A body weight support system that monitors and controls the level of support force within a stepcycle to result in normative center of mass movement and ground reaction forces. The system comprises a harness (2) connected to a lift line which in turn is connected to a means (20) for advancing and retracting the lift line. A control system (12) is configured to monitor load on the cable (4) and to regulate lift line advancement and retraction in response to load information. The support system can be combined with a treadmill (28) for locomotor training of a subject.