## 5 Kinematic Assessment of Movement Performance
### Inertial Measurement Unit--IMU  
An IMU is a device manufactured using MEMS technology, and it is composed of more sensors, including an accelerometer, gyroscope, and magnetometer, working together to detect the acceleration rate and changes in rotational values, like pitch, roll, and yaw [114]. The features of IMUs can be identified from their Degree of Freedom (DOF), which is the number of values among axial accelerations that it can measure (e.g., a 10 DOF device that includes a tri-axial accelerometer, gyroscope, and magnetometer, plus an altimeter sensor is widely employed for drones' navigation control). Once fed into a microprocessor, it is possible to calculate the actual velocity and position using these data and proper integration procedures, given their respective initial values. Moreover, in some of the latest devices, an embedded high-performance processor enables the output of more detailed data based on the math of quaternions and Euler's angles [115] (Figure 5). These miniaturized inertial sensors are high-performance and can be considered a powerful alternative tool for measuring and analyzing sports movements [116; 117; 118]. In particular, the IMU validity and reliability were researched on the wrist movement in the pitching phase in both baseball and cricket games and the punching in boxing, trajectory of the joints or velocity and acceleration in the snow sports and disability games, including wheelchair basketball, by comparing via Motion Capture System (MOCap, further explored in Section 8) [114; 119; 120; 121; 122]. Additionally, accelerometers are used to measure the agility, acceleration, and prediction of prevailing foot trajectory movement in team sports, including volleyball and football [123; 124]. Additionally, the output of force sensors and the kinematic data obtained from IMUs were used to estimate jump height and ball impact timing in jump serve, block, and attack actions in volleyball coaching [125]. Another paper on long-distance running or triathlons reported measures on the modality of the foot support obtained by three-axis accelerometers placed on the back of the athlete near the lowest part of the spinal cord. By these sensors, they can assess the applied forces to the feet and study the cleat adjustment to determine acceleration magnitudes of the trunk [126]. Figure 5: IMU is a device composed of accelerometers, magnetometers, and gyroscopes that can reach 3D information on acceleration and rotational motions. It is possible to access acceleration, angular velocity, and orientation graphs. On the other hand, the capture motion methodology cannot accurately provide fundamental quantities such as velocity and acceleration (hence, forces and torques) during high-speed motion, which is typical of many sports. Studies conducted on baseball illustrate that using IMUs is a valid method for quantifying the mechanism of generating the pitching ball's speed. IMU sensors were attached to the upper torso, arm, forearm, and hand segments. The movement of a baseball pitcher who was asked to throw to the target was measured with a combined Mocap and IMU system. The results detected by the quantitative analysis of the ball speed generation mechanism with the proposed method do not show inconsistencies with that performed by the Mocap system [127]. Another study compared the IMU (Xsens brand) with the Vicon optical MoCap system in the acquisition of walk, squat, and lateral lunge movements. The positioning of the joint heads in Xsens followed the trajectory of the Vicon data with a good approximation. Xsens can be a valuable alternative to the Vicon system, but it still has not produced clinically beneficial outcomes. Indeed, to collect meaningful data in the clinical study, it should be treated cautiously for a sizeable joint movement [128].