1. A motorized ankle prosthesis, orthosis or exoskeleton apparatus, comprising: an actuator operatively coupled to a joint; at least one sensor for determining a parameter that correlates with gait speed; a controller in communication with the at least one sensor, the controller configured to cause the actuator to deliver to the joint over a gait cycle an amount of net ankle work that increases with increasing gait speed, the controller further configured to calculate net ankle work applied to the joint over the gait cycle; and an interface in communication with the controller, the interface configured to display information regarding the calculated net ankle work applied to the joint, to receive an input from an external source and send a signal based on the received input that causes the controller to change net ankle work over the gait cycle applied to the joint as a function of gait speed.