# High-intensity interval training improves metabolic syndrome and body composition in outpatient cardiac rehabilitation patients with myocardial infarction

PMID: 31412869
Journal: Cardiovascular Diabetology
Published: 2019-08-14
Authors: Dun Y, Thomas RJ, Smith JR, Medina-Inojosa JR, Squires RW, Bonikowske AR, Huang H, Liu S, Olson TP

## Question

Is supervised HIIT associated with greater improvements in metabolic syndrome and body composition than MICT among MI patients in early outpatient cardiac rehabilitation?

## Summary

In a retrospective Mayo Clinic cardiac rehabilitation cohort, myocardial infarction patients with metabolic syndrome who self-selected HIIT after an initial MICT week improved metabolic syndrome severity, several metabolic risk factors, body fat, lean mass, and VO2peak more than those who continued MICT. The study was observational and selected only people completing all 36 rehabilitation sessions.

## Population

- Outpatient cardiac rehabilitation patients after MI with metabolic syndrome.
- Sample size: 56
- Age: MICT 69 +/- 14; HIIT 68 +/- 10 years
- Sex: 36% female in both groups
- Fitness level: Early outpatient cardiac rehabilitation patients
- Health status: Recent MI with metabolic syndrome

## Methodology

- Retrospective observational cohort study
- 36 cardiac rehabilitation sessions, usually 12 weeks
- Mayo Clinic outpatient cardiac rehabilitation program
- Controlled study design.

## Protocol

- Cardiac rehab HIIT.
- Modality: Treadmill, cycle ergometer, or recumbent stepper.
- Work intervals: 30-60 seconds initially, progressed to 2-4 minutes.
- Recovery: 1-5 minutes active recovery.
- Sets or repetitions: 4 intervals progressing to 5-8 intervals.
- Intensity: RPE 15-17 for high intervals; recovery RPE <14.
- Session duration: 20-45 minutes.
- Frequency: Up to 3 supervised nonconsecutive days/week.
- Program length: 36 CR sessions, usually 12 weeks.
- Progression: Increased interval duration and number over CR.
- MICT.
- Modality: Treadmill, cycle ergometer, or recumbent stepper.
- Work intervals: Continuous.
- Sets or repetitions: 20-45 minutes continuous.
- Intensity: RPE 12-14.
- Session duration: 20-45 minutes.
- Frequency: Supervised CR sessions.
- Program length: 36 CR sessions, usually 12 weeks.
- Progression: Usual CR progression.

## Outcomes

### MetS
Status: improved
HIIT reduced MetS presence and severity more than MICT.

Relative risk 0.5, 95% CI 0.33-0.75, p<.001; MetS z-score change -3.6 +/- 2.9 vs -0.8 +/- 3.8, p<.001.

### Risk factors
Status: improved
HIIT improved waist circumference, fasting glucose, triglycerides, and diastolic blood pressure more than MICT.

FBG -25.8 vs -3.9 mg/dl, p<.001; TG -67.8 vs -10.4 mg/dl, p<.001; DBP -7 vs 0 mmHg, p=.001.

### Body composition
Status: improved
HIIT reduced fat mass/body fat and increased lean mass more than MICT.

Fat mass -2.1 +/- 2.1 vs 0 +/- 2.2 kg, p=.002; lean mass +0.9 +/- 1.9 vs -0.9 +/- 3.2 kg, p=.01.

### VO2peak
Status: improved
HIIT increased VO2peak more than MICT.

Change +5.0 +/- 2.5 vs +1.4 +/- 0.9 ml/kg/min, p=.03.

## Practical Insights

- RPE-based intervals can be used when beta blockers or other medications make HR targets less reliable.
- HIIT evidence in cardiac populations depends on supervised CR infrastructure.
- Retrospective self-selection makes causality weaker despite large improvements.

## Limitations

- Retrospective observational design.
- Self-selection into HIIT after week 1.
- Only patients completing all 36 CR sessions and follow-up tests were included.
- Only 36% women.
- Not powered for safety.

## Safety And Adherence

- All included patients completed 36 CR sessions without a major adverse event.
- The study was not designed or powered to demonstrate HIIT safety after MI.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/31412869/) (pubmed)
- [DOI](https://doi.org/10.1186/s12933-019-0907-0) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6694483/) (full text)

## Agent Guidance

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