High-intensity interval training (HIIT) has grown in popularity in recent years and is now a well-known exercise modality. “High intensity” refers to the target heart rate range that an individual should achieve, while “interval” refers to the interrupted nature of exercise. Put together, HIIT is composed of short periods of exercise at near maximal levels, defined by most as reaching >70-85% peak heart rate, alternating with longer periods of rest or lighter activity (1-3). Many different types of exercise can be adapted into HIIT, including cycling, running, and certain bodyweight exercises. It is associated with several health benefits, such as increasing metabolism, improving cardiorespiratory health, reducing body fat, and improving blood sugar control. It is also a time-efficient workout – in many cases, a full session lasts only 30 minutes (2-4).
One major benefit of HIIT is its ability to reduce body fat. High levels of body fat, especially in the abdominal area, are strongly associated with a number of chronic conditions, including heart disease and diabetes. With the growing epidemic of obesity, developing clear recommendations on physical activity (and nutrition) is more important than ever (2,4). Researchers in France performed a meta-analysis to ask whether HIIT is a time-efficient way to decrease fat-mass deposits. 617 participants across 39 studies were included. Analysis showed that HIIT significantly reduced total, abdominal, and visceral fat mass. Results were the same in men and women. Between running and cycling HIIT, data suggested that the former may be more effective, but further research is needed (3).
Exercise in general is known to have a myriad of effects on the body, ranging from improved bone health to improved mental health. A broad meta-analysis sought to determine what different kinds of benefits HIIT specifically has. Researchers in the UK examined 33 systematic reviews in which participants were assigned to HIIT or a control group. Compared to active controls, who engaged in a different form of physical activity, HIIT subjects had improved cardiorespiratory fitness, muscle structure, and some markers of inflammation. Unsurprisingly, additional benefits were seen when compared to non-active controls – blood sugar and glycemic control, vascular health, heart rate, exercise capacity, muscle mass, and body measurements. HIIT was also associated with improvements in anxiety and depression (3).
Interestingly, one area in which HIIT does not seem to be better than standard moderate-intensity continuous training (MICT) is lipid profile. The aforementioned meta-analysis identified 12 relevant studies, but improvements in cholesterol and triglycerides were not generally seen (3). Another paper reported similar conclusions (1). However, because HIIT may also have the advantage of being more enjoyable than typical aerobic exercise, it has the advantage of inducing greater adherence.
High-intensity interval training has major benefits for many areas of health, including the heart, blood vessels, body composition, and mind. Those who are interested in adding HIIT to their routine can modify basic workouts that suit their needs and/or available resources.
References
- Wood, G., Murrell, A., van der Touw, T., & Smart, N. (2019). HIIT is not superior to MICT in altering blood lipids: a systematic review and meta-analysis. BMJ Open Sport & Exercise Medicine, 5(1), e000647. doi:10.1136/bmjsem-2019-000647
- Maillard, F., Pereira, B., & Boisseau, N. (2017). Effect of High-Intensity Interval Training on Total, Abdominal and Visceral Fat Mass: A Meta-Analysis. Sports Medicine, 48(2), 269–288. doi:10.1007/s40279-017-0807-y
- Martland, R., Mondelli, V., Gaughran, F., & Stubbs, B. (2019). Can high-intensity interval training improve physical and mental health outcomes? A meta-review of 33 systematic reviews across the lifespan. Journal of Sports Sciences, 1–40. doi:10.1080/02640414.2019.1706
- Tinsley, G., & Read, T. (2021). “7 Benefits of High Intensity Interval Training (HIIT).” Healthline. https://www.healthline.com/nutrition/benefits-of-hiit