BACKGROUND: . This study investigated whether loading the legs during the swing phase of walking enhances flexor muscle activity in ambulatory patients with incomplete spinal cord injury (SCI). METHODS: . Nine patients had surface electromyography (EMG) and joint kinematics recorded from the lower extremities during treadmill walking. Swing phase loading of the legs was achieved by weights (1-3 kg) attached to each lower extremity or by a velocity-dependent resistance applied by the Lokomat robotic gait orthosis. RESULTS: . When patients walked with the weights, there was a consistent increase in the activity of the knee flexors and sometimes of hip or ankle flexor activity during swing. Similarly, when the robot applied the velocity-dependent resistance during walking, swing phase flexor EMG activity tended to be greater. Enhanced knee flexion was observed in all patients after the weights or the robot-generated resistance was removed. CONCLUSIONS: . Flexor muscle activity during swing can be enhanced through additional proprioceptive input in patients with incomplete SCI with brief aftereffects. Further testing of this strategy is necessary to determine if it can improve the gait of ambulatory patients.