The second phase of this pilot study will be a controlled trial of three-month progressive aerobic Lokomat exercise in chronic incomplete spinal cord injured subjects. The aim of this trial will be to determine whether progressive Lokomat training will improve cardiovascular fitness and ambulatory function when compared to matched impairment severity CMISCI subjects receiving the same duration of usual physical therapy care. Thirty-six subjects will be recruited into this phase of the study. Open spirometric evaluation of cardiovascular parameters as outlined in phase one of the proposal will be measured at baseline, 1 months, and 3 months. Initial, six-week and post-study ambulatory function evaluations including the WISCI (Walking Index for Spinal Cord Injury), a timed 10 meter walk, a measured walk over 6 minutes, and a gait analysis will also be determined. It is hypothesized that aerobic Lokomat exercise will improve cardiovascular fitness as determined by an increase in VO2 (oxygen consumption) peak and improve function as determined by timed walks and gait parameters in these subjects. The results of this pilot and development study will provide the necessary information to design larger randomized clinical trials.