fourteen - Biomechanical constraints to stair negotiation

Summary

Introduction

The majority of falls in old age occur during stair descent (Svanstrom, 1974; Tinetti et al, 1988; Startzell et al, 2000; Hamel and Cavanagh, 2004). The physical injuries arising from such falls are of obvious concern, but of equal importance is the fear of falling, and loss of confidence and mobility. Therefore, it is imperative to establish effective measures to reduce the risk of stair falls and accidents, in order to maintain independence and quality of life in old age.

Stair ascent is challenging, and becomes increasingly difficult as people get older. However, paradoxically, it is during stair descent where problems are more common. This is because stepping down is a very complex task, for which the downward movement of the body has to be controlled and balance maintained each time the foot contacts the step (McFadyen and Winter, 1988; Riener et al, 2002). Our ability to do this depends on many factors, including muscle strength, joint mobility, proprioception, vision and balance ability, all of which deteriorate with age (for example, Evans and Campbell, 1993; Grimston et al, 1993; Maki and McIlroy, 1996; Reeves et al, 2006).

Two critical design characteristics in a staircase that are related to these functional parameters are the step-rise, which is the height of each step, and the step-going, the depth of the step. It is possible that older individuals may be less able to generate the muscle forces required to support the body on the upper step or to control the motion when landing on the lower step. In fact, we have already documented that older people use more of their available muscle strength in their knee extensors and ankle plantarflexors to ascend and descend a staircase than younger people (Reeves et al, 2008, 2009). Previously, we examined stair negotiation of standard step dimensions (going: 280 mm, rise: 170 mm) with older adults. However, it is likely that age-related differences are amplified, with greater strength reserves required for more demanding stair-negotiating tasks (particularly higher step-rise) for the old. On the other hand, if the step-going is small (as is often the case in older homes), the ball of the foot of the lead leg will be placed towards the front edge of the step during descent, risking a slip.