Human walking analysis based on fourteen-linkage walking model

Gait analysis is fascinating because of its highly interdisciplinary nature and wide range of applications. Human walking analysis is one of the most basic tasks that people seek to understand well because it is the locomotion taken most frequently than other movements, such as running, stair ascent, stair descent, and jumping, except for some static activities such as sitting, standing and lying. Walking is the most important locomotion in his daily life. It has been investigated that, a European, who lives in modern city, walks about 80500km averagely in his/her whole life. He/she walks 3150m per day.

More and more researchers have been interested in walking analysis for health management of elderly people. Before understanding pathological gait, it is necessary to understand normal gait, since this provides a quantitative standard to judge or evaluate the gait of a patient. Various methods are used to overcome the difficulties imposed by the extraction of human gait features. Two approaches are being used for human gait analysis: model-based and non-model-based methods.

The non-model-based method is applied in image based gait analysis (marker-less analysis). Feature correspondence between successive frames is based upon prediction, velocity, shape, texture and color. Small motion between consecutive frames is the main assumption, whereby feature correspondence is conducted using various geometric constraints.

For the model-based methods, a priori shape model is established to match real data to this predefined model, and thereby extracting the corresponding features once the best match is obtained. Stick models and volumetric models are the most commonly used methods. The model-based approach is the most popular method being used for human motion analysis due to its advantages. It can extract detailed and accurate motion data.

Many model-based methods are proposed for different research targets, such as Pendulum model, 5-link biped locomotion human model, six segments model, 7-ellipse model, 2D stick figure model with 7 segments, 10 stick figure model, stick figure with 12 rigid parts, hierarchical structural model with 15 points, 14 elliptical cylinders model.

Walking is a complex dynamic activity. A good human model for gait analysis recognition should be simple, but general enough to capture the dynamics of most walkers. Almost existing models, which have from 2 segments to more than 15 segments, have two pitfalls. Firstly, they paid more attention to the sagittal plane, and overlook the other two planes, transverse plane and frontal plane. Secondly, it is not enough to describe the particularity of the feet. Most of them regarded the foot as a point. If so, it is difficult to decide the gait cycle, such as initial heel contact, heel rise, and toe off.

We suggest a Fourteen-Linkage Walking (FLW) model, which is a collection of 19 points, 14 segments and 12 joints used to specify the position and the configuration of a human body. Position describes the location of a body segment or joint in space, measured in meters. In this model, the 19 points can be decided by the 30 markers we measured from motion capture system. Body segments are considered to be rigid bodies for the purposes of describing the motion of the body. 14 segments are composed of these points, such as head, shoulder, upper-arms (2), forearms (2), trunk, pelvis, thighs (2), shanks (2), and feet (2).

In this paper, the features of walking stability are then defined and extracted based on the FLW model. Two kinds of stability features, footprint features and walking cycle features, are researched. To evaluate the walking pattern, a new concept, stability coefficient, is suggested in this paper also. Our results show that the footprint and walking cycle features have close correlation with ages. FLW model is properly suitable for human walking analysis because it has a balanced feathers in upper side and lower side of body, in torso and extremities.

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