Finite collision model for the double support phase of human walking

Abstract

In this research, the human walking is modeled as a simple mechanical system and used for analyzing energetic feature of gait. Among many previously suggested walking models, the inverted pendulum-like model is mostly accepted one. The model proposed by Garcia and supported by Kuo is the simplest type of inverted pendulum model. Though it is very simple mechanical model, it could predict the energetic features of human gait such as mechanical work done on the center-of-mass or mechanical power of each joint using gait parameters such as step length and step frequency. However, the model also has a defect due to excessive simplification, especially on the double support phase where the center-of-mass velocity redirection occurs. The model assumes that the momentum changing process occurs instantaneously by simultaneous push-off and heel-strike impulses. In fact, it is not an instantaneous process but occur over finite time duration. Therefore, the simplest walking model could not explain some mechanical features related to the momentum changing process. Based on the existing simplest walking model, the model suggested in this research reflects finite time duration of momentum changing process. Thus, the gravitational effect on the center-of-mass during the process, which was ignored in the existing model, is included. To verify the model, human walking experiment was performed and 6 subjects have participated. Subjects have walked following the 5 different frequency cues and ground reaction forces and kinematic information have measured. The result showed that the model could explain the gait features that were not possible to be explained by the existing model. The gait strategy change from ankle to hip with increasing walking speed was observed. This is due to the biomechanical constraint of the ankle, and is explained by making proper assumption to the suggested model``s prediction.