Amputee locomotion: Spring-like leg behavior and stiffness regulation using running-specific prostheses

Carbon fiber running-specific prostheses (RSPs) have allowed individuals with lower extremity amputation (ILEA) to participate in running. It has been established that as running speed increases, leg stiffness (K-jeg) remains constant while vertical stiffness (K-vert) increases in able-bodied runners. The K-vert further depends on a combination of the torsional stiffnesses of the joints (joint stiffness; K-joint) and the touchdown joint angles. Thus, an increased understanding of spring-like leg function and stiffness regulation in ILEA runners using RSPs is expected to aid in prosthetic design and rehabilitation strategies. The aim of this study was to investigate stiffness regulation to various overground running speeds in ILEA wearing RSPs. Eight ILEA performed overground running at a range of running speeds. K-leg, K-vert and K-joint were calculated from kinetic and kinematic data in both the intact and prosthetic limbs. K-leg and K-vert in both the limbs remained constant when running speed increased, while intact limbs in ILEA running with RSPs have a higher K-leg and K-vert than residual limbs. There were no significant differences in K-ankle, K-knee and touchdown knee angle between the legs at all running speeds. Hip joints in both the legs did not demonstrate spring-like function; however, distinct impact peaks were observed only in the intact leg hip extension moment at the early stance phase, indicating that differences in K-vert between limbs in ILEA are due to attenuating shock with the hip joint. Therefore, these results suggest that ILEA using RSPs has a different stiffness regulation between the intact and prosthetic limbs during running. (C) 2013 Elsevier Ltd. All rights reserved.