What You'll Learn
Table of Contents
What Endurance Training Is
Endurance training develops the body's ability to sustain work over time. Its main targets are maximal oxygen uptake (VO2max), the lactate threshold where fatigue accelerates, and movement economy — how little energy a given pace costs.
These are related but distinct endpoints. A program that improves VO2max will not necessarily produce the biggest gain in running economy, which is why the most useful endurance plans are built around a specific limiter rather than generic 'cardio.'
What Science Says
The clearest signal is that HIIT is not a universal replacement for steady endurance work. A meta-analysis in highly trained athletes found HIIT improved anaerobic threshold compared with continuous training, but rated the certainty low and the heterogeneity high. A separate review in runners found HIIT improved running economy relative to moderate-intensity continuous training, while continuous training produced a larger VO2max effect.
The training-pattern literature points the same way. A 2024 review of polarized training found that combining a large volume of low-intensity work with a smaller dose of high-intensity work seems effective for VO2max and work economy in the short term, with a distribution around 15–20% high intensity and 75–80% low intensity looking most favourable. The practical message is consistent: successful endurance athletes integrate easy volume, threshold work and selected hard sessions rather than chasing constant maximal efforts.
Strong Evidence
HIIT can improve anaerobic threshold in highly trained athletes, though the supporting evidence is limited and heterogeneous.
HIIT can improve running economy relative to moderate-intensity continuous training.
Moderate-intensity continuous training can produce larger VO2max gains than HIIT in the reviewed evidence.
Polarized training appears effective for VO2max, VO2peak and work economy in the short term.
Moderate Evidence
A split with most work at low intensity and a smaller share at high intensity is a reasonable default for many endurance athletes.
Lactate threshold work matters, but the exact dose, placement and intensity distribution still need to be individualized.
The best endurance program is probably outcome-specific: one block may prioritise VO2max, another threshold, another economy.
Practical Applications
If the main limitation is VO2max, more continuous aerobic work may deserve priority.
If the main limitation is running economy or threshold, HIIT or threshold-focused work becomes more attractive.
Use a polarized distribution as a default framework: mostly easy work, some very hard work, and enough threshold work to connect them.
Keep HIIT purposeful — it is one tool inside a broader endurance system, not the whole system.
Monitor progress with the endpoint that matters most for your sport: VO2max, threshold, economy or race performance.
Common Mistakes
Treating HIIT as automatically superior for every endurance outcome.
Using too much high intensity and too little easy volume.
Judging a program only by VO2max when race performance may depend more on threshold or economy.
Copying elite intensity distributions without matching them to your training age and recovery capacity.
Turning endurance training into repeated fatigue management instead of adaptation.
FAQ
Does HIIT beat steady-state training?
Not universally. HIIT improved running economy and threshold in the studies reviewed, while continuous training often did better for VO2max.
Is polarized training worth using?
Yes, as a practical framework, especially when you want to balance aerobic base work with higher-intensity development.
What intensity split looks best?
Roughly 15–20% high-intensity work with 75–80% low-intensity work looked most favourable, though the number of studies is small.
Should I focus on VO2max or threshold?
It depends on your sport and your limiter; they respond differently to training.
Is lactate threshold training useful for distance running?
Yes, but it should be individualized and embedded in a broader plan, not treated as a standalone magic zone.
Scientific References
- Pereira PE, Esteves G, Carvas N, et al. Effects of high-intensity interval and moderate-intensity continuous training on the anaerobic threshold of highly trained athletes. J Sports Med Phys Fitness (2024).
- Feng Y, Li D, Liu Y, et al. HIIT and Moderate-Intensity Continuous Training Affect Running Economy in Endurance Runners: A Systematic Review and Meta-Analysis. Journal of Human Kinetics (2024).
- Nøst HL, Aune MA, van den Tillaar R. The Effect of Polarized Training Intensity Distribution on Maximal Oxygen Uptake and Work Economy Among Endurance Athletes: A Systematic Review. Sports (2024).
Medical Disclaimer
This article is educational and not medical advice. Adjust training, nutrition and supplementation with a qualified professional, especially if you have medical conditions, take medication, are pregnant, or have heart, kidney or orthopedic concerns.