviations between 0.0648 m and 0.0964 m.  
Figure 5: Depth coordinate changes during upper arm flexion (Test 2): (**a**)—right elbow joint; (**b**)—right wrist joint. Figure 6: Depth coordinate changes during upper arm flexion (Test 3): (**a**)—right elbow joint; (**b**)—right wrist joint. In Figure 8, the predicted 3D skeleton is presented during the arm adduction exercise. The red skeleton from the front view and the blue skeleton from the side view both show significant depth errors before alignment. The final pink skeleton corrects these issues, but a residual depth error is noticeable on the left. Figure 9 shows the depth coordinate variations during the second upper arm adduction test. The right elbow and wrist joints again serve as focal points. Synchronization takes place between frames 25 and 70, and the exercise begins at frame 90. A consistent depth  
Figure 8: An illustration of the 3D human skeleton of the retraction of the upper arm in the first dataset.