High-intensity interval training is all the rage in fitness at the moment, but should you be doing it? While there are benefits, HIIT is certainly not the holy grail that it is being presented as. It is not for everyone—and, that’s O.K.
First off, let’s be clear, HIIT interval training is nothing new. It has been around for as long as exercisers have been doing “intervals”. By definition, HIIT is a form of interval training, an exercise strategy alternating short periods of intense anaerobic exercise with less-intense recovery periods. HIIT sessions can be quite short, usually last from 10–30 minutes. Despite the brevity, these are purported to improved aerobic capacity, improve glucose metabolism, and improved fat burning. Note that the only thing that distinguishes HIIT from other types of interval training is the intensity. Protocols vary, but high-intensity is pretty much anything over 85% of maximum (VO2max, heart rate max, etc.). Because the intensities are so high, they cannot be performed for very long (usually 20-seconds to one-minute intervals).
If you are going to a gym and doing cardio, you may have heard the name “Tabata”. Tabata has erroneously become almost synonymous with HIIT. The “Tabata Method” is based on a 1996 study by Izumi Tabata et al. that initially involved Olympic speed skaters. The study used 20 seconds of ultra-intense exercise (at an intensity of about 170% of VO2max) followed by 10 seconds of rest, repeated continuously for 4 minutes (8 cycles). The exercise was performed on a mechanically braked cycle ergometer. Tabata et al. called this the “IE1 protocol”.
In the original study, athletes using this method trained four times per week, plus another day of steady-state training (see below), and obtained gains similar to a group of athletes who did steady state training (70% VO2max) five times per week. The steady state group had a higher VO2max at the end (from 52 to 57 ml/kg/min), but the Tabata group had started lower and gained more overall (from 48 to 55 ml/kg/min). Also, only the Tabata group had gained anaerobic capacity benefits. It is important to note that in the original study from 1996, participants were disqualified if they could not keep a steady cycling pace of 85 RPM for the full 20 seconds of work—thus, if one cannot keep up with the prescribed intensity, they may not see the same results observed in the study.
Now, I don’t know about the reader, but the IE1 protocol is beyond tough. So, if your trainer is calling a workout “Tabata”, it is probably much less than this. Those <12-minute cardio sessions? They are probably not enough to elicit a significant cardiorespiratory adaptation—especially if they are made up of a series of body weight exercises (e.g., burpees). These have their place—primarily for calorie burn—but they are not likely to improve oxygen consumption.
HIIT—that is specific to the cardiorespiratory system—should be about 20-30 minutes of exercise with at least 8-16 minutes of high-intensity intervals, but this is my rule-of-thumb. There are no defined rules. Indeed, the whole notion of “HIIT” is a bit arbitrary. Key is the “HI”—high-intensity (>85% maximum)—and “IT”—interval training. In other words, high-intensity burst followed by recovery period; repeat.
HIIT gets all the glory, but let’s not forget about her little brother, “MIIT”. Moderate-intensity interval training is pretty much the same, but lower exercise intensity (~70-85% of maximum) intervals. These can be done for a longer exercise session and are a safer risk of injury.
If you prefer a less complicated—zone-out—kind of cardio, there is also “steady-state” cardiorespiratory exercise. Here, one typically doesn’t vary the intensity of the exercise. An example would be running 3 miles on a treadmill at 9 miles per hour. It is great for binge-watching Netflix and burning some kcals. It can also be more boring and time consuming.
Steady-state cardio can typically run the gamut of low-intensity (LISS) to moderate-intensity (MISS) depending on the intensity. In general, there will be an inverse relationship between time and intensity. Time versus intensity is really a matter of preference and “opportunity cost”.
The duration of a cardio session can be set based on a time or calorie goal. I often prefer to monitor calories over time when doing cardio (because my cardio goals are more closely tied to my body composition goals). I know that I am more likely to push a little longer to extend the calorie burn, whereas I will stop at a time goal. Whatever one prefers.
So, which type is best for you? That is for you to answer. It all depends on goals and opportunity. If you are looking to burn calories and are limited on time, HIIT is probably the way to go—at least a couple of sessions per week (more in a moment). If you have time and want to burn calories, then LISS might be best. If your goals are improving oxygen consumption and performance (e.g., running a 5-K), MISS might be preferable.
The folks at Renaissance Periodization have published a pretty good pros and cons comparison chart:
More than likely, you will want to mix it up little bit—especially if your goals are mixed. The most important thing is to do something. Secondly, whatever you do, do it well. If you are focused on building muscle, but want to live to show it off, I’d recommend HIIT a few sessions per week. If you want to run a marathon, you are going to need to include some LISS in there—and find some time to squeeze some weight training in there, as well.
Remember: opportunity costs. Manage your exercise time effectively. Don’t put effort (and time) into what does not further your goals. Time is precious. Use it wisely! Carpe momento!