People post-stroke retain the capacity to modify walking patterns explicitly using biofeedback and implicitly when encountering changes in the walking environment. This proposal will assess changes in muscle activation patterns associated with walking modifications driven explicitly vs. implicitly, to determine whether individuals generate different amounts of co-contraction during explicit vs. implicit walking modifications. Understanding how walking modifications driven explicitly vs. implicitly influence co-contraction will allow the investigators to identify approaches that can more effectively restore muscle activation toward pre-stroke patterns, promoting mechanism-based recovery of walking function.

This proposal aims to determine the effects of explicitly driven or implicitly driven walking modifications on muscle activation patterns and co-contraction post-stroke. This work is significant, as studies have shown that muscle activation patterns after neurologic injury cannot generate walking kinematics comparable to those seen in neurotypical individuals; this finding implies that to attain true walking recovery after neurologic injury, interventions should aim to restore the muscle activations underlying walking behaviors. Here, the researchers first explore muscle activations during walking using biofeedback to guide explicit modification of walking patterns, which is a common approach used in clinical and research interventions for walking retraining. The hypothesis is that explicit walking modifications might be detrimental at a muscle activation level as they engage cortical pathways for voluntary control that have been interrupted by the stroke lesion, resulting in increased muscle co-contraction. Co-contraction hinders true recovery as it impairs the ability to selectively control different segments during walking, resulting in overreliance on compensatory patterns. Researchers will also explore muscle activation patterns during implicit walking modifications. Researchers will use external modifications in the walking environment, mainly split-belt adaptation followed by tied belt walking, to assess if implicit modifications of walking that rely less on cortical neural control are associated with levels of cocontraction comparable to neurotypical controls-an indication that implicitly-mediated modifications could be a more effective approach to restore muscle activation patterns during walking post-stroke. In this study, researchers will assess co-contraction during walking in people post-stroke as the patient reduces asymmetry in step lengths guided by explicit biofeedback (Aim 1) or implicitly following split-belt adaptation and washout (Aim 2). Results from this study will identify the tasks and conditions that can reduce cocontraction to promote restoration of neuromuscular control post-stroke. This proposal will aid develop objective markers of treatment response and functional progress that predict rehabilitation treatment response and enable the tailoring of interventions to the needs, abilities, and resources of the person with disability.

Inclusion Criteria for stroke survivors are:

• Chronic hemiparesis (time since stroke > 6 months) caused by a single documented stroke event.
• Ability to walk on the treadmill continuously for 2 minutes
• Ability to walk over ground independently or with the use of a cane
• No concurrent neurological disorders or orthopedic conditions that interfere with their ability to walk
• No prior experience walking on a split-belt treadmill
• Normal or corrected to normal vision
• The ability for them or a guardian to provide informed consent.

Inclusion criteria for neurotypical adults are:

• No musculoskeletal conditions or injuries that limit walking ability within the last two years
• No history of neurological disorders or severe head trauma
• No prior experience walking on a split-belt treadmill
• Normal or corrected to normal vision.

Exclusion Criteria for stroke survivors are:

• Inability to walk
• Concurrent neurological disorders or orthopedic conditions that interfere with their ability to walk
• More than one stroke
• Visual neglect
• Uncontrolled hypertension
• Inability to provide informed consent.

Exclusion Criteria for neurotypical controls are:

• Inability to walk
• Concurrent neurological disorders or orthopedic conditions that interfere with their ability to walk
• Uncontrolled hypertension
• Inability to provide informed consent.

The Principal Investigator, is the leader of the Stroke Initiative for Gait Data Evaluation (STRIDE) database, available at The Archive of Data on Disability to Enable Policy and research (ADDEP, https://www.icpsr.umich.edu/web/pages/ADDEP/), a joint initiative of the Center for Large Data Research and Data Sharing in Rehabilitation (CLDR). ADDEP is supported by grant P2CHD065702 awarded to the CLDR by the NIH - National Institute of Child Health and Human Development, through the National Center for Medical Rehabilitation Research, the National Institute for Neurological Disorders and Stroke, and the National Institute of Biomedical Imaging and Bioengineering. The investigators will request to share the data for the present study in STRIDE. The investigators will share walking kinematic and EMG data. No identifiable information will be shared.