The Pilates-based reformer is used by dancers for training and for injury rehabilitation. Knee kinematics and applied forces during demi-plié in fifth and in first positions were analyzed while dancers performed the motions (a) standing, (b) on the reformer equipped with two springs, and (c) on the reformer equipped with four springs. The highest forces, normalized to body weight, were obtained for the standing demi-plié, while the largest knee flexion angles occurred on the reformer with four springs. Greater range of motion was achieved in first position than in fifth, and females exhibited greater extension and higher normalized forces than males, It was also noted that force/knee angle relationships for the standing demi-plié and for the reformer tests were quite different. Reformer forces were totally dependent on the knee angle, whereas the forces during the standing demi-plié depended on the acceleration of the dancer's center of gravity.