By Andrew Taylor and Kathleen Wright
Figure 1. Women participate in a HIIT class.
How many of us have said we would go to the gym, only to realize later that we don’t have the time? High-intensity interval training (HIIT) classes have increased in popularity over the last few years, partly because the sessions are shorter than traditional workouts. HIIT workouts alternate short (20 or 30 second) intervals of maximum exertion with periods of rest or low-intensity exercises. Elite athletes might take part in HIIT to improve their aerobic energy metabolism and performance. If you have ever played a demanding sport, you have probably been subjected to HIIT during the game or practice. The recent obsession with HIIT raises the question: is it just a fad, or will it stick around as an effective means of exercise?
HIIT can be defined as brief exercise that generates a VO2peak, or 90% of the maximum VO2 potential, commonly followed by a relaxation period. This study utilized the Wingate test: participants repeated 30 seconds all-out maximal cycling on a specialized ergometer, with 4 minutes of recovery in between, for a total of 2 to 3 minutes of intense exercise. The authors focused on specific markers in skeletal muscle metabolic control; they determined an increase in skeletal muscle oxidative capacity after 2 weeks of HIIT. They also found that changes in carbohydrate metabolism (Figure 2) were comparable to adaptations from endurance training. Although exercise performance improved, there was no measurable change in participants’ VO2peak after 2 weeks of HIIT. However, this study did not fully investigate how HIIT affects the cardiovascular and respiratory systems, or metabolic control in other organs.
Figure 2. Results depict the glycogen content, or resting carbohydrate dry weight, found in skeletal muscle during rest and 20 minutes after exercise, both before and after 2 weeks of HIIT.
Additional HIIT data concerning VO2peak and citrate synthase activity support the previous claim that HIIT provides similar benefits to endurance training. This review recognizes that Wingate-based training may not be tolerable for everyone, and instead tested low-volume HIIT. The authors found that their model was time-efficient and effective in producing cardiovascular and skeletal muscle adaptations. They reference the results of similar studies, saying that HIIT is superior to moderate-intensity continuous training (MICT) in increasing cardiorespiratory fitness and endothelial function. However, researchers still don’t know what intensity or training volume is required to be effective.
A study concerning overweight and obese adults found that HIIT had similar results to MICT, in terms of body composition measures, but HIIT required less training time. They concluded that HIIT may be a time-efficient way to manage weight. Meanwhile, this systematic review determined that MICT and HIIT provide similar benefits for body fat reduction, but HIIT was no more time-efficient than MICT.
The data from these studies indicate that HIIT is comparable to MICT, similar to the difference between traditional and functional workouts, as described previously in this post. High intensity workouts can be very demanding, as seen with the Wingate test, and may not be suitable for all individuals. HIIT should not be substituted for specialized athletic training, but can be beneficial for athletes who need to quickly use their bodily carbohydrates. Many HIIT studies are short-term, like the first study we mentioned, and further research needs to be conducted to determine the long-term effects of HIIT on cardiovascular and respiratory systems. Although HIIT attracts people with the allure of getting fit fast, there isn’t enough data currently to support that HIIT is actually more time-efficient than endurance training.
Questions to Consider:
Should HIIT workouts be recommended for the average person?
Why could an increase in glycogen dry weight be considered important for exercise?
How could your current workout routine benefit from HIIT?
What athletes do you feel would benefit most from HIIT?
Recommended Further Reading- Works Cited
- Figure 1. HiiT_40-20_6108. Attribution: Cathe Friedrich. https://www.flickr.com/photos/cathefriedrich/albums/72157622565339997 [CC BY-NC-ND 2.0 (https://creativecommons.org/licenses/by-nc-nd/2.0/)]
- Gibala, M. J., & McGee, S. L. (2008). Metabolic adaptations to short-term high-intensity interval training: A little pain for a lot of gain? Exercise and Sport Sciences Reviews, 36(2), 58-63. 10.1097/JES.0b013e318168ec1f
- Gibala, M. J., Little, J. P., MacDonald, M. J., & Hawley, J. A. (2012). Physiological adaptations to low-volume, high-intensity interval training in health and disease. The Journal of Physiology, 590(5), 1077-1084. 10.1113/jphysiol.2011.224725
- Wewege, M., van den Berg, R., Ward, R. E., & Keech, A. (2017). The effects of high-intensity interval training vs. moderate-intensity continuous training on body composition in overweight and obese adults: A systematic review and meta-analysis. Obesity Reviews, 18(6), 635-646. 10.1111/obr.12532
- Keating, S. E., Johnson, N. A., Mielke, G. I., & Coombes, J. S. (2017). A systematic review and meta-analysis of interval training versus moderate intensity continuous training on body adiposity. Obesity Reviews, 18, 943-964. 10.1111/obr.12536
Yeah HIIT seems like a decent idea. If you warm up before engaging in HIIT, performing these high intensity workouts will place a high demand on your body, which will cause your body to adapt to this demand over time. HIIT seems alright if you’re training for sprints, but it doesn’t prepare you for anything longer than that in my opinion.
Anyway, I noticed in the HIIT workouts link that it says HIIT is excellent for losing body fat. I thought Professor Price from BMEG301 said low intensity workouts (walking) burns body fat. Does HIIT burn body fat at a lower rate then, or am I missing something here?
Jeremy, I have done additional research and updated the post, if you’d like to check it out. I don’t think that body fat is burned at a lower rate in HIIT. I found a systemic review that determined HIIT to be as effective as moderate-intensity training in body fat reduction.
Although HIIT seems like a promising exercise for increasing cardiac output and improving aerobic metabolism, I wonder what the rate of injury is for this type of intense workout. I’m not sure if I would recommend HIIT for novice athletes or the average person without first easing into working out with a less stressful type of exercise. With such short bursts of high-intensity exercises, it seems like an ideal situation for a pulled or strained muscle without the experience to know how to properly warm up and prevent injury.
Thanks for your insight Margot. I agree that HIIT can be risky, especially for beginners. I don’t know the statistics on injuries, but I tried a HIIT class once myself, and was not at all prepared. The instructor led everyone in stretches at the beginning and end of the class to reduce the risk of injuries, and offered suggestions throughout to modify the exercises (to make them easier in my case). So even though it’s certainly possible to get hurt, the instructors really do try to prevent that.
I think HITT seems really good for people who just want to get in better shape (versus training for a specific sport). But I agree with Margot about the risk for injuries. I read an article a while ago that mentioned improper form with these exercises as a large risk factor for injury. But besides that, all the results look promising. It it good for building muscle or just losing weight?
Hey Laura, I added a bit to the original post if you want to check it out. But the first study focused on muscle and found increased metabolic control in skeletal muscle, as well as a reduced rate of glycogen utilization and lactate production. It’s unclear whether HIIT is better for losing weight. One study found that the results are similar, but it’s more time-efficient. The last study, that I just added, concluded that HIIT is comparable to endurance training in terms of losing weight.
I believe that HIIT is a awesome component to work out but should not be the entire work out. To gear it more towards to average person you could have bursts of maximal effort followed by light weight strength training. Did you look at Tabata at all in your research? It is 20 seconds of maximum work and 10 seconds of rest for about 4 minutes followed by a minute of active recovery. I think something like this could be integrated into a HIIT routine followed by some low weight high repetition strength training. I believe this would help the average person benefit most from this type of work out and this changing between all out work and strength training could reduce some of the previously mentioned concerns for injury.
I believe any athlete that participates in an explosive sport would benefit from this type of training, the idea of HIIT or Tabtata would allow them to train their bodies to respond to a signal, explode into a short duration of all out work and then recover quickly.