Exploring the Role of Centre of Mass Variability in Reactive Balance Control

Increased variability of movement is related to increased risk for falls. The objective of the current work was to better understand the role of variability in balance control. It was hypothesized that high centre of mass (COM) variability (position and velocity) while standing would induce a stepping response after a balance perturbation compared to low COM variability. It was also hypothesized that a low margin of stability (MOS) at perturbation onset would induce stepping response after a platform perturbation. Fourteen young adults (20-35 years old) were recruited. Participants experienced postural perturbations when standing using surface translations. COM variability and MOS did not differ between stepping and feet in place responses. The current results suggest that transient changes in movement variability may not influence reactive balance control. Instead, increased movement variability may be a sign of aging or motor impairment.M.Sc

Exploring the Role of Centre of Mass Variability in Reactive Balance Control

Increased variability of movement is related to increased risk for falls. The objective of the current work was to better understand the role of variability in balance control. It was hypothesized that high centre of mass (COM) variability (position and velocity) while standing would induce a stepping response after a balance perturbation compared to low COM variability. It was also hypothesized that a low margin of stability (MOS) at perturbation onset would induce stepping response after a platform perturbation. Fourteen young adults (20-35 years old) were recruited. Participants experienced postural perturbations when standing using surface translations. COM variability and MOS did not differ between stepping and feet in place responses. The current results suggest that transient changes in movement variability may not influence reactive balance control. Instead, increased movement variability may be a sign of aging or motor impairment.M.Sc

Exploring the relationship between stability and variability of the centre of mass and centre of pressure

There are competing perspectives in the literature regarding the role of movement variability in quiet standing and balance control. Some view high variability as indicative of poor balance control and a contributor to increased fall risk, whereas others view variability as beneficial in providing sensory information that aids balance control

Characterizing slip-like responses during gait using an entire support surface perturbation: Comparisons to previously established slip methods

The characteristics of experimentally induced slips (low-friction surfaces and non-motorized platforms) in laboratory settings are influenced by participant gait velocity, contact surface area, and level of friction between the foot and surface. However, motorized platforms that could account for these factors during slip-like paradigms have not been extensively used.This work was supported by the Natural Sciences and Engineering Research council of Canada (RGPIN-2014-04199) and the Ministry of Research and Innovation. We acknowledge the support of the Toronto Rehabilitation Institute; equipment and space have been funded with grants from the Canada Foundation for Innovation, Ontario Innovation Trust, and the Ministry of Research and Innovation. AHH was supported by a Trainee Award from the Heart and Stroke Foundation Canadian Partnership for Stroke Recovery. RR was supported by awards from the Toronto Rehabilitation Institute and the Unilever/Lipton Graduate Fellowship in Neuroscience. ASI was supported by a Trainee Award from the Heart and Stroke Foundation Canadian Partnership for Stroke Recovery and an Interdisciplinary Fellowship from the Canadian Frailty Network during this work. AM holds a New Investigator Award from the Canadian Institutes of Health Research (MSH 141983)

Is perception of vertical impaired in individuals with chronic stroke with a history of ‘pushing’?

AbstractPost-stroke ‘pushing’ behaviour appears to be caused by impaired perception of vertical in the roll plane. While pushing behaviour typically resolves with stroke recovery, it is not known if misperception of vertical persists. The purpose of this study was to determine if perception of vertical is impaired amongst stroke survivors with a history of pushing behaviour. Fourteen individuals with chronic stroke (7 with history of pushing) and 10 age-matched healthy controls participated. Participants sat upright on a chair surrounded by a curved projection screen in a laboratory mounted on a motion base. Subjective visual vertical (SVV) was assessed using a 30 trial, forced-choice protocol. For each trial participants viewed a line projected on the screen and indicated if the line was tilted to the right or the left. For the subjective postural vertical (SPV), participants wore a blindfold and the motion base was tilted to the left or right by 10–20°. Participants were asked to adjust the angular movements of the motion base until they felt upright. SPV was not different between groups. SVV was significantly more biased towards the contralesional side for participants with history of pushing (−3.6±4.1°) than those without (−0.1±1.4°). Two individuals with history of pushing had SVV or SPV outside the maximum for healthy controls. Impaired vertical perception may persist in some individuals with prior post-stroke pushing, despite resolution of pushing behaviours, which could have consequences for functional mobility and falls

Atypical anticipatory postural adjustments during gait initiation among individuals with sub-acute stroke

Anticipatory postural adjustments, executed prior to gait initiation, help preserve lateral stability when stepping. Atypical patterns of anticipatory activity prior to gait initiation may occur in individuals with unilateral impairment (e.g., stroke). This study aimed to determine the prevalence, correlates, and consequences of atypical anticipatory postural adjustment patterns prior to gait initiation in a sub-acute stroke population. Forty independently-ambulatory individuals with sub-acute stroke stood on two force plates and initiated gait at a self-selected speed. Medio-lateral centre of pressure displacement was calculated and used to define anticipatory postural adjustments (shift in medio-lateral centre of pressure >10 mm from baseline). Stroke severity, motor recovery, and functional balance and mobility status were also obtained. Three patterns were identified: single (typical), absent (atypical), and multiple (atypical) anticipatory postural adjustments. Thirty-five percent of trials had atypical anticipatory postural adjustments (absent and multiple). Frequency of absent anticipatory postural adjustments was negatively correlated with walking speed. Multiple anticipatory postural adjustments were more prevalent when leading with the non-paretic than the paretic limb. Trials with multiple anticipatory postural adjustments had longer duration of anticipatory postural adjustment and time to foot-off, and shorter unloading time than trials with single anticipatory postural adjustments. A high prevalence of atypical anticipatory control prior to gait initiation was found in individuals with stroke. Temporal differences were identified with multiple anticipatory postural adjustments, indicating altered gait initiation. These findings provide insight into postural control during gait initiation in individuals with sub-acute stroke, and may inform interventions to improve ambulation in this population