The Rim and the Ancient Mariner: The Nautical Horizon Affects Postural Sway in Older Adults

Abstract

On land, the spatial magnitude of postural sway (i.e., the amount of sway) tends to be greater when participants look at the horizon than when they look at nearby targets. By contrast, on ships at sea, the spatial magnitude of postural sway in young adults has been greater when looking at nearby targets and less when looking at the horizon. Healthy aging is associated with changes in the movement patterns of the standing body sway, and these changes typically are interpreted in terms of age-related declines in the ability to control posture. To further elucidate the mechanisms associated with these changes we investigated control of posture in a setting that poses substantial postural challenges; standing on a ship at sea. In particular, we explored postural sway on a ship at sea when older adults looked at the horizon or at nearby targets. We evaluated the kinematics of the center of pressure in terms of spatial magnitude (i.e., the amount of sway) and multifractality (a measure of temporal dynamics). We found that looking at the horizon significantly affected the multifractality of standing body, but did not systematically influence the spatial magnitude of sway. We discuss the results in terms of age-related changes in the perception and control of dynamic body orientation.

The “Journal of Functional Morphology and Kinesiology” Journal Club Series: Highlights on Recent Papers in Movement Analysis

“…These findings showed that the nautical horizon has an influence on the multifractality of sway, increasing spectrum width when regarding a closer target. These results are different from those observed on land where a decreased spectrum width is observed for a more distant visual targets compared to closer ones [14]. The ship motion is seen as a form of motor constraint that can eliminate age related-variations in the spatial magnitude of postural sway.…”

Multifractal evidence of nonlinear interactions stabilizing posture for phasmids in windy conditions: A reanalysis of insect postural-sway data

“…As for the first goal, the multifractal-spectrum width W should likely exhibit the same pattern that as variability measures for postural sway did in the original report on these data: an initial increase due to wind stimulation and a smooth decrease as the phasmids acclimate to the wind stimulation. Indeed, prior work examining posture has shown that greater sway corresponds to greater multifractality [ 3 , 4 ]. It may hopefully only serve to confirm the intuitive similarities between multifractal spectrum width w and SD .…”