Study activity has initially suspended due to COVID-19 restrictions, but it will not resume due to the confounding influence of the pandemic on the study outcomes. The feasibility of the study protocol is limited with restrictions from the pandemic.

Chronic stroke is the leading cause of long-term disability in the United States. Post-stroke health is negatively impacted by two interrelated factors-a substantial risk of falls and limited walking activity. The risk of falling is a barrier to walking activity, with falls self-efficacy mediating the relationship between impaired physical capacity and limited activity. The ability to recover from a fall (i.e. arrest a fall before impact) is a logical, yet untested rehabilitation target to enable walking activity through sustained benefits to falls self-efficacy. Our aim is to demonstrate that fall-recovery training is feasible in stroke survivors with low falls self-efficacy. Five participants will undergo an adapted version of fall-recovery training. We will gather evidence of the implementation, adaptation, and limited efficacy of this intervention in affecting falls self-efficacy and walking activity.

The study aim is to demonstrate that fall-recovery training is feasible in stroke survivors with low falls self-efficacy. We will gather evidence of the adaptation, implementation, and limited efficacy of our intervention. This aim will be addressed with a single-group, interventional study. At baseline, fall-recovery ability will be determined from stepping thresholds in response to treadmill-delivered perturbations. Falls self-efficacy will be determined from questionnaires. Walking activity will be recorded using step counters (StepWatchTM). After three weeks of a non-active control period, we will repeat assessments. Then, participants will attend six training sessions consisting of anterior, posterior, and lateral perturbations. After training, we will repeat all assessments of balance, self-efficacy, and walking activity. We will recruit five participants with chronic stroke (i.e. >6 months after stroke). Falls self-efficacy is recorded upon registry enrollment, allowing us to recruit to our study needs. All participants must have an Activities-Specific Balance Confidence (ABC) score less than 68. Upon enrollment, the Fugl-Meyer Lower Extremity assessment and Stroke Impact Scale will be administered. Fall-recovery ability will be quantified from anterior, posterior, and lateral single-stepping thresholds. Participants will be outfitted with a harness attached to an overhead rail. As they stand on a computer-controlled treadmill (ActiveStep®, Simbex), participants will be instructed to not step in response to rapid belt translations. For each opposing pair of thresholds, a progressively challenging series of perturbations will be delivered. Thresholds are defined as the perturbation magnitudes that consistently elicit one step. Falls self-efficacy will be quantified from the ABC scale and the Falls Efficacy Scale (FES). Walking activity will be quantified as average daily steps, recorded in five-second intervals for one week by a StepWatchTM monitor on the non-paretic ankle.

Our fall-recovery training consists of 6 sessions over 3-4 weeks, each consisting of the following 5-minute series:

• Standing perturbations that induce a forward fall, necessitating multiple steps to regain stability. Separate series will focus on paretic and non-paretic steps. Participants will be instructed to "try not to fall".
• Standing perturbations that induce a backwards fall. Instructions will be to recover in a single step. This constraint is added because, unlike the multiple-step response of trip recoveries, slip recovery is dictated by first-step features. Separate series will focus on initial steps with the paretic or non-paretic limb.
• Standing perturbations that induce a lateral fall, delivered as participants stand facing the side of the treadmill. Participants will be instructed to "try not to fall". We will apply left and right perturbations large enough to elicit a step.
• Also, we will apply anterior and posterior perturbations as the participants walk. Our treadmill is equipped to deliver perturbations timed relative to foot strikes during gait.

The training intensity, as determined by the perturbation size and, if applicable, gait speed, will be small at first, progressing to more challenging levels dependent upon participant performance, safety, and comfort.

As per feasibility-study guidelines, we will gather evidence of adaptation, implementation, and limited efficacy.

Inclusion Criteria:

• Participants must be 18 years or older
• Participants must have had a single stroke of non-cerebellar origin, occurring six or more months prior to study enrollment.
• An Activities-Specific Balance Confidence (ABC) score less than 68.

Exclusion Criteria:

• More than one stroke
• Acute illness at the time of functional assessment or training
• Body mass greater than 136 kg (300 lbs) to ensure that the treadmill accelerates accurately
• Lower extremity joint replacement or shoulder joint replacement within a year prior to participation
• Dementia
• Parkinson's disease
• A history of back surgery
• A history of neck surgery
• More than one occurrence of back or neck pain in the month prior to participation
• Current back or neck pain at the time of participant enrollment
• Bulging vertebral discs
• Spine, hip, or lower extremity fracture within a year prior to participation
• Open lesions on the lower extremity
• Insulin-dependent diabetes
• Use of a pacemaker
• Use of an ostomy pouch
• Pregnancy
• Osteoporosis
• Doctor recommendation to avoid moderate physical activity or exercise
• Any neural, muscular, or skeletal condition or injury that precludes safe participation in the training or introduces a confounding factor on the study, at the discretion of the clinician or study staff

1 month (from study start date: February 21, 2020 to the day the study was halted: March 13, 2020).

The study was halted due to the COVID-10 pandemic after one participant was enrolled and completed baseline assessments. The study did not resume and participation was terminated by the investigator.