What is high-intensity interval training?
If you have any interest in fitness at all then you will no doubt be aware of high-intensity interval training, HIIT for short. This style of training involves repeated vigorous-intensity efforts lasting from 30 seconds – 4 minutes separated by short periods of rest or active recovery. If you are not training for a particular event but are wanting to get fit and burn fat then HIIT is one of the most effective, time efficient and enjoyable methods to use. At the moment I am not competing in any events (apart from another obstacle race hopefully), however, I want to maintain fitness and maintain a healthy weight range. I have incorporated HIIT into my workouts to achieve these goals.
The benefits of HIIT are backed up by the research
My intuition has always told me that intensity trumps volume for improving fitness, and now the science clearly backs this up. Not only is high-intensity interval training superior for improvements in overall fitness compared to continuous moderate-intensity exercise, there are also numerous other health benefits associated with this type of training. There are countless articles in the scientific literature on the benefits of HIIT versus a more traditional moderate, aerobic based exercise protocol. As I began digging in to the literature, I discovered that actually HIIT was first described in 1960 by Astrand et al (1). It has more recently resurfaced as an effective method to improve cardiovascular function, endothelial function, muscle metabolic capacity and insulin sensitivity in a range of populations in all age groups (2, 3).
Let me name for you the titles of a few of the latest studies I came across and a brief summary of their findings.
Eight weeks of a combination of high-intensity interval training and conventional training reduce visceral adiposity and improve physical fitness: a group based intervention (4): While only a small group of 39 individuals participated in this study, the authors found that a combination of group based HIIT and conventional gym training over the course of 8 weeks was more effective at reducing total body fat and visceral adiposity or abdominal fat than conventional gym training alone.
High-Intensity Interval Training for Improving Postprandial Hyperglycemia (5): Postprandial hyperglycemia, meaning elevated blood sugar levels after eating a meal, is a risk factor for cardiovascular disease and mortality in patients with Type 2 diabetes. Even in patients without diabetes, elevated postprandial hyperglycemia is associated with future cardiovascular disease mortality. This recent review describes the results from a number of studies all reporting that HIIT leads to greater reductions in postprandial hyperglycemia when compared to moderate-intensity continuous exercise protocols.
Running sprint interval training induces fat loss in women (6): I thought this study was particularly relevant. Sprint interval training (SIT) is differentiated from high-intensity interval training by the effort exerted. Sprint interval training involves repeated 10 – 30 second “all-out” exercise efforts, whereas HIIT, as mentioned above, involves slightly longer bouts of vigorous-intensity exercise. Studies have shown that SIT results in training and performance adaptations similar to those of both HIIT and traditional endurance training, but with a reduced time commitment. In this particular study, 15 healthy, recreationally active women completed 6 weeks of running SIT consisting of 4 – 6 30 second running maximal efforts with 4 minutes of active recovery ie. walking, 3 times per week. The study found that the 6 weeks of running SIT decreased fat mass by 8%, decreased body fat percentage and decreased waist circumference by 3.5% and improved aerobic capacity and peak running speed in these women with no changes in diet. The results of this study are quite impressive considering the total training time was only 6 – 9 minutes per week!
Furthermore, according to the literature, not only is HIIT able to improve your physical health, but also your mental health. One study in particular looked at 47 women aged between 30 – 65 years at risk for developing Metabolic syndrome*, 23 of which engaged in a sprint interval training (SIT) protocol consisting of three sessions per week for 6 weeks of 4 – 8 30 second all-out cycling sprints followed by a 4 minute active recovery, while the remaining 24 in the study had no exercise intervention. This study found that those women who participated in the SIT protocol and who perceived their health as the worst in the group prior to commencement of the training protocol, reported improvements in role-physical scores, bodily pain, vitality, social functioning and mental health compared to the non-exercise control group. Role-physical scores improve when one feels that their physical health allows them to achieve more in their everyday life. Additionally, those women who participated in the SIT protocol and reported the worst mood states in the group prior to commencement of the training protocol, showed improvements in tension, depression, anger, vigor, fatigue, confusion and overall mood. In other words, those who felt the worst before participating in the SIT protocol reported the biggest gains in perceived health and mood (7).
Moreover, low bouts of HIIT can allow you to maintain improvements in vascular function gained by a conditioning exercise protocol once you have ceased this protocol (8).
