The distance of visual targets affects the spatial magnitude and multifractal scaling of standing body sway in younger and older adults

Abstract

The spatial magnitude of standing body sway is greater during viewing of more distant targets and reduced when viewing nearby targets. Classical interpretations of this effect are based on the projective geometry of changes in visual stimulation that are brought about by body sway. Such explanations do not motivate predictions about the temporal dynamics of body sway. We asked whether the distance of visible targets would affect both the spatial magnitude and the multifractality of standing body sway. It has been suggested that the multifractality of movement may change with age. Separately, previous research has not addressed the effects of target distance on postural sway in older adults. For these reasons, we crossed our variation in target distance with variation in age. In an open-air setting, we measured standing body sway in younger and older adults while looking at visual targets that were placed at three distances. The distance of visual targets affected the spatial magnitude of body sway in younger adults, replicating past studies. Target distance also affected the spatial magnitude of sway in older adults, confirming that this relation persists despite other age-related changes. Target distance also affected the multifractality of body sway, but this effect was modulated by age. Finally, the width of the multifractal spectrum was greater for older adults than for younger adults, revealing that healthy aging can affect the multifractality of movement. These findings reveal similarities and differences between the spatial magnitude and the multifractality of human movement.

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

“…Yet the same researchers have acknowledged that, due to its novelty, the interpretation of data on multifractality often is not straightforward. In the present study, our use of and predictions about MF-DFA were based on published derivations of the analytic technique, and on published empirical studies showing that MF-DFA can be influenced by a variety of behaviorally relevant independent variables [25, 32–34, 37]. …”

“…The logical limit of this relationship occurs when people look at the horizon. On land, the spatial magnitude of postural sway is greater when looking at the visible horizon than when looking at nearby targets, in both younger and older adults [11, 16, 25]. Typically, these effects are stronger for postural sway in the body’s anterior-posterior (AP) axis than for sway in the body’s mediolateral (ML) axis.…”

“…Ihlen et al [32] and Goldberger et al [38] suggested that age-related changes in physiology and neurology might lead to a reduction in the multifractality of movement. Munafo et al [25] compared the multifractality of standing sway in younger and older healthy adults. They confirmed the existence of an age effect; however, the degree of multifractality was greater in older adults than in younger adults, directly contrary to the prediction of Goldberger et al…”

“…Munafo et al [25] also investigated the influence of the horizon on postural sway in younger and older adults. In addition to evaluating the spatial magnitude of postural sway, they separately evaluated the multifractality of sway.…”

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

“…A recent study [8] reported that the spatial magnitude of sway is affected by the gaze target distance in older adults, also showing that the width of the multifractal spectrum (a measure of temporal dynamics) is greater for older adults when compared with younger adults. Accordingly, Mufano, Wade, Stergiou and Stoffregenet [13] evaluated the kinematics of the CoP, regarding the amount of sway and the multifractality, in elderly people standing on a ship at sea (that departed from Nassau, Bahamas) when looking to the nautical horizon. Two premises were asked: (1) the spatial amplitude of postural sway could decrease when looking at the nautical horizon comparing to a closer target; (2) the nautical horizon could affect the multifractality of standing body sway in older adults.…”