HIIT: The benefits of exercise “in a shot”

According to the American College of Sports Medicine’s Global Fitness Trends 2019 survey, high-intensity interval training (HIIT) was seen as the top trend in exercise from 2014 to 2018¹. High-intensity interval training (HIIT), which features short periods of high-intensity exercise (at 80 to 95 % of your maximum heart rate ) interspersed with periods of passive or active recovery at low intensity (40 to 50 % of your maximum heart rate) induces significant cardiometabolic health benefits in healthy and clinical populations with less time commitment (Gillen and Gibala 2018)². In other words, HIIT is a time-efficient strategy for improving:

1. aerobic capacity (Kessler et al. 2012)
2. insulin sensitivity (Jelleymanet al. 2015)
3. blood pressure (Kessler et al. 2012)
4. body composition (Batacan et al. 2017)

HIIT compared to traditional resistance training or moderate intensity continuous training (MICT) can produce similar and even superior changes in physiological and physical performance and health, but with sustainably reduced exercise duration and volume^1,2.

The current physical activity recommendation suggests that accumulating 150 minutes of moderate-intensity physical activity or 75 minutes of vigorous-intensity physical activity per week could provide various benefits for cardiorespiratory, metabolic, and musculoskeletal health. This suggestion suggests that half the time of engaging in vigorous-intensity physical activity is required to have beneficial effects compared to moderate-intensity exercise.

Another recent study demonstrated the increased benefits of HIIT on cardiorespiratory health (ie, increased aerobic capacity and reduced blood pressure) and metabolic health (ie, reduced body fat)². Interestingly, this study further found that even a 23-minute HIIT session could provide the same positive cardiometabolic adaptations seen in moderate-intensity continuous MICT training². Specifically, just one HIIT session per week was enough to produce significant improvements in aerobic fitness, body composition, and blood pressure in overweight or obese young adults. Such a finding may give life to a new time-efficient and practical exercise strategy to improve cardiorespiratory fitness and reduce the risk of cardiovascular disease and related mortality.

The minimum weekly time commitment to HIIT comes in a new perspective and contrasts with the American College of Sports Medicine’s resistance training and interval training guidelines, according to which exercise less than 2 times/week can does not result in a significant improvement in cardiorespiratory fitness.

In addition, low-frequency HIIT showed a faster rate of improvement in cardiovascular fitness and a reduction in body fat². Therefore, low-frequency HIIT may be a practical approach for inactive and overweight individuals to initiate exercise.

Meta-analyses have found that short low-volume HIIT programs are as effective as prolonged high-volume HIIT programs regardless of baseline cardiorespiratory fitness or body weight³. For adolescents, low-volume HIIT during the school year, integrated into standard physical education classes in schools, could be an effective method to improve cardiorespiratory health without interfering with or consuming significant time from teaching and pedagogy course tactics.

In another study comparing HIIT in a real-world setting (running) with MICT, most of the positive effects of HIIT were also found to be longer lasting and maintained after training was suspended for 4 weeks¹. In contrast, all the positive effects of MICT were reversed after training was stopped. More specifically:

• 8 weeks of high-intensity interval running training, compared to continuous moderate-intensity training, was found to promote a greater number of positive adaptations in cardiometabolic health in overweight/obese men.
• The superior benefit of HIIT compared to MICT required less commitment time and exercise volume.
• Most of the positive effects of the HIIT protocol were maintained after 4 weeks without exercise.

The adaptations induced after HIIT can be particularly beneficial in situations where training needs to be reduced or stopped, such as when there are changes in work schedule or travel or student exam periods.

1. Chin EC, Yu AP, Lai CW, Fong DY, Chan DK, Wong SH, Sun F, Ngai HH, Yung PSH, Siu PM. Low-Frequency HIIT Improves Body Composition and Aerobic Capacity in Overweight Men. Med Sci Sports Exerc. 2020 Jan;52(1):56-66. doi: 10.1249/MSS.0000000000002097. PMID: 31343521.
2. Gripp F, Nava RC, Cassilhas RC, Esteves EA, Magalhães COD, Dias-Peixoto MF, de Castro Magalhães F, Amorim FT. HIIT is superior than MICT on cardiometabolic health during training and detraining. Eur J Appl Physiol. 2021 Jan;121(1):159-172. doi: 10.1007/s00421-020-04502-6. Epub 2020 Sep 30. PMID: 33000332.
3. Martin-Smith R, Cox A, Buchan DS, Baker JS, Grace F, Sculthorpe N. High Intensity Interval Training (HIIT) Improves Cardiorespiratory Fitness (CRF) in Healthy, Overweight and Obese Adolescents: A Systematic Review and Meta-Analysis of Controlled Studies. International Journal of Environmental Research and Public Health. 2020; 17(8):2955. https://doi.org/10.3390/ijerph17082955

ΑΓΓΕΛΙΚΗ ΦΩΤΕΙΝΟΥ