| dc.description.abstract | Postural control is a complex behavior that depends on the dynamic integration of visual, vestibular, and proprioceptive inputs, the allocation of attentional resources, and the coordination of neuromuscular responses. Postural control decline is a leading contributor to falls and a major cause of injury-related death and disability in aging and neurological populations. Despite this, postural control is still commonly assessed using subjective, performance-based clinical tools that measure only behavioral outcomes rather than the underlying mechanisms that produce them. The objective of this dissertation was to examine postural control across the lifespan and in neurological disorders, and to determine whether low-frequency oscillations in the center of pressure (COP) signal provide a more sensitive and mechanistic biomarker of fall risk than traditional measures alone.
This dissertation comprises four studies. The first was a systematic review and meta-analysis evaluating the diagnostic accuracy of the two most commonly used clinical fall-risk assessments among stroke survivors. Following PRISMA guidelines, 13 studies (1,347 stroke survivors) were analyzed. We found that the Berg Balance Scale (BBS; OR = 5.13, 95% CI [3.27, 8.05]) and the Timed Up and Go (TUG; OR = 3.38, 95% CI [2.23, 5.14]) demonstrated significant discriminative ability to categorize fall risk in stroke survivors, with no superiority of one over the other. However, moderate heterogeneity across studies and the absence of standardized cut-off values and assessment approaches indicated that neither tool is sufficient as a standalone screening measure.
The second and third studies were conducted in a sample of over 100 healthy younger and older adults. We examined how the underlying sensory reweighting mechanisms of postural control reorganize under dual-task conditions on a stable (Study 2) and an unstable (Study 3) surface. On both surfaces, older adults reduced postural sway under dual-task conditions but at the cost of cognitive accuracy, reflecting a reallocation of attentional resources toward postural control. Low-frequency oscillations of the COP signal revealed that sensory reweighting mechanisms were task- and direction-specific, and that age-associated differences became more pronounced on the unstable surface, where older adults relied more heavily on visual and vestibular inputs to compensate for challenged proprioception.
The fourth study examined whether fat mass index (FMI), fat-free mass index (FFMI), and the FM/FFM ratio predict COP sway and low-frequency oscillations in community-dwelling older and younger adults. We found that fat mass indices (FMI and the FM/FFM ratio) were significantly associated with postural sway and low-frequency oscillations exclusively in older adults, despite no significant differences in body composition between groups. Whereas FFMI showed no significant association in either group. This established adiposity as an independent, age-associated contributor to postural instability.
Collectively, this dissertation demonstrates that fall risk cannot be fully explained by behavioral outcomes alone. Across neurological disorders such as stroke, healthy aging, and body composition, low-frequency oscillations of the COP signal are able to capture the underlying sensory reweighting mechanisms of postural control. By distinguishing the quantity of postural sway from its quality, this work provides a mechanistic framework for understanding why individuals fall and supports the integration of objective, instrumented assessments into fall risk evaluation across aging and neurological populations. | en_US |
