How Effective Are HIIT Workouts?

The science is abundantly clear, high intensity interval training is one of the best interventions that can be done for improving both health and performance. The good news is that you have found a way to remain in extremely good fitness, the bad news is that it’s not going to be easy it terms of effort. High intensity interval training is very challenging, but without a doubt, an extremely effective.

4 min read
Sean Klein
Written by
Sean Klein
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In This Resource
  • Performance Benefits
  • VO2 Max
  • Health Benefits
  • Glucose Tolerance and Insulin Sensitivity
  • Reduced Risks of Multiple Cancers
  • Other Health Benefits
  • Sustainable Training
  • Time Effective
  • Enjoyable
  • Issues with HIIT
  • References

Performance Benefits

VO2 Max

VO2 max is the maximum amount of oxygen intake, it is one of the key factors for performance in endurance sports and a good marker of cardiovascular health. This increase in VO2 max is due to numerous physiological adaptations including, and increase in stroke volume, maximal cardiac output, maximal a-vO2 difference (improved gas exchange), capillary density, increased red blood cell volume and hemoglobin mass. All this means that our ability to carry oxygen is improved, meaning improvement in cardiovascular performance. (1)

This all might sound very technical, but understanding the fact that when we do HIIT it creates physiological adaptations to our heart, helps us understand why it’s beneficial. This is often so obvious with resistance training, when we lift weights we see our strength increase and see our muscle grow. The adaptations can be more “hidden” within us when we develop an excellent cardiovascular system.

Therefore if you are looking to improve your cardiovascular performance, you need to be performing HIIT on a regular basis (1-2 times a week). Alongside other styles of cardiovascular training including low and medium intensity training sessions. This increase in VO2 max from these short outputs can also help improve endurance efforts as a higher intensity can be maintained for extended periods of time.

Health Benefits

Glucose Tolerance and Insulin Sensitivity

The role insulin plays in maintaining normal glucose homeostasis is crucial to our health and if this ability is degraded through poor glucose tolerance we put ourselves at risk of type two diabetes. A lack of exercise is known to cause a reduction in glycemic control. Numerous studies have shown that HIIT is effective in both the long and short term for improving insulin sensitivity and glucose tolerance . (2)

Reduced Risks of Multiple Cancers

High intensity interval training has also been shown to reduce the chance of both colon cancer and breast cancer.

Other Health Benefits

  • Improved mood and decreased feelings of depression and anxiety
  • Lower risk of cardiovascular disease
  • Helps relief from low back pain
  • For a full breakdown of health benefits of HIIT please read through this meta-analysis . (3)

    Sustainable Training

    Time Effective

    The design of HIIT means the the sessions rarely last longer the 15 minute of out put and 30 minutes in total from start to finish. The major hurdle people have to building an exercise routine is a lack of time, making HIIT a perfect go to option.


    HIIT also has a strange sense of enjoyment attached to it. This can be seen in how the protocols adherence rates is higher than lower intensity cardiovascular training, and also through the popularity of CrossFit and other HIIT style of training. (4)

    Issues with HIIT

    HIIT is by its nature extremely fatiguing due to the very high intensity, making it a very difficult protocol to perform regularly during the week. This is why doing one or two HIIT sessions during the week is likely the best way forward for long term progression.

    It can also be hard when dealing with stress in other areas of life or coming back from a period of being sedentary. This is why doing a mix of low intensity and high intensity cardiovascular output is a very effective way to maintain health and performance throughout the long term, when dealing with stress or injury you can fall back on to the habit of lower intensity outputs and when leaning into your exercise regime you can put more emphasis on HIIT.


  • Atakan MM, Li Y, Koşar ŞN, Turnagöl HH, Yan X. Evidence-Based Effects of High-Intensity Interval Training on Exercise Capacity and Health: A Review with Historical Perspective. Int J Environ Res Public Health. 2021 Jul 5;18(13):7201. doi: 10.3390/ijerph18137201. PMID: 34281138; PMCID: PMC8294064.
  • Babraj JA, Vollaard NB, Keast C, Guppy FM, Cottrell G, Timmons JA. Extremely short duration high intensity interval training substantially improves insulin action in young healthy males. BMC Endocr Disord. 2009 Jan 28;9:3. doi: 10.1186/1472-6823-9-3. PMID: 19175906; PMCID: PMC2640399.
  • Atakan, M.M. et al. (2021) ‘Evidence-based effects of high-intensity interval training on exercise capacity and health: A review with historical perspective’, International Journal of Environmental Research and Public Health , 18(13), p. 7201. doi:10.3390/ijerph18137201.
  • Thum JS, Parsons G, Whittle T, Astorino TA. High-Intensity Interval Training Elicits Higher Enjoyment than Moderate Intensity Continuous Exercise. PLoS One. 2017 Jan 11;12(1):e0166299. doi: 10.1371/journal.pone.0166299. PMID: 28076352; PMCID: PMC5226715.
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    This resource was written by Sean Klein. Sean Richard Klein has thousands of hours of coaching experience and a BSc in Sports Science with Management from Loughborough University. He owns a gym in Bayonne France, CrossFit Essor, which runs group classes and a Personal training studio.

    Sean Klein


    Programme is a workout app that plans every workout for you

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