The main objective of this multi-site project is to compare the effects of 12 weeks of HIIT vs. MICT on brain plasticity. The effects of HIIT vs. MICT on cardiovascular health, psychosocial predictors of physical activity and motor function will also be compared. HIIT and MICT will be delivered through a whole-body exercise paradigm using a recumbent stepper that requires arm and leg forces. Outcomes will be assessed at baseline (T0, 0 weeks), at the end of the intervention (T1, 12 weeks) and at 8-week follow-up (T2, 20 weeks).

Background: Stroke is a major health issue in Canada, with 405,000 Canadians currently living with stroke. Exercise is an important component of stroke rehabilitation that can result in improved function and health. Traditionally, exercise rehabilitation programs for stroke employ moderate-intensity continuous training (MICT) protocols that are typically sustained for 20-30 minutes. The continuous nature of this form of training however, even at moderate intensities, is challenging for many individuals with stroke to sustain due to neuromotor impairments and poor exercise capacity. High-intensity exercise, when delivered in short interval bursts (i.e. high-intensity interval training, HIIT), may be a feasible alternative that allows higher intensities to be achieved during exercise. This is important because intensity of training is the critical factor in promoting changes in neuroplasticity and cardiovascular health, the two most important aspects of recovery and secondary prevention after stroke. Interventions implemented earlier following stroke are generally viewed to yield greater benefits, but high intensity exercise may also promote neuroplasticity and optimize cardiovascular health in later stages of recovery. Furthermore, determining if HIIT is viewed to be motivating and enjoyable for individuals post-stroke can provide insight into the sustainability of this intervention.

Objective: To compare the effects of 12 weeks of HIIT and MICT on neuroplasticity, cardiovascular health and psychosocial predictors of physical activity in individuals with chronic stroke.

Design: Participants will be recruited from two research sites and randomly allocated into HIIT or MICT. Participants will be assessed before and after the training period, and at an 8-week follow-up.

Outcomes: 1) The investigators will assess: Neuroplasticity: by measuring markers of corticospinal excitability at rest and in response to a non-invasive brain stimulation protocol applied over the primary motor cortex (M1); 2) Cardiovascular health: by measuring cardiorespiratory fitness, resting blood pressure, arterial stiffness, and waist-hip ratio; 3) Psychosocial predictors of physical activity: by measuring exercise motivation and enjoyment.

Methods: Neuroplasticity: motor evoked potentials amplitude, intracortical facilitation and short-intracortical inhibition on the lesioned and unlesioned upper limb M1 area at rest and in response to continuous theta-burst will be measured with transcranial magnetic stimulation; Cardiovascular health: cardiorespiratory fitness will be measured with a graded exercise test, resting blood pressure with an automated blood pressure monitor and arterial stiffness using applanation tonometry. Exercise motivation and enjoyment will be assessed with the Physical Activity Enjoyment Scale and the Behavioral Regulation Exercise Questionnaire-3, respectively.

Expected results: Both HIIT and MICT will result in improvements in outcomes of neuroplasticity and cardiovascular health. However, improvements with HIIT will be greater and will last longer. Participants will rate HIIT as enjoyable as MICT, and motivation for exercise will increase similarly after both interventions.

Impact: HIIT is a promising, time-efficient, and potentially more effective alternative to traditional MICT protocols that could offer an opportunity for greater improvement in motor recovery and cardiovascular health in people living with stroke.

Inclusion Criteria:

• 6-60 months following first-ever, single stroke confirmed by MRI/CT
• Living in the community and able to independently walk at least 10 meters (assistive devices permitted, as this is representative of many people who regain some walking ability following stroke but commonly with some adaptation)
• Montreal Cognitive Assessment score >20 (individuals with this score are capable to follow exercise instructions)

Exclusion Criteria:

• Significant disability as determined by modified Rankin scale score <2
• Stroke of non-cardiogenic origin or tumor
• Actively engaged in stroke rehabilitation services or a structured exercise program besides the one provided in the study
• Class C or D American Heart Association Risk Criteria
• Other neurological or musculoskeletal co-morbidities that preclude exercise participation
• Pain which is worsened with exercise
• Cognitive, communication, or behavioral issues that would limit safe exercise participation
• Contraindications to transcranial magnetic stimulation.

Results will be publish in peer-review journals.