The long-term objective of this research is to develop an efficacious training paradigm to enhance stroke survivors' defense mechanisms against falls and possibly reduce healthcare cost. The Centers for Disease Control and Prevention estimates the direct medical cost for fall related injuries to be $34 billion annually. Forty percent to 70% of community-dwelling stroke survivors experience detrimental falls each year and tend to have 1.5 to 4 times higher risk of hip fracture than their healthy counterparts; with only less than 40% of those individuals regaining independent mobility. Falls, thus not only affect activities of daily living but also reduce mobility, increase risk of second stroke and mortality. Despite potential financial and functional implications of falls in this population, health-care personnel are limited in their ability to develop and validate interventions to reduce fall-risk for them. Further emphasis is placed on locomotor training with focus on enhancing paretic limb function. The project design consists of a randomized controlled trial to examine the ability of chronic stroke survivors to acquire, generalize and retain adaptations to slip-perturbation training for not only mitigating fall risk but also improving walking function. It also explores translation of this paradigm to the sub-acute population. The paradigm is novel in that it targets contributions of the paretic vs. non-paretic limbs on fall-risk through a bilateral training paradigm that involves training the non-paretic side first and then paretic to facilitate acquisition of fall-prevention skills on the paretic side, which may otherwise take longer to acquire training effects. The longer-term benefits of such perturbation training, targeting both limbs for reducing falls will be assessed not only in the laboratory but also in real life via wearable sensors, along with improved community walking function. The hypothesis of this study if supported by the results will provide an evidence-supported training protocol to reduce the fall-risk not only in people living with hemiparetic stroke but also among survivors of other acquired unilateral cortical lesions.

Approximately 800,000 Americans suffer a stroke every year and 689,450 reported having short and long-term disabilities leading to dependence in activities of daily living. It has been reported that stroke survivors experienced detrimental falls each year and most occurring during walking. The likelihood of experiencing a fall upon discharge from rehabilitation being significantly higher than during the rehabilitative phase. Falls resulting from environmental perturbations such as slips contribute to a significant percentage of these falls. Hence, it is important to develop innovative and effective paradigms for fall-risk reduction in chronic as well as sub-acute stroke survivors. The purpose of this research is to understand the effect of bilateral slip-perturbation training protocol targeting training both paretic vs. non-paretic limbs on fall-risk reduction and prevention. Also, to find its effect on increasing community ambulation in community dwelling stroke survivors.

Participants in this study will be individuals with chronic (> 6 months) hemiparesis following stroke or individuals with sub-acute stroke (> 6weeks and < 6 months), ambulatory (with or without assistive device) and more than 21 years of age. Subjects will be screened for the inclusion criteria. If subjects pass the screening, they will go through the full clinical balance assessment and laboratory dynamic stability test. The chronic stroke survivors will be randomized into two groups: - Group A: Slip training group; Group B: Control group. While, the sub-acute stroke survivors will be randomized into two groups: - Group C: Slip training group; Group D: Control group.

For the slip training groups (A and C), all subjects' normal walking pattern and their recovery responses to slip will be recorded with a motion tracking system (including videotaping) while they walk across an instrumented area along a straight path in the lab. A slip will be induced after a subject steps on a low-friction platform.

For the chronic stroke subjects, baseline activity monitoring using wearable sensors will be performed for up to four weeks prior to the training session followed by activity monitoring for 12 months. While for the sub-acute stroke subjects, it would be done for 6 months.

For groups A and B, the follow-up stability test will be at 6 and 12 months post-training session, which will consist only of one slip induced on the training side and contralateral side. For groups C and D, follow-up session is 6 months post training session.

Incidence of falls and physical activity will be monitored between training and re-test sessions through falls, activity monitoring-questionnaire to describe details of the falls and through the wearable sensors for groups A, B, C and D.

Inclusion Criteria:

• Subjects will have to be ambulatory (with or without assistive device) with self-reported chronic (> 6 months) stroke-induced hemiparesis confirmed by participants' physician and medically cleared. Evidence of unilateral brain lesion confirmed by an imaging study (e.g. CT or MRI).
• Subjects with no other acute and significant neurological, cardiopulmonary, musculoskeletal or systemic diagnosis or have undergone a recent major surgery (<6 months) or hospitalization (<3 months) and not on any sedative drugs
• Ability to walk at least 10m with or without assistive device which includes use of ankle orthosis or functional electrical stimulation devices (which is equivalent to having a score of> 4, dependent supervision on Functional Ambulatory category scale)

Exclusion Criteria:

• Severe osteoporosis (Ultrasound score < -2)
• Cognitive impairment (Mini Mental State Exam score<25)
• Aphasia (<71% on Mississippi Aphasia Screening Test)
• Severe depression ( > 15 on Geriatric Depression Scale)
• Severe obesity (BMI >35Kilogram/m2)
• Complains of shortness of breath, or uncontrolled pain (> 3/10 on VAS), or if pulse oxygen drops <92% on the 6 minute walk test (for endurance)
• Uncontrolled hypertension (resting systolic blood pressure > 165 mmHg and/or diastolic blood pressure > 110mmHg)
• Resting heart rate > 85% of age-predicted maximal heart rate
• Resting oxygen saturation <95%