An assembly for stabilizing an individual while exercising in a seated position, such as, but not limited to, a wheelchair. A harness assembly comprises a plurality of harness structures each intended to be removably secured to a different part of the individual's body in a manner which stabilizes that body portion while performing a particular exercise. A restraint assembly comprises a plurality of restraint members interconnected to each of the plurality of the harness structures being used and to an anchor assembly, disposed in underlying, supporting relation to the individual and the support structure. The restraint assembly is cooperatively structured with the anchor assembly to maintain any of the harness structures being utilized and the corresponding body portion in a stable, operative position best suited to effectively perform the intended exercise.