Ankle push-off power plays an important role in healthy walking, contributing to center-of-mass acceleration and swing leg dynamics, and accounts for 45 percent of leg power. Most passive energy storage and return prostheses for people with transtibial amputations are stiffer than a biological ankle, particularly at slower walking speeds. Additionally, passive devices provide insufficient levels of energy return and push-off power, negatively impacting biomechanics of gait, the authors of a recent study wrote.
With that in mind, they evaluated the kinematics and kinetics of walking with a microprocessor-controlled, variable-stiffness ankle-foot prosthesis (945g) compared to a standard low-mass passive prosthesis (Ottobock Taleo, 463g) with seven participants who had unilateral transtibial amputations. The results demonstrated the potential for a quasi-passive microprocessor-controlled variable-stiffness prosthesis to increase push-off power and energy return during gait at a range of walking speeds compared to a passive device of a fixed stiffness, according to the study.
By modulating prosthesis stiffness under computer control across walking speeds, the researchers concluded that there exists a stiffness that increases prosthetic-side energy return, peak power, and center-of-mass push-off work, and decreases contralateral limb peak ground reaction force compared to the standard passive prosthesis across all evaluated walking speeds, the authors wrote.
They found a significant increase in center-of-mass push-off work of 26.1 percent, 26.2 percent, 29.6 percent and 29.9 percent at 0.75 m/s, 1.0 m/s, 1.25 m/s, and 1.5 m/s, respectively, and a significant decrease in contralateral limb ground reaction force of 3.1 percent, 3.9 percent, and 3.2 percent at 1.0 m/s, 1.25 m/s, and 1.5 m/s, respectively.
The open-access study, “Variable-stiffness prosthesis improves biomechanics of walking across speeds compared to a passive device,” was published in Nature.
