The Sensorimotor Locus of Balance Control in Elderly Gait

Study Overview
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Brief Summary
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The aging population is at an exceptionally high risk of debilitating falls, contributing significantly to reduced independence and quality of life. It remains extremely challenging to screen for falls risk, and programs designed to mitigate falls risk have only modestly influenced the sizeable portion of the aging population experiencing one or more falls annually. Balance control in standing and walking depends on integrating reliable sensory feedback and on planning and executing appropriate motor responses. Walking balance control is especially dynamic, requiring active and coordinated adjustments in posture (i.e., trunk stabilization) and foot placement from step to step. Accordingly, using a custom, immersive virtual environment, the investigators have shown that sensory (i.e., optical flow) perturbations, especially when applied during walking, elicit strong and persistent motor responses to preserve balance. Exciting pilot data suggest that these motor responses are remarkably more prevalent in old age, presumably governed by an increased reliance on vision for balance control. Additional pilot data suggest that prolonged exposure to these perturbations may effectively condition successful balance control strategies. Founded on these recent discoveries, and leveraging the increase reliance on vision for balance control in old age, the investigators stand at the forefront of a potentially transformative new approach for more effectively identifying and mitigating age-related falls risk. The investigator's overarching hypothesis is that optical flow perturbations, particularly when applied during walking, can effectively identify balance deficits due to aging and falls history and can subsequently condition the neuromechanics of successful balance control via training.

Detailed Description
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Specific Aim 1. Investigate sensory, motor, and cognitive-motor mechanisms governing susceptibility to optical flow perturbations. Aging increases the reliance on vision for balance control. However, central and peripheral mechanisms underlying aging and falls history effects on the susceptibility to optical flow perturbations are unclear. Hypothesis 1: Entrainment to optical flow perturbations will correlate most strongly with visual dependence and decreased somatosensory function, alluding to an age-associated process of multi-sensory reweighting. Methods: Multivariate models will quantify the extent to which strategically-selected sensory (i.e., visual dependence via rod/frame test, somatosensory function), motor (i.e., rate of torque development, timed sit-to-stand) and cognitive-motor (i.e., interference) mechanisms underlie inter-individual differences in susceptibility to perturbations. Specific Aim 2. Estimate the efficacy of prolonged optical flow perturbations to condition the neuromechanics of walking balance control in older adult fallers. Pilot data from young adults suggests that prolonged exposure to optical flow perturbations may condition reactive strategies used to successfully control walking balance. The investigator's premise is that dynamic perturbation training can improve resilience to unexpected balance disturbances. Here, the investigators conduct a preliminary test of the effects of training with optical flow perturbations on walking balance in older adult fallers. Hypothesis 2: (a) Older adults with a history of falls will adapt to prolonged exposure to perturbations, conditioning their step to step adjustments in walking balance control, and (b) improving their response to unexpected balance challenges following training. Methods: In two 20 min sessions, on different days in a randomized cross-over design, older adults with a history of falls will walk with (treatment session) and without (control session) prolonged exposure to optical flow perturbations. The investigators will assess time-dependent changes in the neuromechanics of walking balance during training and after-effects via gait variability, dynamic stability, and performance on a series of real-world like targeting and obstacle avoidance tasks.

Official Title
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The Sensorimotor Locus of Balance Control in Elderly Gait

Conditions
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Ambulation Difficulty, Gait, Unsteady, Fall, Position Sense Disorders

Intervention / Treatment
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* Behavioral: Optical flow perturbations
* Behavioral: Normal walking


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Be able to walk without an assistive aid (i.e., walker, cane) Have the full capacity to provide informed consent OLDER NON-FALLERS Age 65+ years No history of falls* in the prior 12 months OLDER ADULTS WITH A HISTORY OF FALLS Age 65+ years History of one or more falls* in the prior 12 months For the purposes of this study, falls counted towards the self-reported total will be defined as per the Kellogg International Work Group - a fall is unintentionally coming to the ground or some lower level and other than as a consequence of sustaining a violent blow, loss of consciousness, sudden onset of paralysis as in stroke or an epileptic seizure Exclusion Criteria: Current lower extremity injury or fracture Taking medication that causes dizziness Have a leg prosthesis Prisoners Individuals clearly lacking the capacity to provide informed consent

Ages Eligible for Study
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Minimum Age: 65 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Treatment
Allocation: Randomized
Intervention Model: Crossover Assignment
Interventional Model Description: In two 20 min sessions, on different days in a randomized cross-over design, older adults will walk with (treatment session) and without (control session) prolonged exposure to optical flow perturbations.
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Intervention, then Control<br>Older adults will walk during exposure to optical flow perturbations | Behavioral: Optical flow perturbations<br>* Continuous mediolateral (i.e., side-to-side) 20-minute perturbations of optical flow that elicit the visual perception of lateral imbalance via virtual reality during treadmill walking.<br>Behavioral: Normal walking<br>* Usual treadmill walking without optical flow perturbations<br>|
| Experimental: Control, then Intervention<br>Older adults will walk normally (without optical flow perturbations) | Behavioral: Optical flow perturbations<br>* Continuous mediolateral (i.e., side-to-side) 20-minute perturbations of optical flow that elicit the visual perception of lateral imbalance via virtual reality during treadmill walking.<br>Behavioral: Normal walking<br>* Usual treadmill walking without optical flow perturbations<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Change in Postural Sway After 10 Min of Walking | Magnitude of side-to-side postural sway | Baseline, 10 minutes | 
| Change in Kinematic Variability After 10 Min of Walking | Magnitude of step-to-step corrections in step width measured in cm | Baseline, 10 minutes | 
| Change in Foot Placement Targeting Accuracy After 10 Min of Walking | Accuracy of performing foot placement targeting task. i.e., distance between heel marker at initial contact and target line (measured using three-dimensional motion capture during walking). | Baseline, 10 minutes | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Change in Cognitive-motor Interference Accuracy After 10 Min of Walking | Accuracy performing an auditory stroop test (cognitive dual-task) | Baseline, 10 minutes | 
| Change in Cognitive-motor Interference Response Time After 10 Min of Walking | Response time in performing an auditory stroop test (cognitive dual-task) | Baseline, 10 minutes | 
| Change in Margin of Stability Variability After 10 Min of Walking | Change in step-to-step fluctuations in margin of stability (the distance between the lateral boundary of the foot and the body's center of mass, measured in cm) | Baseline, 10 minutes |