## 7 Motion Capture Systems--MoCap
### Markerless Video Analysis
The Kinect MoCap method is a markerless video analysis system initially produced by Microsoft in 2010. Kinect sensors provide new and improved capabilities for motion detection and 3D reconstruction. Its software automatically scans the scene and carries out the segment and players' tracking employing depth cameras and laser scanners [244]. It has IR detectors and emitters to capture human physical activities. The critical components of Microsoft Kinect sensors are RGB cameras, IR depth sensors, and multiple microphone arrays. Kinect v2 has better features than the previous version, such as better resolution, image recognition, and broader area view. A further significant part is that Kinect v2 has better skeletal joint tracking and can capture twenty-six joints, while Kinect v1 can capture twenty joints [245]. This system was initially developed within the scope of the gaming and entertainment fields, but it later proved highly interesting in sports, clinical, and rehabilitation applications [246; 247; 248]. Kinect sensors also introduce many features that allow for more accurate research on the movement of the human body and its gestures. Through its use, the coaches can access real-time data, compare the motion data, and understand the player's motion in an animation reproduction [249]. The central part of the Kinect (Microsoft released Xbox360 game console peripherals, Kinect) software is the skeleton recognition, joint positioning, adaptation to human movement, and body-tracking capabilities of two people simultaneously (Figure 11). The depth camera can provide helpful support to the analysis by avoiding background parameters disturbing the process of participants' motion recording [250]. Microsoft Kinect is a non-invasive sensor essential for medical diagnostic and therapeutic purposes and a valuable tool for gait abnormalities, postural disturbance analysis, and physiotherapy. It can also help monitor the progress of patients undergoing rehabilitation. In sports, to create a dataset of fencer movement and action during the fencing competition, the Kinect software system was used to reach real-time feedback for the speed performance and slow-motion fencer's body slow motion, motion recordings, and analysis of body and sword movements in both offensive and defensive modes [245]. Likewise, in the clinical setting, the Kinect is used to analyze the joint for natural human actions and pieces of training, such as single-leg squats. Some facilities of Kinect in clinical analysis include calculating the net trajectory angle and estimating the best-fit line in squat movement in lateral or medial movements [251]. A recent study evaluated the validity of a markerless 3D full-body motion tracking method based on a single RGB-D camera compared to a gold-standard marker-based system. Twenty-three children and young adults performing different movements using a Microsoft Azure Kinect RGB-D camera version 1.1.2 and multi-camera Vicon Nexus 2.10 system simultaneously have been recorded. It seems to have a satisfactory accuracy most of the time and is close to the gold-standard system but not indicated for clinical motion analysis [252].