The analysis of human walking stability using ZMP in sagittal plane

This paper investigates the difference of walking stability between the young and the elderly by using the method of zero moment point(ZMP) in sagittal plane. 3 young subjects and 3 elderly subjects participated in free walking experiment in a straight line on level ground. Motion capture system was used to collect the experimental data of lower limbs movement while walking. Experimental results show that in the comparison between young and elderly, there are some effective walking stability parameters, specifically including the horizontal distance (δ_Zmp) between ZMP and the center of mass of body, the horizontal distance (δ_ankie) between ZMP and the ankle joint, the linear relationship between δ_ZMP and gait speed, and the trajectories of ZMP in ground plane. These parameter criteria can be used to analyze dynamic walking stability for guiding the development of walking assistance devices.

I. Introduction

Aging has increasingly become a social problem throughout the world [1]. It is estimated that by 2050 the elderly population will reach nearly 2.1 billion people in the world [2]. Against such a background, a concern regarding the health care of elderly persons for preventing progression to frailty and nursing care is attracting growing attention [3]. It is known that walking ability, which is closely related to the quality of elderly life, is one of the most important in human daily activities. On the other hand, it is reported [4] that at least 30% of persons aged 65 and above, due to the decline of age-related lower limb muscles, suffer walking difficulties. Researches have shown that gait and balance disorders or weakness are the second reason in causes of falls in elderly people [5]. The falls will not only affect the quality of the elderly's life, but also increase economic burden of the family and society. Some elderly people are not willing to walk outdoors because they are afraid to fall. Therefore, large numbers of the elderly people with weaken leg to walk are in need of walking assistance device to overcome their walking obstacles [6].