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Age Group Differences in Postural Adjustments Associated With a Stepping Task.

V S Mercer·S A Sahrmann·V Diggles-Buckles·R A Abrams·B J Norton
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Abstract

In this study, differences among age groups in the postural adjustments associated with a stepping task were identified. Twenty subjects from each of 3 age groups, children (8-12 years), young adults (25-35 years), and older adults (65-73 years), performed the task in 2 movement contexts: place and step. In place, the subject simply lifted the foot and placed it on the step. In step, the subject lifted the foot, placed it on the step, and stepped up onto the step. Latencies of postural and focal muscle activation were determined by using surface electromyography and pressure switches. Center of pressure (CP) data were obtained by using a force platform. Subjects in all 3 age groups consistently demonstrated postural adjustments before movement initiation. Children displayed longer postural latencies than young adults as well as disproportionately large values for CP path length. Older adults showed prolonged postural-focal latencies and decreased CP excursions compared with the 2 younger age groups. These results suggest that maturation of coordination between posture and movement may not be fully complete in 8- to 12-year-olds and that increased restraint characterizes the performance of postural adjustments in healthy persons over 65 years of age.

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center of pressurehuman stancepostural adjustmentreaction timesteppingJournal Article

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BibTeXRIS

V S Mercer, S A Sahrmann, V Diggles-Buckles, R A Abrams, B J Norton. 1997. Age Group Differences in Postural Adjustments Associated With a Stepping Task.. https://doi.org/10.1080/00222899709600839

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Virtual Time-to-Collision and Human Postural Control.

This article is a report on 3 experiments designed so that the role of virtual time-to-collision (VTC), which specifies the spatiotemporal proximity of the center of pressure to the postural stability boundary in the regulation of posture in upright stances, could be examined. Virtual time-to-collision was estimated for normal upright stance with different bases of support, and for postural oscillations in which the speed of movement and instructional constraints on the coordination mode used were manipulated. The results showed that virtual time-to-collision was predictably reduced as (a) the base of support was reduced, (b) the speed of the postural oscillation was increased, and (c) the number of biomechanical degrees of freedom regulated in the coordination mode increased. Over a range of task conditions, the coefficients of variation of the VTC time-series were significantly lower than the coefficients of variation for the velocity and acceleration time-series of the center of pressure. The absolute values of VTC increased with the increment of the ground reaction forces a performer generated to avoid falling while approaching the stability boundary. These findings are consistent with the proposition that VTC may serve as an organizing informational control parameter for posture.

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