2. Motor Control Test Protocol The Motor Control Test (MCT), using the same apparatus will be performed to examine postural responses to external perturbations. During the MCT, subjects will receive perturbation from the force platform. Perturbations are expressed as translation movement (medium horizontal anterior to posterior movements of less than 1 sec. duration) or as rotation movements (at 6.0 degrees per second, which cause ankle dorsiflexion or plantarflexion). Six forward and six backward translations are generated. Five toes up and five toes down rotations are generated. The computer assures random delays of 1.5 to 2.5 seconds between translation trials and 3.0 to 5.0 seconds between rotation trials. During each perturbation, the computer monitors the subjects sway responses, measuring forces exerted against the dual force plate. These forces are expressed as weight symmetry and strength symmetry. Weight symmetry measures the distribution of total body weight over each leg, independent of other response strength and strength symmetry measures. Weight symmetry scores near 100 indicate a symmetrical weight distribution (EquiTest manual, 1991).