The sit-to-stand (STS) movement is important in improving satisfaction after total knee arthroplasty (TKA). Reports on motion analysis using a combination of motion capture systems, force plates, and surface electromyography after TKA are limited. We aimed to compare the STS movement of patients aged over 60 who underwent modern and conventional TKA with more than 6 months of postoperative follow-up. Ten patients underwent surgery with a modern implant (Group I: Smith and Nephew JOURNEY II, Memphis, TN, USA), and ten with a conventional implant (Group II: Smith and Nephew LEGION, Memphis, TN, USA). STS movement kinematics and kinetic data were measured by synchronising a motion capture system with a force plate. Surface electromyography was used to measure the muscle activity. STS time was shorter in Group I than in Group II. Maximum knee-extension angular velocity and maximum knee-extension moment were greater in Group I than in Group II. Electromyography revealed that Group I tended to have less activity in the quadriceps femoris than Group II. Group II had a greater hip-extension moment and vertical ground reaction force, and the hip joint seemed to compensate for knee function. Group I possibly used the quadriceps muscle more effectively, due to the implant shape.