After a stroke, brief bouts of vigorous exercise are more effective than steady moderate exercise.

“This study shows that stroke patients can also benefit from high-intensity interval training,” said Dr. Kevin Montsion, a physiotherapist who led the study as part of his doctoral studies at McMaster University in Hamilton, Ontario, Canada. “With the right support and guidance, stroke patients can safely and effectively undertake high-intensity interval training, which can significantly improve their overall health and recovery.”

The multi-center study ran from September 2018 to March 2024 and included stroke survivors 6 months to 5 years after stroke onset. Researchers randomly assigned participants to either high-intensity interval training, 3 days per week, for 12 weeks, or traditional moderate-intensity exercise sessions, 3 days per week, for 12 weeks. The high-intensity interval training protocol consisted of 10 one-minute bouts of high-intensity exercise separated by nine one-minute bouts of low-intensity exercise, for a total of 19 minutes. The moderate-intensity continuous training consisted of 20 to 30 minutes of steady moderate-intensity exercise.

The researchers then compared fitness levels, cardiovascular risk factors such as blood pressure and vascular stiffness, walking speed and walking distance between the two groups. All assessments were repeated one last time eight weeks after the exercise intervention to evaluate whether the changes were sustained over the long term.

The researchers found that:

• The HIIT group's cardiorespiratory fitness level (oxygen consumption rate during peak exercise) improved by twice as much as the moderate-intensity continuous training group. Their oxygen consumption per minute was 3.5 milliliters per kilogram of body weight (mL/kg/min) compared to 1.7 mL/kg/min in the moderate-intensity continuous training group.
• Improvements in the VIIT group remained above the clinically important threshold (1.71 mL/kg/min) at 8-week follow-up, but not in the IMIT group (0.67 mL/kg/min).
• Both the HIIT and MTI groups improved their walking endurance, measured by the distance they could walk in six minutes. At baseline, both groups were able to walk approximately 355 meters in six minutes (the distance of three American football fields). After 12 weeks of exercise, both groups had increased their walking distance by 8 meters, and after an eight-week follow-up, their walking distance had increased by 18 meters.

“This is the first randomized trial to investigate a time-efficient high-intensity interval training program that incorporates a staged, progressive approach,” said Dr. Ada Tan, physiotherapist, professor and associate dean of rehabilitation sciences at McMaster University and lead author of the paper. “We also used an adaptive recumbent stepper, which we believe will allow more people to participate in high-intensity interval training, even those who cannot walk fast enough or long enough on a treadmill.”

Limitations of the study include that study participants were more functional stroke survivors from a physical perspective and at lower risk of heart disease. The study's minimum criteria included the ability to walk 10 meters without the physical assistance of others, although the use of a cane or walker was permitted. Outcome assessments were unblinded at follow-up, which may have influenced the results. Finally, enrollment in the trial and exercise were halted for 2 years due to the COVID-19 lockdown, which may inflate the proportion of participants who discontinued the study and limit the statistical power of the analysis.

According to the American Heart Association's 2024 Update on Heart Disease and Stroke Statistics, in 2021, there were 7.44 million deaths due to stroke worldwide.

According to the study authors, future studies should look at stroke survivors with more severe physical impairment and heart disease risk.

“Stroke rehabilitation experts now have evidence to support the implementation of short-term high-intensity interval training in clinical settings. Our program has proven safe and effective in improving physical fitness and walking distance in people after stroke, important outcomes for stroke survivors,” Mr Tan said.

Research details and background:

• The study, conducted at McGill University in Montreal and McMaster University in Hamilton, Canada, involved 82 mostly white adults (50 men and 32 women) aged between 40 and 80 years. All had suffered a stroke approximately 1.8 years previously and had mild or minimal disability.
• Participants exercised on an adaptive recumbent stepper, which allows stroke patients of different abilities to exercise at high intensity.
• Assessments were conducted a total of three times: before starting exercise training (baseline, 0 weeks), immediately after exercise (post, 12 weeks), and at 8-week follow-up after the end of the intervention (i.e., 20 weeks from baseline).
• At each assessment, researchers measured cardiovascular fitness levels, including resting blood pressure, arterial stiffness, waist-to-hip ratio (calculated as waist circumference at the navel to hip circumference at the hip bone), and mobility (walking speed and distance).
• None of the participants experienced side effects during exercise, such as fatigue, shortness of breath, muscle pain, cramps, or dizziness.