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Updated: Jun 27, 2026
A Real-World High-Intensity Interval Training Protocol for Cardiorespiratory Fitness Improvement
Published on: February 22, 2022
Time-Course of Physiological Adaptations to High-Intensity Interval Training-Based Cardiac Rehabilitation After
Kristina Skroce1,2, Dijana Travica Samsa1,2,3, Marina Njegovan2
1Faculty of Medicine, University of Rijeka, 51000 Rijeka, Croatia.
Insights
High-intensity interval training (HIIT) significantly improved cardiorespiratory fitness and left ventricular ejection fraction in stable post-STEMI patients. Cardiac stress biomarkers remained stable, indicating a safe and effective rehabilitation approach.
Area of Science:
- Cardiology
- Exercise Physiology
- Rehabilitation Medicine
Background:
- High-intensity interval training (HIIT) is increasingly utilized in exercise-based cardiac rehabilitation (ebCR) following myocardial infarction (MI).
- The precise timeline of physiological, cardiac, biochemical, and functional adaptations to HIIT in post-MI patients requires further elucidation.
Purpose of the Study:
- To characterize the temporal sequence of adaptations during a 12-week supervised HIIT program in stable post-STEMI patients.
- To assess changes in cardiorespiratory fitness, cardiac function, biomarkers, and functional capacity.
Main Methods:
- Stable post-STEMI patients and healthy controls completed 12 weeks of supervised HIIT (3 sessions/week).
- Assessments included cardiopulmonary exercise testing (CPET), echocardiography, blood biomarkers, body composition, 6-minute walk test (6MWT), and RAND-36 at baseline and at 4, 8, and 12 weeks.
- Longitudinal changes were analyzed using non-parametric statistical tests.
Main Results:
- Both groups demonstrated significant improvements in peak oxygen consumption (VO2peak) and 6MWT distance.
- Left ventricular ejection fraction (LVEF) improved significantly in the MI group early in the intervention, while LV dimensions remained stable.
- N-terminal pro-B-type natriuretic peptide (NT-proBNP) levels showed no significant change, and C-reactive protein (CRP) decreased in the MI group.
Conclusions:
- Supervised HIIT in stable post-STEMI patients leads to improvements in VO2peak and LVEF without concerning elevations in cardiac stress biomarkers.
- These findings suggest HIIT is a potentially safe and effective component of cardiac rehabilitation.
- Further evaluation in larger randomized controlled trials is warranted to confirm these descriptive findings.
Abstract:
Background: High-intensity interval training (HIIT) is increasingly used in exercise-based cardiac rehabilitation (ebCR) after myocardial infarction (MI), yet the temporal sequence of physiological, cardiac, biochemical, and functional adaptations remains incompletely characterized. Methods: Stable post-STEMI (ST-segment elevation myocardial infarction, MI-group) and previously inactive participants without known cardiovascular, metabolic or systemic disease (CTRL group) completed 12-week supervised outpatient HIIT (4 × 4 min intervals at 85-90% HRpeak (peak heart rate), ~80-90% of VO2peak, 3 sessions/week). Assessments were performed at baseline (T1), 4 (T2), 8 (T3), and 12 weeks (T4), including cardiopulmonary exercise testing (CPET), echocardiography, blood biomarkers, body composition, six-minute walk test (6MWT), and RAND-36. Longitudinal changes were analyzed using Friedman tests with Dunn post hoc comparisons; between-group differences used Mann-Whitney U tests with Holm correction. Results: VO2peak increased significantly in both groups (p < 0.001), increasing by ~22% from T1 to T4 in MI (median 20.1 to 24.5 mL·kg-1·min-1) and ~23% from T1 to T4 in CTRL (median 22.3 to 27.6 mL·kg-1·min-1). LVEF (left ventricular ejection fraction) improved early in MI, increasing from 52.5% (50.0-55.0) at T1 to 57.5% (55.2-58.7) at T2 and up to 60% (55.8-60.0) at T4 (all p < 0.001), while LV dimensions remained stable. NT-proBNP (N-terminal pro-B-type natriuretic peptide) showed no significant longitudinal change (p = 0.510), and CRP (C-reactive protein) decreased from 2.1 to 0.7 mg·L-1 (p = 0.008) in MI. Both groups improved body fat % and 6MWT distance (p < 0.001). Conclusions: In low-risk stable post-STEMI patients, longitudinal changes during supervised HIIT-based ebCR were consistent with improved VO2peak and LVEF, without clinically relevant increases in cardiac stress biomarkers. However, due to the observational design and absence of clinical comparator groups, these findings should be interpreted as descriptive and support further evaluation in larger randomized studies.
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