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Updated: Aug 6, 2026
A Real-World High-Intensity Interval Training Protocol for Cardiorespiratory Fitness Improvement
Published on: February 22, 2022
Comparison of high-intensity interval training protocol designs on accumulated time ≥ 90% V̇O₂max: a network
Steffen Held1, Ludwig Rappelt2, Florian Micke3
1Department of Sport and Management, IST University of Applied Sciences, Duesseldorf, Germany. sheld@ist-hochschule.de.
Background:
Accumulated time ≥ 90% of maximal oxygen uptake (V̇O2max) during high-intensity interval training (HIIT) represents a key stimulus for aerobic adaptations. Thus, this network meta-analysis (NMA) aimed to compare different HIIT protocol structures with respect to accumulated time ≥ 90% V̇O2max using direct and indirect evidence.
Methods:
We systematically searched PubMed, Web of Science, and SPORTDiscus up to January 31st, 2026 for controlled HIIT studies reporting accumulated time ≥ 90% V̇O₂max in healthy athletes. HIIT protocols were classified using predefined operational rules based on interval duration, work-to-rest structure, intensity pattern, and within-session progression. We conducted a frequentist NMA using standardized mean differences (SMD) within a random effects model, with even long intervals as the reference condition, and added local inconsistency and contribution diagnostics.
Results:
Nineteen publications contributed 20 study units, including 240 athletes (25.5 ± 5.3 years; V̇O₂max 60.5 ± 8.1 ml·kg⁻¹·min⁻¹). The network demonstrated substantial heterogeneity and significant inconsistency (I² = 69.2%, 95% CI 49.9% to 81.0%; total Q = 55.12, df = 17, p < 0.0001; between-design Q = 20.78, df = 6, p = 0.002). None of the HIIT approaches differed significantly from even long intervals in accumulated time ≥ 90% V̇O₂max. Point estimates were highest for decreased-duration (SMD = 0.87, 95% CI -0.30 to 2.04) and varied-intensity protocols (SMD = 0.54, 95% CI -0.42 to 1.49), whereas 1:1 blocks showed the lowest point estimate (SMD = -0.68, 95% CI -1.40 to 0.04). P-score ranking favored decreased-duration (89.6%), followed by varied-intensity (76.7%) and decreased-intensity protocols (68.4%), while 1:1 blocks ranked lowest (2.8%).
Conclusion:
No HIIT protocol structure showed clear superiority for accumulated time ≥ 90% V̇O₂max. Decreased-duration and varied-intensity protocols ranked highest, but these rankings were exploratory because all reference comparisons were statistically non-significant and the network showed substantial heterogeneity, significant inconsistency, and sparse evidence for several nodes. Protocol selection should therefore prioritize feasibility, athlete characteristics, and workload-matching considerations rather than ranking alone.
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