Cardiorespiratory Responses During High-Intensity Interval Training Prescribed by Rating of Perceived Exertion in Patients After Myocardial Infarction Enrolled in Early Outpatient Cardiac Rehabilitation
Question
Can HIIT prescribed by Borg 6-20 RPE elicit target cardiorespiratory responses and training adaptations in patients after myocardial infarction during early outpatient cardiac rehabilitation without excessive heart-rate or blood-pressure responses?
Summary
This prospective observational study tested whether rating of perceived exertion (RPE) could prescribe treadmill HIIT intensity in recently discharged myocardial infarction patients in early supervised outpatient cardiac rehabilitation. Among 11 patients who completed at least 24 sessions, RPE-guided 1-minute hard intervals with 4-minute easy intervals elicited high oxygen uptake, reproducible intensity, improved relative VO2peak by about 9%, and produced no exercise-training adverse events.
Methodology
- Eleven clinically selected post-MI patients after PCI in early outpatient cardiac rehabilitation.
- 11 participants.
- Treadmill.
- Work intervals: 1 minute at Borg RPE 14-17.
- Recovery: 4 minutes at Borg RPE <12.
- Intensity: Self-selected treadmill speed and grade to achieve RPE targets; achieved 91 [14]% VO2peak across sessions.
- 30-40 minutes including 5-10 minute warm-up and 5-minute cooldown.
- 3 sessions per week.
- 8 weeks.
- Prospective observational study with pre/post cardiopulmonary exercise tests and weekly metabolic gas exchange measurement during supervised HIIT.
- Oxygen uptake during high-intensity intervals, Relative VO2peak, Heart-rate and blood-pressure response, and Adverse events were tracked.
Outcomes
High-interval VO2 intensity
Mean VO2 during high intervals across 88 HIIT sessions was 91 [14]% of VO2peak and exceeded the 75% VO2peak lower target; final-session high intervals reached 97% VO2peak.
p<0.001 versus 75% VO2peak target; %VO2peak repeatability ICC 0.95, 95% CI 0.86 to 0.99, p<0.001.
Training workload and VO2 during intervals
Treadmill speed, grade, power, VO2, %VO2peak, energy expenditure, and ventilation increased from first to last high-intensity session.
All p<0.05 for high-intensity interval first-to-last comparisons.
Heart rate and blood pressure
RPE, HR, %HRpeak, systolic BP, and diastolic BP did not significantly increase between first and last HIIT session despite increased workload and VO2.
All p>0.05 for first versus last session comparisons on these variables.
Relative VO2peak
Relative VO2peak increased from 24.0 [6.5] to 26.1 [8.0] ml/kg/min; 9 of 11 participants improved.
Mean increase 1.9 ml/kg/min, 95% CI 0.1 to 3.8, p=0.049.
Exercise-training adverse events
No adverse events related to exercise training occurred.
Insights
- RPE can be a practical HIIT intensity guide when heart-rate targets are unreliable due to medications or unavailable testing.
- In supervised cardiac rehabilitation, short 1-minute hard intervals with 4-minute easy intervals can achieve true high-intensity VO2 demands.
- Clinical HIIT programming should include adaptation, warm-up, cooldown, supervision, and monitoring rather than simply prescribing hard intervals.
Limitations
- Small sample.
- No control group.
- No randomization.
- Single HIIT protocol and clinical setting.
- Participants had normal-range baseline VO2peak and may not represent typical post-MI patients.
- No direct comparison of RPE versus HR-based HIIT prescription.
- No direct cardiac function assessment during adaptation.
Safety
- No exercise-training adverse events occurred.
- Clinical monitoring included continuous ECG telemetry and blood-pressure measurement during intervals.
- Participants were clinically selected and supervised.