Purpose- Recent developments of durable flexible materials and their application to the prosthetic foot has provided a means of overcoming the rigidity of the solid ankle of the standard SACH foot while preserving durability. While below-knee (BK) amputees express a preference for the more dynamic feet over the standard SACH foot, subjects in our pilot work failed to demonstrate significant functional differences in the foot designs studied, which indicated that the discriminating parameters perceived had not been measured. Therefore, we have designed a more comprehensive research program based on the responses of the subjects in the pilot project and in work conducted by other laboratories.