Evaluation of the Probability of Motion Realization by Kernel Density Estimation Method in Human Walking and Comparing it with the Criterion of Margin of Stability

In studies with a quantitative approach to human walking stability, it is essential to quantitatively know how good the balance is at a body posture or every moment along a path. To predict and maintain a stable situation, it is necessary to develop a method that can measure stability and indicate the condition of dynamic balance along the path. In this paper, a new measure of postural stability was presented called the probability of motion realization based on the kernel density estimation, which assigns a value to the body motion based on the avoidance of a fall along a path. The issue of balance maintenance was examined for a population sample using a database and a motion capture technique for recording kinematic information of the gait cycle, and the probability of successful balance maintenance was calculated for the population. In addition, the probability of motion realization was calculated through a seven-link body model in all states for three age groups of men and women at different step lengths. The results were compared to the margin of stability, which is a conventional metric. The findings demonstrated that the margin of stability may be very low for a path on which most people can maintain their stability easily, whereas the probability of motion realization is high.