WHAT IS HIIT?
With this issue of ACSM’s Health & Fitness Journal® themed around HIIT, there is no doubt you have already read at least one definition of what high-intensity interval training or “HIIT” is. Nonetheless, I feel compelled to begin this Nutritionist’s View article with a definition of HIIT. HIIT is a type of training where a person has bursts of high-intensity training, coupled with lower-intensity recovery periods. The idea behind HIIT training is that it combines high-intensity anaerobic training with lower-intensity aerobic training. There are many variations of HIIT training. Some of you reading this may already have been incorporating HIIT training for many years. When I think back to my early days of training in high school, our track coaches incorporated HIIT training at least twice a week, where we would run, for example, 10 by 200 or 400 meters, then have a slow jog for about 2 minutes in between each hard sprint. The type of workouts I do now also are HIIT training. Tabata training is another form of HIIT training, where it incorporates 20 seconds of high-intensity exercise with 10 seconds of rest or low-intensity exercise. Tabata workouts were created by Dr. Izumi Tabata, who researched the effects of interval training on cardiovascular fitness. In 1996, Tabata et al. (1) reported that although moderate-intensity exercise significantly increased aerobic power, Tabata training significantly increased both aerobic and anaerobic energy systems.
HIIT AND BODY COMPOSITION IN WOMEN AND MEN
HIIT research has varied among many populations. For this article, the focus will be on how HIIT affects body composition in individuals who are overweight and/or obese. Kong et al. (2) researched the effects of a HIIT program on various parameters, including body composition. Their participants were 18 women, 18 to 30 years of age, who were overweight and/or obese (average body mass index [BMI] = 25.5 ± 2.1 kg/m2; 36.7% ± 4.8% fat assessed by dual-energy X-ray absorptiometry) who were randomly assigned to complete HIIT or moderate-intensity continuous training (MICT) for 5 weeks. The HIIT consisted of 8 seconds of cycling on a cycle ergometer and 12 seconds of passive recovery for a total of 20 minutes (n = 10). Those in the MICT group cycled at 65% of their baseline (measured) peak oxygen consumption (V·O2peak) for 40 minutes (n = 8). Both groups exercised 4 days per week for 5 weeks. Although there were no significant improvements in body composition in either group, both groups significantly increased peak power output. The rating of perceived exertion was significantly greater in MICT compared with HIIT (P = 0.042), indicating that HIIT was not perceived as difficult among this group of women.
Chin et al. (3) researched the effects of different frequencies of HIIT compared with MICT on the body composition of 56 men, 18 to 30 years of age, who were obese (BMI = 26.4 ± 2.9 kg/m2). The men were randomly assigned to one of five groups: 1) control group (no intervention, n = 14); 2) MICT group, who exercised three times per week (n = 9); 3) HIIT group who exercised three times per week (n = 14); 4) HIIT group who exercised twice per week (n = 10); and 5) HIIT group who exercise once per week (n = 9). The MICT group ran continuously at 60% of their heart rate reserve for 30 minutes on a flat service, whereas the HIIT groups completed 30-meter shuttle runs. The HIIT sessions were performed at 90% of heart rate reserve (12 bouts at 1 minute) and included 11 bouts of active recovery for 1 minute at 70% of heart rate reserve. The entire intervention was 8 weeks in duration. Chin et al. (3) reported that aerobic capacity and percent of fat-free mass significantly increased, whereas body fat mass significantly decreased in all exercise groups compared with the control group (P < 0.05). They concluded that “low-frequency HIIT might be a feasible and effective strategy for the prescription of an initial exercise program for inactive, overweight, or obese young men” (3).
Miguet et al. (4) examined the effect of 16 weeks of HIIT or MICT on the body composition of 43 adolescents with obesity, who were randomly assigned to one of the two groups. They reported that although both groups had significant decreases in percent body fat, those in the HIIT group decreased percent body fat slightly more.
In a systematic review and meta-analyses, Sultana and colleagues (5) evaluated the effects of low-volume HIIT compared to MICT and a nonexercising control group on body composition in individuals who had a healthy body weight and who were overweight or obese. They included 47 studies in their analyses and reported that although low-volume HIIT significantly improved cardiorespiratory fitness compared with the MICT group (P = 0.017) and the nonexercise control group (P < 0.001), there were no differences in body composition changes among the groups. Nonetheless, they concluded that HIIT is an efficient way for people to improve cardiovascular fitness.
HIIT provides an efficient means of exercise. Although not all researchers have consistently demonstrated significant improvements in body composition with HIIT, the efficiency of HIIT may lead to greater adherence to being active over time. Including HIIT in everyone’s training and, in particular, in individuals who are overweight or obese may lead to greater fitness improvements and, over time, greater body composition improvements. In addition, HIIT will add variety to training that may also lead to greater adherence over time.
1. Tabata I, Nishimura K, Kouzaki M, et al. Effects of moderate-intensity endurance and high-intensity intermittent training on anaerobic capacity and V·O2max
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2. Kong Z, Sun S, Liu M, Shi Q. Short-term high-intensity interval training on body composition and blood glucose in overweight and obese young women. J Diabetes Res
3. Chin EC, Yu AP, Lai CW, et al. Low-frequency HIIT improves body composition and aerobic capacity in overweight men. Med Sci Sports Exerc
4. Miguet M, Fearnbach NS, Metz L, et al. Effect of HIIT versus MICT on body composition and energy intake in dietary restrained and unrestrained adolescents with obesity. Appl Physiol Nutr Metab
5. Sultana RN, Sabag A, Keating SE, Johnson NA. The effect of low-volume high-intensity interval training on body composition and cardiorespiratory fitness: a systematic review and meta-analysis. Sports Med
6. Machado AF, Baker JS, Figueira Junior AJ, Bocalini DS. High-intensity interval training using whole-body exercises: training recommendations and methodological overview. Clin Physiol Funct Imaging