The Sensorimotor Locus of Balance Control in Elderly Gait

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.

Study Overview

• Status: Completed
• Conditions: Fall; Gait, Unsteady; Ambulation Difficulty; Position Sense Disorders
• Intervention / Treatment: Behavioral: Optical flow perturbations; Behavioral: Normal walking

Detailed Description

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.

• Study Type: Interventional
• Enrollment (Actual): 14
• Phase: Not Applicable

Contacts and Locations

Study Locations

• United States
  • North Carolina
    • Chapel Hill, North Carolina, United States, 27514
      • Applied Biomechanics Laboratory

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 65 years and older (OLDER_ADULT)
• Accepts Healthy Volunteers: Yes
• Genders Eligible for Study: All

Description

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

Study Plan

How is the study designed?

Design Details

• Primary Purpose: TREATMENT
• Allocation: RANDOMIZED
• Interventional Model: CROSSOVER
• Masking: NONE

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
EXPERIMENTAL: Intervention, then Control; Older adults will walk during exposure to optical flow perturbations	Behavioral: Optical flow perturbations; 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.; Behavioral: Normal walking; Usual treadmill walking without optical flow perturbations
EXPERIMENTAL: Control, then Intervention; Older adults will walk normally (without optical flow perturbations)	Behavioral: Optical flow perturbations; 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.; Behavioral: Normal walking; Usual treadmill walking without optical flow perturbations

What is the study measuring?

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

Collaborators and Investigators

• Sponsor: University of North Carolina, Chapel Hill
• Collaborators: National Institute on Aging (NIA)
• Investigators: Principal Investigator: Jason Franz, PhD, Unviersity of North Carolina at Chapel Hill

Publications and helpful links

General Publications

• Franz JR, Francis CA, Allen MS, O'Connor SM, Thelen DG. Advanced age brings a greater reliance on visual feedback to maintain balance during walking. Hum Mov Sci. 2015 Apr;40:381-92. doi: 10.1016/j.humov.2015.01.012. Epub 2015 Feb 14.
• Francis CA, Franz JR, O'Connor SM, Thelen DG. Gait variability in healthy old adults is more affected by a visual perturbation than by a cognitive or narrow step placement demand. Gait Posture. 2015 Sep;42(3):380-5. doi: 10.1016/j.gaitpost.2015.07.006. Epub 2015 Jul 17.
• Thompson JD, Franz JR. Do kinematic metrics of walking balance adapt to perturbed optical flow? Hum Mov Sci. 2017 Aug;54:34-40. doi: 10.1016/j.humov.2017.03.004. Epub 2017 Apr 2.
• Stokes HE, Thompson JD, Franz JR. The Neuromuscular Origins of Kinematic Variability during Perturbed Walking. Sci Rep. 2017 Apr 11;7(1):808. doi: 10.1038/s41598-017-00942-x.
• Richards JT, Selgrade BP, Qiao M, Plummer P, Wikstrom EA, Franz JR. Time-dependent tuning of balance control and aftereffects following optical flow perturbation training in older adults. J Neuroeng Rehabil. 2019 Jul 1;16(1):81. doi: 10.1186/s12984-019-0555-3.

Helpful Links

• Applied Biomechanics Laboratory

Study record dates

Study Major Dates

• Study Start (ACTUAL): October 30, 2017
• Primary Completion (ACTUAL): July 25, 2018
• Study Completion (ACTUAL): July 25, 2018

Study Registration Dates

• First Submitted: October 31, 2017
• First Submitted That Met QC Criteria: November 13, 2017
• First Posted (ACTUAL): November 14, 2017

Study Record Updates

• Last Update Posted (ACTUAL): July 5, 2019
• Last Update Submitted That Met QC Criteria: June 27, 2019
• Last Verified: February 1, 2019

More Information

Terms related to this study

• Additional Relevant MeSH Terms: Nervous System Diseases; Neurologic Manifestations; Sensation Disorders; Gait Disorders, Neurologic; Mobility Limitation; Somatosensory Disorders
• Other Study ID Numbers: 15-2267; R56AG054797-01A1 (NIH)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: There is no plan to share IPD with other researchers.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No