This is a fundamental engineering research project directed towards the emerging technology of "power driven exo-skeletons". Engineering research is necessary now to determine the fundamental principles of control essential to produce devices which can be used to assist severely disabled persons in the future. When the muscles of a limb have become too weak to perform ordinary tasks, an exo-skeleton can be used to help assist the damaged limb and regain a measure of normal use. This research is also applicable to understanding the motion and loading of biological and robotic limbs.