This allows for the six degrees of freedom of the knee joint to be flexed and extended and the varus and valgus to be internally and externally rotated, as well as the relative position of the femur and tibia and the state of contact between the femoral component and the insert. In addition to normal knees, kinematics evaluation of TKA patients' knees is widely performed. Many studies have revealed that, after TKA surgery, patients exhibit joint movements different from those of normal knees, called paradoxical motions, which are abnormal forward movements of the femur during knee flexion. It has also been reported that the medial pivot motion, which is the rotational movement of the knee joint around the medial femoral condyle that is observed in normal knees, is attenuated following TKA [28; 29]. While this 2D-3D registration method can evaluate precise kinematics of the knee joint, it has drawbacks, such as limitations in the imaging range, effects of X-ray exposure, and mechanical evaluation difficulty. There are three main types of motion capture systems: optical, magnetic, and inertial sensors, but optical motion capture is the most commonly used. This is a dynamic analysis method that involves attaching infrared reflective markers to the body surface, photographing them with an optical camera, and analysing their trajectories. Although equipment is required for measurement, any movement can be evaluated within the measurement space, and kinematics evaluation is possible without invasiveness or X-ray exposure. Although it is widely known for its use in creating computer graphics for movies, it is often applied in the field of orthopaedics as a kinematic analysis method for sports movements and ADL [30; 31]. A ground-reaction-force sensor is a device that can measure the ground reaction force that counteracts gravity from the soles of the feet. By synchronising the motion capture system and the ground-reaction-force plates, kinematics such as joint positions and joint-motion angles, angular velocities, and angular accelerations can be calculated, and joint moments and kinetics can be calculated from the relationship with the ground-reaction-force vector. Although this method is inferior to the 2D-3D registration method in terms of accuracy, it is useful in that there are no restrictions on movement, and, in addition to kinematics evaluation, it is possible to estimate mechanical loads on the body and joints. ADLs such as walking, standing up, and climbing stairs have been analysed for healthy subjects, patients with knee OA, and patients after TKA surgery. Although patients after TKA have improved walking and standing movements compared to those of patients with knee OA, their walking ability, such as walking speed, decreases compared to that of healthy individuals, and they exhibit abnormalities in knee-joint-extension moment and varus moment [32; 33; 34; 35; 36; 37]. One motion analysis method is electromyography. An electromyogram records and displays the myoelectric potential that causes muscles to contract. Surface electromyography evaluates muscle activity by pasting electrodes on the skin, making it possible to estimate muscle tension and muscle fatigue in a minimally invasive manner. It allows for static evaluation and the examination of changes in biological functions during movement, and is used in fields such as sports, rehabilitation, and ergonomics. With the development of multi-channel and wearable measurement equipment, as well as advances in signal processing methods and analysis tools, evaluations are becoming easier and more precise. Previously, surface electromyography analysis of ADL, such as walking and standing up, was performed on patients after TKA surgery [38; 39]. It has been reported that in patients after TKA, the quadriceps muscle becomes abnormally overactive during walking or standing up, and co-contraction with the hamstrings occurs [39; 40]. Therefore, we focused on motion analysis using motion capture, force plates, and surface electromyography.