QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

First published online July 31, 2009
Journal of Experimental Biology 212, 2668-2678 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.027581

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Adamczyk, P. G. Articles by Kuo, A. D. PubMed PubMed Citation Articles by Adamczyk, P. G. Articles by Kuo, A. D. Social Bookmarking                         What's this?

Redirection of center-of-mass velocity during the step-to-step transition of human walking

Peter G. Adamczyk^* and Arthur D. Kuo

Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109, USA

^* Author for correspondence (e-mail: padamczy{at}umich.edu)

Accepted 25 May 2009

Simple dynamic walking models based on the inverted pendulum predict that the human body's center of mass (COM) moves along an arc during each step, with substantial work performed to redirect the COM velocity in the step-to-step transition between arcs. But humans do not keep the stance leg perfectly straight and need not redirect their COM velocity precisely as predicted. We therefore tested a pendulum-based model against a wide range of human walking data. We examined COM velocity and work data from normal human subjects (N=10) walking at 24 combinations of speed (0.75 to 2.0 m s^–1) and step length. These were compared against model predictions for the angular redirection of COM velocity and the work performed on the COM during redirection. We found that the COM is redirected through angular changes increasing approximately linearly with step length (R²=0.68), with COM work increasing with the squared product of walking speed and step length (R²=0.82), roughly in accordance with a simple dynamic walking model. This model cannot, however, predict the duration of COM redirection, which we quantified with two empirical measures, one based on angular COM redirection and the other on work. Both indicate that the step-to-step transition begins before and ends after double support and lasts about twice as long – approximately 20–27% of a stride. Although a rigid leg model can predict trends in COM velocity and work, the non-rigid human leg performs the step-to-step transition over a duration considerably exceeding that of double support.

Key words: locomotion, biomechanics, center of mass, velocity, redirection, step-to-step transition, walking, work, inverted pendulum, leg compliance, hodograph, dynamic walking, step length

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    Twitter    What's this?