This study analyzed three dimensional (3D) in vivo kinematic data from the squatting to standing position for 18 Japanese subjects (18 knees) implanted with either Legacy((R)) Posterior Stabilized (LPS) Flex Fixed Bearing TKA or LPS Flex Mobile Bearing TKA. Under weight-bearing conditions, for all patients, the average roll-forward motions for the medial and lateral condyles were 4.0+/-3.6 mm and 6.3+/-3.4 mm, and the average external axial rotation was 3.1 degrees +/-4.1 degrees . For both groups, the weight-bearing range-of-motion (ROM) (110.7 degrees +/-12.7 degrees ) was less than pre (127.2+/-15.5 degrees ) and post (135.6+/-5.4 degrees ) operative non-weight bearing ROM. As hypothesized, the incidence, average and maximum lift off for the squatting to standing activity were much less than those of deep knee bend (DKB), and condylar motions and kinematics were opposite that of the DKB. There was little statistical difference of their kinematic patterns during this activity between the LPS fixed and mobile TKA implants.