Safety and improvement in exercise tolerance with interval training vs moderate-intensity continuous training in heart disease patient of very high cardiovascular risk
Question
Are supervised moderate- and high-intensity interval training safe and more effective than moderate continuous training for exercise tolerance in heart-disease patients with very high cardiovascular risk?
Summary
This quasi-experimental cardiac rehabilitation study compared supervised moderate continuous training, moderate-intensity interval training, and high-intensity interval training in 81 heart-disease patients classified as very high cardiovascular risk. Interval groups, especially the high-intensity interval group, showed larger median percentage gains in MET-load, but between-group differences were not statistically significant. No adverse cardiovascular episode was recorded during training.
Methodology
- Heart-disease patients in cardiac rehabilitation with very high cardiovascular risk, defined as at least two high cardiovascular risk factors.
- 81 participants.
- Cycle ergometer or treadmill aerobic training.
- Work intervals: Three 3-minute intervals at 80-90% heart-rate reserve.
- Recovery: Three 3-minute active pauses at 70-80% heart-rate reserve.
- Intensity: 80-90% heart-rate reserve for work intervals by Karvonen formula.
- 30 minutes including 5-minute warmup and 5-minute cooldown.
- 5 sessions per week.
- 4 to 6 weeks, after all patients completed 2 weeks of baseline MICT.
- Quasi-experimental cardiac rehabilitation intervention with three non-randomized training groups.
- Adverse cardiovascular episodes, MET-load gain, Watt-load gain, and Perceived exertion were tracked.
Outcomes
Safety
No adverse cardiovascular episode was recorded in any training session across MICT, MIIT, or HIIT.
MET-load gain
Median percentage MET-load gains were 45% for MICT, 60% for MIIT, and 85.74% for HIIT, showing a numerical trend favoring HIIT.
Between-group p=0.171; not statistically significant.
Watt-load gain
Median percentage watt-load gains were 51.51% for MICT, 44.29% for MIIT, and 48.64% for HIIT.
Between-group p=0.544; not statistically significant.
Borg perceived exertion
Median Borg values were 13 for MICT, 13 for MIIT, and 12 for HIIT.
Between-group p=0.157.
Insights
- Clinical HIIT safety evidence in very high-risk cardiac patients depends on intensive screening, telemetry, blood pressure monitoring, and cardiologist supervision.
- A 3 x 3-minute interval format with equal active recoveries is a reproducible clinical interval structure, but not directly appropriate for unsupervised consumer prescription in high-risk users.
- The study supports cautious safety framing rather than an efficacy superiority claim because improvements were not statistically different between groups.
Limitations
- Quasi-experimental and non-randomized.
- Group assignment was based on individualized medical criteria and risk.
- Very small HIIT group and imbalanced group sizes.
- Concurrent resistance training and multidisciplinary care confound aerobic protocol effects.
- No reliable method to quantify contribution of static/resistance training.
- VO2peak was calculated by load rather than measured by expired gas analysis.
- Attendance, completion, and dropout were not reported.
Safety
- No adverse cardiovascular episode occurred in any training session.
- The discussion states there were no cardiovascular episodes requiring hospitalization and no deaths.
- All sessions were supervised by a cardiac rehabilitation cardiologist and monitored by telemetry with blood pressure checks.