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The Journals of Gerontology Series A: Biological Sciences and Medical Sciences Advance Access originally published online on April 7, 2009
The Journals of Gerontology Series A: Biological Sciences and Medical Sciences 2009 64A(7):807-815; doi:10.1093/gerona/glp027
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© 2009 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Impaired Reactive Stepping Adjustments in Older Adults

Shih-Chiao Tseng1,2, Steven J. Stanhope3,4 and Susanne M. Morton1,2,5

1 Department of Physical Therapy & Rehabilitation Science, University of Maryland School of Medicine, Baltimore
2 Graduate Program in Physical Therapy & Rehabilitation Science, University of Iowa Carver College of Medicine, Iowa City
3 Department of Health, Nutrition & Exercise Sciences
4 Department of Mechanical Engineering, University of Delaware, Newark
5 Department of Anatomy & Neurobiology, University of Maryland School of Medicine, Baltimore

Address correspondence to Susanne M. Morton, PT, PhD, Graduate Program in Physical Therapy & Rehabilitation Science, University of Iowa Carver College of Medicine, 1-252 Medical Education Building, Iowa City, IA 52242. Email: susanne-morton{at}uiowa.edu


  Abstract

Background: The ability to redirect the path of the foot during walking is critical for responding to perturbations and maintaining upright stability. The purpose of the current study was to compare mechanisms of reactive stepping adjustments in young versus older adults when responding to an unexpected perturbation during voluntary step initiation.

Methods: We tested 13 healthy community-dwelling older adults and an equal number of young control participants performing stepping movements onto a visual target on the floor. In some trials, perturbations were introduced by unexpectedly shifting the target, at various time points, from its usual location to a new location 20 cm to the right. We measured ground reaction forces under the supporting leg and three-dimensional kinematics of the stepping leg in baseline and target shift trials.

Results: During target shift trials, that is, when reactive adjustments were required, older adults demonstrated the following: delayed responses in modifying the lateral propulsive forces under the supporting foot, reduced rates of lateral force production, delayed responses in modifying the stepping foot trajectory, and prolonged movement execution times.

Conclusions: The current study quantitatively distinguishes between healthy older and young adults in generating reactive stepping adjustments to an unpredictable shift of a visual target. The decreased capability for rapidly planning and executing an effective voluntary step modification could reveal one potential cause for the increased risk of falls in the older population.

Keywords Aging; Postural control; Falls; Biomechanics; Gait

Received: February 18, 2008; Accepted: January 23, 2009

Decision Editor: Luigi Ferrucci, MD, PhD


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