## 5 Discussion
Unfortunately, the use of remoting and real-time data saving introduces a delay between the movement of the subject and the movement repeated by the skeleton. The movement captured by the Kinect is correct and can follow even a fast movement, such as a kick or a punch, but it is reproduced on Unity with a delay of about half a second. Furthermore, the system finds its greatest application when the subject has a fracture in the spine or a long bone. In these cases, the 3D reconstructions of the bones are directly built from their DICOM scans, and the fracture behavior can be studied during the sports movements. The percentage of fractures and dislocations to which Karatekas are subject should not be underestimated [49; 50]. In many cases, these are due to the incorrect execution of the basic position and stance assumed during a kick or a punch [51]. The adequate rotation of the foot, knee, and hips in a kick are essential to give more force and efficacy to the blow without suffering damage to the joint and bone to cushion the reaction force suffered on impact elegantly and correctly. Also, punches could be affected by the joint's wrong position. To better perform the punch, the wrist should be straight and parallel to the floor, the fingers might be correctly closed, and the punch's force is associated with the perfect rotation of the hips during the stance. The correct performance does not have a negative impact on the shoulder. Anatomical fidelity is important for this type of application, so caution and improvements are required. As documented in other studies [42; 43; 44], Kinect-based systems can have poor joint tracking when a body part is not visible to the camera and during unusual poses or interactions with objects. It is worth pointing out that in this work, the assessment is characterized by the subject sited frontally to the Kinect Azure camera, and the athlete did not interact with any object. Complex poses are behind the scope of this preliminary study. Future implementations can be carried out to correct or minimize the 3D reconstruction errors of the devices. Firstly, to effectively and immediately achieve the overlapping of the 3D anatomical components on the patient through the HoloLens viewer, the Kinect must be positioned as close as possible to the camera of the HoloLens device. In this way, the position detected by the Kinect could be used to locate the 3D reconstruction in MR correctly. In addition, \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Reference**[35] & **Reference**[29] & **Reference**[36] & **This Study** \\ \hline \multirow{7}{*}{System proposed} & 2 screens & 2D Pose estimation & & \\  & Laptop (2.8 GHz & 3D pose forecasting & & HoloLens 2 \\  & Pentium 4) & 3D recovery & & \\  & USB Cam & HTC Vive & Optica Motion Capture & Laptop \\  & OpenGL & Sony Camera & system & Azure Kinect \\  & OpenCV & DSC-QX10 & & Unity 3D \\ Markless & yes & yes & yes & yes \\  & nO & yes & no & yes \\ technology & Virtual Reality & Virtual Reality & Virtual Reality & Mixed Reality \\ IMU tracking & no & yes & no & yes \\ Motion Sickness & no & no & no & no \\ Data acquisition & no & yes & yes & yes \\ Feedback & Audio-visual & visual & visual & visual \\ Personalization & Not available & Not available & Not available & yes \\ External control & yes & yes & yes & yes \\ DICOM & no & no & no & yes \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparison of the systems used for supporting martial arts athletes. other application components can be implemented depending on the purpose of use, such as the viewing of medical images or the possibility of remote sharing. Finally, the Kinect can determine the position of the body joints, albeit with a certain margin of error. If the subject is stationary and with arms outstretched, the joints are correctly recognized, and the skeletal overlap is coherent. When the subject bends the elbow, bringing the hand towards the shoulder, the joint remains in the correct position.