No need to add weight to this device to change the workload. The user controls the exercise by setting the resistance levels on the braking system and moving at a desired speed. A high caloric burn (~600-700 calories in 30 minutes) is possible at moderate resistance levels----with the user moving at 1.0 MPH. This is total body, minimal impact exercise, appropriate for the aging athlete, dynamic core stabilization, total body conditioning, sports medicine/athletic training applications and in physical therapy centers. Great for weight loss. Users can workout on consecutive days with no soreness.