Perturbation Training for Fall Prevention

Inclusion Criteria: Healthy Young participants * Age group: 18-55 years. * Absence of any acute or chronic neurological, cardiopulmonary, musculoskeletal or systemic diagnosis. * No recent major surgery (\< 6 months) or hospitalization (\< 3 months) * Not on any sedative drugs. * Can understand and communicate in English Healthy older adults * Age group: 56-90 years. * Absence of any acute or chronic neurological, cardiopulmonary, musculoskeletal or systemic diagnosis. * No recent major surgery (\< 6 months) or hospitalization (\< 3 months) * Not on any sedative drugs. * Ability to walk with or without an assistive device for 10 meters * Can understand and communicate in English * Berg balance scale score \<45/56. Persons with stroke * Age group: 18-90 years. * Absence of any acute or chronic neurological diagnosis except stroke (self reported) * Onset of stroke (\> 6 months) * Absence of any cardiopulmonary, musculoskeletal or systemic diagnosis. * No recent major surgery (\< 6 months) or hospitalization (\< 3 months) * Not on any sedative drugs. * Ability to walk with or without an assistive device for 10 meters * Can understand and communicate in English Exclusion Criteria: Healthy subject: * Subjects will not proceed with the test if any of the following occurs at baseline measurement: 1) HR \> 85% of age-predicted maximal heart rate (HRmax) (HRmax = 220 - age), 2) systolic blood pressure (SBP) \> 165 mmHg and/or diastolic blood pressure (DBP) \> 110 mmHg during resting), and 3) oxygen saturation (measured by pulse oximeter) during resting \< 95%. * Body weight more than 250 lbs. Healthy Older adults: * Individuals with heel bone density with a T-score \< -2, is classified as osteoporotic and will be excluded. * Individuals with mild cognitive impairment (Mini-mental State Exam score \< 25/30) will be excluded. * Subjects will not proceed with the test if any of the following occurs at baseline measurement: 1) HR \> 85% of age-predicted maximal heart rate (HRmax) (HRmax = 220 - age), 2) systolic blood pressure (SBP) \> 165 mmHg and/or diastolic blood pressure (DBP) \> 110 mmHg during resting), and 3) oxygen saturation (measured by pulse oximeter) during resting \< 95%. * 6 minute walk test. Subjects will also be screened out if on the 6 minute walk test they complain of shortness of breath or uncontrolled pain (\> 3/10 on VAS) or pulse oxygen drops \< 92% or are unable to achieve the age-specified minimal ambulation distance. * Body weight more than 250 lbs. Persons with stroke: * Individuals with heel bone density with a T-score \< -2, is classified as osteoporotic and will be excluded. * Individuals with mild cognitive impairment (Mini-mental State Exam score \< 25/30) will be excluded. * Subjects will not proceed with the test if any of the following occurs at baseline measurement: 1) HR \> 85% of age-predicted maximal heart rate (HRmax) (HRmax = 220 - age), 2) systolic blood pressure (SBP) \> 165 mmHg and/or diastolic blood pressure (DBP) \> 110 mmHg during resting), and 3) oxygen saturation (measured by pulse oximeter) during resting \< 95%. * 6 minute walk test. Subjects will also be screened out if on the 6 minute walk test they complain of shortness of breath or uncontrolled pain (\> 3/10 on VAS) or pulse oxygen drops \< 92% or are unable to achieve the age-specified minimal ambulation distance. * Body weight more than 250 lbs.