We used multiple measures to compare the control of the 3- and 6-DOF prostheses. Because the motors of the prosthetic system did not have encoders available for recording the position of the arm in space, the kinematics were monitored using a passive motion capture system.f To track 3-dimensional joint motion, 3 infrared reflective markers were placed on each rigid segment of the 6-DOF prosthesis, including the socket, the upper arm, the forearm, and the hand (fig 2). Two additional markers were placed on the tip of thumb and index finger of the prosthetic hand for calculating the hand open and close motions. In total, 14 markers were applied and each marker’s position was tracked by 6 infrared sensitive cameras at 120Hz sampling rate. The position of markers was smoothed by a sixth-order Butterworth low-pass filter with the cutoff frequency at 18Hz and the joint kinematics of the prosthetic arm were calculated.11 The prostheses were compared to quantify the workspace. In order to evaluate the ability to control joints simultaneously, other tasks performed included: drawing a circle in the frontal plane with the hand, reaching out and up with the arm (to mimic retrieval of an object from a high shelf), pulling back the arm from that reaching position and coordinated movements involving hand open and close and elbow flexion and extension