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Gait & Posture 29 (2009) 326–331

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Dimensional analysis and ground reaction forces for stair climbing: Effects of age and task difficulty
Matteo Bertucco a,b, Paola Cesari a,b,*
a b

Department of Neurological and Visual Sciences, University of Verona, Italy Faculty of Exerciseand Sport Sciences, University of Verona, Italy



Article history: Received 11 April 2008 Received in revised form 1 October 2008 Accepted 2 October 2008 Keywords: Stair climbing Elderly Perception–action coupling Self-efficacy

Altered perception–action capability is often associated with falls and diminished self-efficacy in older people. This studyevaluated and compared perception–action capability in stair-climbing performance of 18 healthy volunteers assigned to two age groups (mean age, 26.3 Æ 4.3 years and 66.4 Æ 4.7 years, respectively). The experimental set-up included 14 stairs (50 cm wide, 60 cm deep, riser height 35–90 cm) positioned at the edge of a force platform. The task was to climb the stair with the greatest riser heightsubjects thought they could climb without outside support or use of hands. Dimensional and dynamic data were collected and analyzed to reveal the invariant relationships that sustain action preparation and execution. All subjects chose the same proportion between stair height and distance covered before mounting the stair, as expressed by the invariant angle (a). While the geometric invariantrelationship was picked up as a visual guide prior to action, there was a dynamic invariance in the forces applied during actual execution. To establish whether the invariance still held in extreme cases, two perturbed conditions were introduced in which stair distances were changed, forcing subjects to execute a foot-strike, either very far from or near to the stair, before climbing it, so as to revealany significant adaptations the climber would undertake to avoid slips or falls. Older and younger subjects applied appropriate visual and motor guidance by scaling their motor capabilities to the environmental dimensions. ß 2008 Elsevier B.V. All rights reserved.

1. Introduction Falls are the number one cause of fractures, hospital admissions for trauma, loss of independence, and death due toinjury in older adults [1,2]. Whether caused by perceptual or motor impairment [3], falls are often associated with alterations in a person’s perception–action capability (i.e., an individual’s ability to judge and perform a motor task) and self-efficacy. Increasingly considered as a key factor in fall prevention in the elderly [4–6], selfefficacy refers to a person’s perception of his/her ability tomove and to accomplish a goal. In general, it is a belief (whether or not accurate) that one has in his/her capacity to obtain a successful performance. This latter concept has clinical relevance for health promotion, especially in relation to functional decline in the elderly population [7–9]. A powerful approach to this problem is to investigate actor self-evaluation and assess his/her actualperformance on such motor tasks as stair climbing.

* Corresponding author at: Department of Neurological and Visual Sciences, Faculty of Exercise and Sport Sciences, University of Verona–Italy, Via Casorati 43, 37131 Verona, Italy. Tel.: +39 045 8425124; fax: +39 045 8425131. E-mail address: (P. Cesari). 0966-6362/$ – see front matter ß 2008 Elsevier B.V. All rights reserved.doi:10.1016/j.gaitpost.2008.10.052

Studies employing tasks that ask people to select and then climb stairs with the maximum riser height they considered climbable without the aid of the hands [10–17] have shown that, in children, young people, and the elderly, self-assessment and actual performance can be predicted from an invariant relationship consisting of the angle (a) defined by the...
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