Quantitative analysis of the human ankle viscoelastic behavior at different gait speeds

Abstract

Human ankle joint has viscoelastic behavior. Two components of viscoelastic stiffness have been defined as quasi-stiffness and hysteresis. Quasi-stiffness is the slope of the ankle moment-angle curve during walking. Hysteresis is the area between loading and unloading curves. Numerous studies have shown that viscoelastic components vary as gait speed changes. The aim of this study was to quantify the quasi-stiffness and hysteresis components of viscoelastic stiffness in different gait velocities during walking. Ankle kinetic and kinematic data of a healthy young male were collected in three levels of walking speeds using VICON motion analyzing system and Kistler force plates. Ankle angles, moments and powers were computed using VICON Workstation software. Based on moment-angle curves quasi-stiffness and hysteresis were quantified. At slow walking speed, hysteresis loop was clockwise. At normal speed hysteresis was nearly zero and in fast velocity hysteresis loop changed to counter-clockwise direction. Spearman correlation coefficient showed significant positive correlation between gait velocity and quasi-stiffness (p<0.005). The correlation between walking speed and hysteresis was also significant (p<0.005). Therefore in designing prosthetic ankles, the effect of walking speed on quasi-stiffness and hysteresis should be considered. © 2011 Springer-Verlag.