Submaximal Exercise Testing to Dose High-Intensity Interval Training After Stroke: The FAST Randomized Clinical Trial

Importance High-intensity interval training (HIIT) improves peak oxygen uptake (VO 2 peak) and walking post-stroke. However, previous HIIT trials have primarily implemented maximal exercise testing, limiting clinical implementation. Objective Evaluate the preliminary efficacy of HIIT, compared to moderate-intensity continuous training (MICT) using a submaximal exercise test. Hypothesis: HIIT will produce greater improvements than MICT in VO 2 peak, vascular measures, and walking outcomes. Design This was a randomized preliminary efficacy trial conducted between July 2023 and December 2025. Setting University of Kansas Medical Center. Participants Participants with chronic stroke, 20-85 years of age, were randomized to HIIT or MICT. Intervention HIIT and MICT were performed on a total-body recumbent stepper 3 times per week for 4 weeks, with intensity prescribed using peak power output (PPO) to achieve target heart rate zones derived from a submaximal exercise test. HIIT was performed for 25 minutes with 1-minute vigorous-intensity intervals (65-95% PPO) interspersed with 1-minute active recovery intervals. MICT was performed continuously at 45-65% PPO for 25 minutes. Main Outcomes The primary outcome was change in predicted VO 2 peak. Secondary outcomes included middle cerebral artery velocity, peripheral vascular function, and arterial stiffness with gait speed and walking endurance as tertiary outcomes. Results Forty-nine participants (HIIT: n=25, MICT: n=24) were randomized (62.4(12.5) years, 42.9% female), attended 99.5(2.0)% of sessions, and achieved target intensity zones. No study-related serious adverse events occurred. Our results showed no significant between-group differences (p=0.54) for study outcomes. Both groups significantly improved VO 2 peak (HIIT: +1.13 mL•kg -1 •min -1 (95% CI: 0.05-2.21), p=0.04; MICT: +1.58 mL•kg -1 •min -1 (95% CI: 0.18-2.97), p=0.03) and with fast gait speed and walking endurance. Peripheral vascular function significantly improved following HIIT. Conclusions and Relevance HIIT can be safely implemented in individuals with chronic stroke using a submaximal exercise test. Both HIIT and MICT elicited clinically meaningful gains in VO 2 peak and walking. However, only HIIT led to a significant improvement in peripheral vascular function, suggesting a biologic signal for intensity-dependent vascular adaptation. Trial Registration ClinicalTrials.gov identifier: NCT05936008 . Key Points Question In individuals with chronic stroke, does high-intensity interval training (HIIT) improve predicted VO₂peak more than moderate-intensity continuous training (MICT)? Findings In this randomized clinical trial of 49 participants with chronic stroke, both HIIT and MICT achieved prescribed intensity targets with high adherence and resulted in clinically meaningful improvements in predicted VO₂peak and walking outcomes after 4 weeks, with no significant between-group difference in our primary outcome of VO₂peak. Meaning These findings suggest that when aerobic exercise is prescribed to achieve target intensity, both HIIT and MICT produce meaningful improvements in fitness and walking after stroke, supporting the importance of appropriate exercise dosing.