Exercise- we all need it and yet many of us do not get enough. Currently, the recommendations from the World Health Organization are that both children and adults get 150-300 minutes of moderate intensity or 75-150 minutes of vigorous intensity exercise per week. However, about 33% of adults and 80% of adolescents globally do not meet these guidelines.1 Why do we have such trouble meeting these guidelines? The biggest reason appears to be time.
Unsurprisingly, a perceived lack of time is the biggest limiter for many when it comes to exercise. Any form of exercise, from the lowest intensity walk to the highest intensity power-lifting or sprint session, is beneficial. The biggest benefit to high-intensity interval training (HIIT) is that it takes less time when compared to a steady-state workout. However, are there other benefits? The science suggests that there may be.
HIIT is known for its short duration of workouts, with intervals ranging between 15 seconds and 4 minutes, in addition to its high intensity.3 A typical HIIT workout includes short periods of an “all out” effort (>80% maximum heart rate, >90% maximum oxygen uptake (VO2 max), or >75% maximum power) with short rests or lower intensity activity sprinkled in for recovery.2 The positive changes seen in maximum oxygen uptake, better heart rate control, fat burning, muscle building, and aerobic and anaerobic functioning make HIIT appealing to those who want to increase their fitness but have little time to do so.1,3 Also, it is interesting to note that the energy burn continues for hours after the workout is over.3
The biggest gains from HIIT workouts are in the cardiovascular and muscular systems including oxygen uptake in the muscles.1 HIIT seems to recruit more, and varied, types of muscle fibers (fast and slow twitch) making a noticeable gain in muscular strength and power.6 It is important that adequate rest is taken in between intervals to ensure that maximum effort can be exerted in every interval and maximum benefit gained.1
When looking at the bigger picture, HIIT also has been shown to reduce the risk for cancer (breast and colon) and arthritis (both osteoarthritis and rheumatoid), reduce falls, improve mood, lower cardiovascular risk, increase insulin sensitivity, and decrease the risk for type 2 diabetes, in addition to weight loss.1 Although these benefits can also be observed with steady-state exercise, it is worth mentioning since HIIT workouts may be chosen more frequently by busy people.
It is important before starting a HIIT program (or any exercise program) that one should consult with their physician to ensure they are in good enough health to perform the specific exercises. This is especially important for the elderly, deconditioned, obese, or those with chronic health conditions including: arrhythmia or uncontrolled blood pressure.2 Intensity may need to be decreased when first initiating a HIIT program to remain safe.
On the other hand, steady-state is exactly what it sounds like. This exercise regimen uses low to medium intensity movement over a longer period of time (typically, at least 30-60 minutes). Many people would consider walking and running to be forms of steady-state exercise; however, hiking, rucking, biking, and swimming also provide this level of effort and can provide variation. While HIIT focuses on working at >80% of the maximum heart rate, steady-state focuses on exercising at around 45-65% of the maximum heart rate, although this can vary with experience and fitness levels. Some of the benefits include fat loss, an easier recovery and shorter recovery time, and improved endurance and aerobic capacity (maximum amount of oxygen that the body can use during exercise).4
In some cases, steady-state is also known as “zone 2” training during which your heart rate remains steady in your “zone 2” which is about 60-70% of the maximum heart rate. Training with a heart rate between 45-70% of the maximum for about 80% of the total weekly exercise minutes leads to the great physiologic changes seen with HIIT but takes much more time to obtain. The changes include as stronger heart (and lower resting heart rate), more efficient mitochondria (and production of cellular energy), and the use of fat as an energy source which can facilitate longer workouts.5
There are some drawbacks to relying on steady-state workouts though. Of course, the biggest is the longer amount of time it takes to complete and the subsequent boredom that may accompany this. There is also the risk for overuse injuries if there is little variation in the routine. Finally, steady-state is more likely to lead to plateaus in fitness, weight loss, and muscle gains. There is even a chance that muscle mass could be lost if adequate nutrition (calories and protein intake) is not maintained to support the prolonged duration of exercise.5
So, does it make a difference if we choose HIIT or steady-state? The brief answer is- it might.
First and foremost, the brief duration and constant change in intensity can keep the HIIT exercise routine interesting and more enjoyable; however, it has also been seen that the intensity may be a turn-off for some.1,6 Another notable finding, in a research study investigating both HIIT and steady-state workouts, showed that the predicted variances in improvement were not as great as expected when looking at untrained young people. Though the biggest gain appeared to be in VO2max, this seemed to be noted more frequently in well-trained individuals versus untrained.6
Simply put- the best exercise routine for you is the one that you will do regularly and for more than a few weeks. Whether steady-state or HIIT, the ultimate goal should be to improve health and stay active. It is easy to remain sedentary in modern life but our bodies were made to move and good health requires it.
References:
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;18(13):7201. doi:10.3390/ijerph18137201. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8294064/
Hiit(High intensity interval training). The Nutrition Source. November 10, 2021. Accessed September 1, 2024. https://nutritionsource.hsph.harvard.edu/high-intensity-interval-training/
Health C. High-intensity workouts can help you get fit fast, but preparation is key. cultivating-health. Accessed September 1, 2024. https://health.ucdavis.edu/blog/cultivating-health/high-intensity-workouts-can-help-you-get-fit-fast-but-preparation-is-key/2022/09
Golden N. What is steady-state cardio? Accessed September 1, 2024. https://blog.nasm.org/what-is-steady-state-cardio
Pippin CM. What is steady state cardio and how to use it | pippin performance. pippin-performance. December 31, 2023. Accessed September 1, 2024. https://www.pippinperformance.com/post/what-is-steady-state-cardio-and-how-to-use-it
6. Foster C, Farland CV, Guidotti F, et al. The effects of high intensity interval training vs steady state training on aerobic and anaerobic capacity. J Sports Sci Med. 2015;14(4):747-755. Accessed September 1, 2024. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4657417/ Assessed and Endorsed by the MedReport Medical Review Board