One of the most commonly stated New Year’s Resolutions is losing some extra pounds, starting a jogging routine, or otherwise getting physically fit. It is a very noble goal with good intentions, but many people who make this resolution for the new year end up breaking this promise to themselves. Chief among the reasons for quitting is the lack of time during the day. Between work, school, family, friends, and other obligations, it can be hard to set aside one or two hours to do a full traditional workout routine. But what if there were a way to get some exercise in regardless? What if you could work out for as little as 7 minutes, and get the same results as if you worked the full hour? As long as you follow a specific type of workout, this dream could be a reality. Enter: High-intensity interval training.

Figure 1: A Warrior Training instructor, leading her class.

By Any Other Name:

High-intensity interval training (HIIT) takes many different forms and names: Tabata Training, Sprint Interval Training, 7 Minute Workouts, and Warrior Training are all different forms of HIIT. The core idea behind HIIT is that athletes who take part of these programs work at maximum exertion for a short period of time before taking a short break. According to the guidelines put forth in the ACSM’s Health & Fitness Journal [2], working at a maximal output for short bursts of time causes you to generate close to 90% of your VO2 Max (also known as a VO2 Peak) over the course of the exercise. These guidelines, which have formed the basis of the 7 Minute Workout, pen the program as a time-efficient way to get similar efforts to other workouts that last longer, by trading time for increased effort. But how true is this claim? Can you really get the same workout you would in an hour in the span of 7 minutes, simply by working at maximal output? This is the question, one that I hope to answer.

Insulin Activity:

One study [3] focused on the potential for Sprint Interval Training (SIT) to be used for promoting insulin sensitivity, as well as other indicators for increased cardiometabolic health. In this study, they took 27 sedentary men with similar age, weight, and VO2 Peak. These men were divided into three groups and were given different workout routines: one was SIT, one was a traditional moderate-intensity continuous training (MICT), and the last did not train at all as a control. The SIT group would do high intensity, 10-minute sessions, while the MICT group would do more moderate bouts over 50 minutes sessions. Over the span of 12 weeks, these men worked out and got measurements of their results. They concluded that SIT was comparable to MICT, with regards to improving VO2 Peak, insulin sensitivity, and skeletal muscle adaptations. The study does not, however, make any mention of weight loss, though that is due to it being outside of their scope.

Figure 2: VO2 Peaks of the different groups in the study before, in the middle of, and after the full study.

New Year’s Resolution Buster:

In regards to body fat, one review [4], though dismayed at the effort required to adhere to the HIIT program, found it to be a preferable alternative to MICT. In that review, not only did they find many of the same adaptations from the study above, they found that many studies point out increased levels of skeletal muscle fat oxidation using HIIT. Another study [5] found that HIIT, while better than sedentary activity, was not significantly better than MICT, and may even be slightly worse. Still another study review [6] suggests that HIIT and MICT have similar benefits, with the only difference between the two being time.

One term that gets thrown out a lot during discussions is EPOC or Excess Post-Exercise Oxygen Consumption. Long name aside, it is a process that your body undergoes after exercising in order to bring the body back to a normal state. In this recovery state, the body uses more energy and calories compared to your resting rate as it tries to help heal and build your muscles. This gets thrown around especially in regards to HIIT, as some review articles [6] report that HIIT can lead to increased levels of EPOC, compared to MICT. This sounds like a decisive point in HIIT’s favor, as calorie burn is often the biggest signifier of hard work for starting athletes. But the actual amount of calories that are burned as a result of EPOC, according to this review [7] might not be very substantial in the first place.

The Bottom Line:

Armed with all of this information, what can we say about HIIT? As a form of exercise, it seems to be a perfectly valid way of working out. Whether it is better or worse than traditional duration exercises is up for debate, but HIIT is at least around as good as MICT. Both MICT and HIIT cause similar increases in VO2 Max and other adaptations such as increased insulin sensitivity. Neither method has been shown to be significantly better at burning calories, either.

That being said, one common theme appears across several studies is how harsh the workout is. In almost every single review study involving HIIT, the discussion often concedes that HIIT is very intense and that not everyone will be able to maintain the level of exertion requested by HIIT. With this, I can say that HIIT will not be replacing MICT. Ultimately, the question of whether to do MICT or HIIT comes down to personal preference. If you don’t have time during your day and are willing to really sweat it out for a short amount of time, then HIIT is a good alternative choice. If you do have time during the day and don’t want to work out to near your maximal output, then stick with a more traditional workout may be the right thing for you.

Questions To Consider:

• Given a choice between working out using the HIIT method or the traditional MICT method, which would you choose?
• Would you recommend HIIT to a beginner athlete?
• What about someone more grounded in their routine? Would you ask them to give it a shot?
• Looking through a calories-down lens, would you focus on HIIT?
• If you are working out using the traditional MICT method, would you integrate some HIIT workouts in there as well?
• Given the short time investment, would you work out using HIIT 7 days a week?

[1]: Figure 1: Warrior Trained Fitness offers service members, families’ group workout. https://www.nellis.af.mil/News/Article/665186/warrior-trained-fitness-offers-service-members-families-group-workout/.

[2]: Klika B, Jordan C. HIGH-INTENSITY CIRCUIT TRAINING USING BODY WEIGHT. ACSMs Health Fit J. 2015;17(3):8-13. doi:10.1249/fit.0b013e31828cb1e8

[3]: Skelly LE, Martin BJ, Gibala MJ, Gillen JB, MacInnis MJ, Tarnopolsky MA. Twelve Weeks of Sprint Interval Training Improves Indices of Cardiometabolic Health Similar to Traditional Endurance Training despite a Five-Fold Lower Exercise Volume and Time Commitment. Sandbakk Ø, ed. PLoS One. 2016;11(4):e0154075. doi:10.1371/journal.pone.0154075

[4]: Boutcher SH. High-intensity intermittent exercise and fat loss. J Obes. 2011;2011:868305. doi:10.1155/2011/868305

[5]: Keating SE, Johnson NA, Mielke GI, Coombes JS. A systematic review and meta-analysis of interval training versus moderate-intensity continuous training on body adiposity. Obes Rev. 2017;18(8):943-964. doi:10.1111/obr.12536

[6]: Børsheim E, Bahr R. Effect of Exercise Intensity, Duration and Mode on Post-Exercise Oxygen Consumption. Sport Med. 2003;33(14):1037-1060. doi:10.2165/00007256-200333140-00002

[7]: Laforgia J, Withers RT, Gore CJ. Effects of exercise intensity and duration on the excess post-exercise oxygen consumption. J Sports Sci. 2006;24(12):1247-1264. doi:10.1080/02640410600552064