And finally, you may find that you actually enjoy HIIT more than continuous moderate-intensity or continuous vigorous-intensity exercise and are more willing to stick to it. One interesting study involved 44 healthy participants who performed three different types of exercise spaced one week apart. These three types of exercise were 1. Continuous moderate-intensity exercise (CMI); 2. Continuous vigorous-intensity exercise (CVI); and 3. HIIT. All exercises were performed on an exercise bike. The CMI consisted of riding at approximately 40% of their maximum effort for 40 minutes, CVI consisted of riding at approximately 80% of their maximum effort for 20 minutes and the HIIT involved 20 minutes of riding alternating between 1-minute intervals at 100% of maximum effort and 1 minute recovery at 20% of their maximum effort. The researchers assessed the participant’s feelings towards each exercise type, confidence in their ability to repeat the exercise, intentions to engage in the exercise, enjoyment of the exercise and preference of each of the exercises. The results of the study revealed that HIIT was more enjoyable and the preferred exercise method compared to CVI and comparable to CMI. Moreover, participants reported feeling just as confident in their ability to perform HIIT as they did with CMI (9).
An example of a HIIT session – hill sprints
So I am sure I have convinced you of the benefits of HIIT over continuous moderate-intensity exercise. Personally, I think that if you want to really maximize your fitness, a combination of HIIT and continuous vigorous-intensity or tempo effort is required, but vigorous-intensity exercise is difficult to maintain and that is not the point of this blog post. An example of a high-intensity workout that I perform on a weekly basis is 10 hill sprints. I have a steep hill, which is approximately a 10 minute run away from my house. My workout consists of running easy to the hill as a warm up, completing 10 hard sprints (~80 – 90% of my maximum effort) up the hill, which takes between 1:05 – 1:15, depending on how I am feeling. I perform these 10 sprints on a 3 minute cycle. This gives my sufficient time to recover by running down the hill and having a short rest at the bottom until the 3 minute cycle is complete. I complete this workout with the run back home.
The workout I perform is one that you can build up to, but in the meantime, find a short, fairly steep hill in your area and try the beginner or intermediate versions. Please refer to the Disclaimer on the About me page before embarking on any exercise program.
6 x 30 second hill sprints at ~80% maximum effort on a 3 minute cycle
8 x 1 minute hill sprints at ~80 – 90% maximum effort on a 3 minute cycle
10 x 1 minute hill sprints at ~80 – 90% maximum effort on a 3 minute cycle
*Metabolic syndrome is a risk factor for cardiovascular disease and, according to the World Health Organization, is diagnosed by the presence of insulin resistance identified by Type 2 diabetes, impaired fasting glucose or impaired glucose tolerance, together with at least two of the following: hypertension (high blood pressure), hyperlipidemia (elevated levels of lipids – cholesterol and/or triglycerides), central obesity (abdominal fat) and microalbuminuria (the presence of albumin in urine (10).
- Astrand I, Astrand PO, Christensen EH, & Hedman R (1960) Intermittent muscular work. Acta physiologica Scandinavica 48:448-453.
- Gibala MJ, Little JP, Macdonald MJ, & Hawley JA (2012) Physiological adaptations to low-volume, high-intensity interval training in health and disease. The Journal of physiology 590(Pt 5):1077-1084.
- Weston KS, Wisloff U, & Coombes JS (2014) High-intensity interval training in patients with lifestyle-induced cardiometabolic disease: a systematic review and meta-analysis. British journal of sports medicine 48(16):1227-1234.
- Giannaki CD, Aphamis G, Sakkis P, & Hadjicharalambous M (2015) Eight weeks of a combination of high intensity interval training and conventional training reduce visceral adiposity and improve physical fitness: a group-based intervention. The Journal of sports medicine and physical fitness.
- Little JP & Francois ME (2014) High-intensity interval training for improving postprandial hyperglycemia. Research quarterly for exercise and sport 85(4):451-456.
- Hazell TJ, Hamilton CD, Olver TD, & Lemon PW (2014) Running sprint interval training induces fat loss in women. Applied physiology, nutrition, and metabolism = Physiologie appliquee, nutrition et metabolisme 39(8):944-950.
- Freese EC, et al. (2014) Effect of six weeks of sprint interval training on mood and perceived health in women at risk for metabolic syndrome. Journal of sport & exercise psychology 36(6):610-618.
- Weston M, Taylor KL, Batterham AM, & Hopkins WG (2014) Effects of low-volume high-intensity interval training (HIT) on fitness in adults: a meta-analysis of controlled and non-controlled trials. Sports medicine 44(7):1005-1017.
- Jung ME, Bourne JE, & Little JP (2014) Where does HIT fit? An examination of the affective response to high-intensity intervals in comparison to continuous moderate- and continuous vigorous-intensity exercise in the exercise intensity-affect continuum. PloS one 9(12):e114541.
- Grundy SM, et al. (2004) Definition of metabolic syndrome: Report of the National Heart, Lung, and Blood Institute/American Heart Association conference on scientific issues related to definition. Circulation 109(3):433-438.