 Subjects must be capable of repeatedly walking 15m independently and unsupervised. They must be co-operative and able to follow commands and have adequate natural step and stride lengths to step on three force plates in series. Subjects must have a combined lower limb size shank and foot that results in a PD-AFO size within the prototyping capacity 50 cm of the selective laser sintering machine. To participate in the impaired study, subjects must have a manual muscle strength score for plantarflexion strength that is less than or equal to three out of a five point scale. 