# Cardiorespiratory Responses During High-Intensity Interval Training Prescribed by Rating of Perceived Exertion in Patients After Myocardial Infarction Enrolled in Early Outpatient Cardiac Rehabilitation

PMID: 35071350
Journal: Frontiers in cardiovascular medicine
Published: 2022-01-05
Authors: Dun Y, Hammer SM, Smith JR, MacGillivray MC, Simmons BS, Squires RW, Liu S, Olson TP

## 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.

## Population

- Eleven clinically selected post-MI patients after PCI in early outpatient cardiac rehabilitation.
- Sample size: 11
- Age: 62 [11] years, median [IQR].
- Sex: 7 men and 4 women.
- Fitness level: Baseline relative VO2peak 24.0 [6.5] ml/kg/min; authors note average baseline VO2peak was in the normal range for healthy individuals.
- Health status: Recent myocardial infarction after PCI; median BMI 33.0 kg/m2; LVEF 56 [8]%; high use of cardiac medications including beta-blockers.

## Methodology

- Prospective observational study with pre/post cardiopulmonary exercise tests and weekly metabolic gas exchange measurement during supervised HIIT.
- 8 weeks of HIIT after a 1-week moderate-intensity adaptation phase in cardiac rehabilitation.
- Mayo Clinic outpatient cardiac rehabilitation program, Rochester, Minnesota, USA.

## Protocol

- RPE-prescribed treadmill HIIT.
- Modality: Treadmill.
- Work intervals: 1 minute at Borg RPE 14-17.
- Recovery: 4 minutes at Borg RPE <12.
- Sets or repetitions: 5-8 high-intensity intervals.
- Intensity: Self-selected treadmill speed and grade to achieve RPE targets; achieved 91 [14]% VO2peak across sessions.
- Session duration: 30-40 minutes including 5-10 minute warm-up and 5-minute cooldown.
- Frequency: 3 sessions per week.
- Program length: 8 weeks.
- Progression: Number of hard intervals increased from 5 to 8; session duration from 30 to 40 minutes.

## Outcomes

### High-interval VO2 intensity
Status: improved
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
Status: improved
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
Status: no clear change
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
Status: improved
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
Status: no clear change
No adverse events related to exercise training occurred.

## Practical 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 And Adherence

- No exercise-training adverse events occurred.
- Clinical monitoring included continuous ECG telemetry and blood-pressure measurement during intervals.
- Participants were clinically selected and supervised.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/35071350/) (pubmed)
- [DOI](https://doi.org/10.3389/fcvm.2021.772815) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8767110/) (full text)

## Agent Guidance

Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.