Stroke is a leading cause of disability in the United States, affecting approximately 795,000 people annually. The Veteran's Health Administration provides over 60,000 outpatient visits for stroke-related care annually at a cost of over $250 million. Among ambulatory people with chronic stroke (PwCS), impaired balance is a common health concern that substantially limits mobility (those with the worst balance walk the least). This project will explore adaptive strategies employed by PwCS in balance challenging environments and if a novel gait training intervention using a robotic device to amplify a person's self-generated movements can improve walking balance. The development of effective interventions to increase walking balance among PwCS will positively impact Veterans' health, quality of life, and ability to participate in walking activities.

Background: There is a pressing need to develop effective methods to enhance walking balance in people with chronic stroke (PwCS). Interventions that amplify self-generated movements may accelerate motor learning by enhancing a person's perception of movement errors. This method could potentially be applied to help PwCS improve walking balance. To this end, the investigators have developed a cable-driven robot to create a Movement Amplification Environment (MAE) during treadmill walking. The MAE challenges walking balance by applying lateral forces to the pelvis that are proportional in magnitude to real-time lateral center of mass (COM) velocity.

Unlike a popular form of balance training that uses unpredictable perturbations to enhance reactive balance, training in a MAE targets anticipatory balance by developing predictive control mechanisms that are likely to persist when the training environment is removed (after-effects). The investigators believe that supplementing high-intensity gait training (the recommended practice to improve walking speed and distance) with a MAE will substantially enhance walking balance. Thus, the purpose is to evaluate the unique effects of MAE training on walking balance in PwCS and determine feasibility of conducting high-intensity gait training in a MAE.

Specific Aims: Aim 1: To evaluate gait patterns PwCS adapt during and immediately following walking practiced in two balance-challenging training environments: MAE and unpredictable lateral perturbations. Aim 2: To establish feasibility of high intensity gait training in MAE the investigators will evaluate cardiovascular intensity during gait training interventions performed in either a natural unmodified environment or a MAE.

Approach: Aims 1: 15 PwCS will participate in a single-day experiment evaluating gait biomechanics (COM dynamics and stepping patterns) during and immediately following treadmill walking performed in a MAE or while receiving frequent unpredictable lateral perturbations. Outcomes will assess if changes in gait patterns to maintain stability persist immediately following exposure to either of the balance-challenging environments. Aim 2: 15 PwCS will participate in two high-intensity gait training sessions. One session will be performed in a natural unmodified environment, the other in a MAE. The investigators will quantify differences in mean heart rate (HR) between the two sessions and whether mean HR is in the target high-intensity range of 70-85% of maximum HR.

Impact: This project will identify if and how PwCS uniquely adapt locomotor strategies following exposure to balance challenging environments and evaluate feasibility of administering high-intensity gait training in a MAE. Training walking balance of PwCS in a MAE by amplifying their own self-generated movements is a radical departure from current practice and could substantially enhance walking balance. Successful outcomes will motivate a future randomized controlled trial assessing the efficacy of MAE training to enhance walking balance in PwCS.

Inclusion Criteria:

• History of chronic stroke (more than 6 months post-stroke) with weakness on one side
• Ability to ambulate over ground for 10 meters with or without a single cane, and/or ankle-foot orthosis
• Ability to tolerate 10 minutes of standing

Exclusion Criteria:

• Presence of cognitive impairment (score of 22/30 on the Montreal Cognitive Assessment scale (MoCA))
• Presence of aphasia (score of 71/100 on the Mississippi Aphasia Screening Test (MAST))
• Excessive spasticity in lower limbs (score of > 3 on the Modified Ashworth Scale
• Severe cardiovascular and pulmonary disease affecting gait and balance
• History of recurrent fractures or known orthopedic problems in the lower extremities (i.e. heterotopic ossification) affecting gait and balance
• Concomitant central or peripheral neurological injury (i.e. traumatic head injury or peripheral nerve damage in lower limbs) affecting gait and balance
• Evidence of cerebellar ataxia
• Presence of unhealed decubiti or other skin compromise
• Enrollment in concurrent physical therapy or research involving gait or balance training
• Use of braces/orthotics crossing the knee joint
• Known pregnancy

The investigators will create and share de-identified, anonymized data sets. Data sets will be open file formats that include documentation of the material. The investigators will link data sets to associated study publications. Final data sets will be made available as per Hines VA Hospital local policy for long term storage and access until enterprise-level resources become available. These data will be available upon request by researchers and scientists in accordance with federal guidelines and Hines local policy.

The final data sets will be sufficient for anyone to perform analogous or supplemental analyses that would permit validation of the analysis and results.

Data will be available following the completion and publication of study results.

Data will be publicly available.