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

Abstract

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 (Kleg) remains constant while vertical stiffness (Kvert) increases in able-bodied runners. The Kvert further depends on a combination of the torsional stiffnesses of the joints (joint stiffness; Kjoint) 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. Kleg, Kvert and Kjoint were calculated from kinetic and kinematic data in both intact and prosthetic limbs. Kleg and Kvert in both limbs remained constant when running speed increased, while intact limbs in ILEA running with RSPs have a higher Kleg and Kvert than residual limbs. There were no significant differences in Kankle, Kknee and touchdown knee angle between the legs at all running speeds. Hip joints in both legs did not demonstrate spring-like function; however, distinct impact peaks were observed only in the intact leg hip extension moment at early stance phase, indicating that differences in Kvert between limbs in ILEA are due to attenuating shock with the hip joint. Therefore, these results suggest that ILEA using RSPs have a different stiffness regulation between the intact and prosthetic limbs during running.

Characterizing the Mechanical Properties of Running-Specific Prostheses

“…When athletes with transtibial amputations run, they generate peak vertical ground reaction forces (GRFs) with their affected legs that are 2.1 to 3.3 times body weight at speeds of 2.5 m/s to 10.8 m/s [8,18,25,26]. During running, peak resultant GRFs typically occur around mid-stance and are oriented vertically.…”

Effect of step frequency on leg stiffness during running in unilateral transfemoral amputees

“…We calculated k leg as the ratio of F peak and ΔL (the ratio of F peak and Δy for k vert ) between ground contact (initial leg compression phase) and the instant of F peak 11,14,27,28 . Because body mass influences the stiffness 2 , both k leg and k vert were normalized to the subject's body weight (BW), which included the prosthesis.…”

Running-specific prostheses: The history, mechanics, and controversy

“…They found that the vGRF was significantly higher in the able-bodied athletes than in the double amputee sprinter. Similarly, several studies reported that the RSPs would impair force generation and thus likely limit top speeds 12,[14][15][16] .…”