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Whatever your exercise of choice may be, chances are pretty good you’ve heard of the term high intensity interval training, or HIIT. But what is HIIT really, and how can you use it to make the most out of your workouts?
It’s a common—and legit question—whether you’re a fan of cardio like running or indoor cycling, or prefer to lift weights or strength train. While you might not know exactly what HIIT is, you may have an idea in your mind about what it entails. Burpees, anyone?
But like many workout protocols in the fitness field, there are some misconceptions about what HIIT really is, and what it can do for your fitness routine. Here’s what you need to know about this popular type of training.
What is HIIT?
There's a lot more to high intensity interval training than its name alone suggests. In fact, HIIT refers to a very specific and particular type of training—and it's possible to do interval training without actually doing a real HIIT workout.
The hallmark of HIIT is repeated, extremely hard bouts of work interspersed with periods of recovery. During your work intervals, you’ll be challenging yourself nearly to your max, Noam Tamir, C.S.C.S., founder and CEO of TS Fitness in New York City, tells SELF.
It’s the opposite of going for a long, easy run where you ration your energy in order to sustain the activity for longer. And it’s a little different from what you probably have seen labeled as “HIIT” in gen-pop exercise classes, says Tamir. Most protocols called “HIIT” would actually be more accurately described as circuit training or interval training, he says.
When your body is going all-out during true HIIT, it relies on your anaerobic pathways (breaking down glucose without oxygen) to produce the energy it needs to fuel you. This provides an immediate supply of energy, but the amount is very limited—which means the length of time you can sustain that max effort is quite short, says Tamir.
In fact, in true HIIT, you’d likely limit your work intervals to about 20 seconds, he says. Then you’d give yourself ample recovery time, usually at about a 2:1 or 3:1 ratio of rest to work. So if you were doing 20-second sprints, you’d rest for 40 seconds to one minute before beginning your next interval. (This is different from what many people call HIIT, where their work periods are way longer and rest periods much shorter, meaning they can’t go as all-out.)
Recovering before the next interval is essential: Forcing your body to repeatedly acclimate between two very different states provides excellent cardio conditioning, Franci Cohen, M.S., personal trainer and exercise physiologist, tells SELF. “The rest periods are needed to prep the body and enable it to truly perform at its max during the high-intensity spurts,” she adds.
As for how to determine whether you’re working at that near-max level? To help gauge whether you’re working hard enough, fitness pros use a rate of perceived exertion (RPE) scale that describes effort levels on a spectrum of 1 to 10, with 10 being an all-out, giving-it-everything-you-didn’t-think-you-had level of intensity. “Work intervals during a HIIT session should be at near maximum (e.g. 9),” Cohen says.
What are the benefits of HIIT?
The benefits of true HIIT are performance-based, especially for those looking to improve at a certain sport: “It’s really for athletes,” says Tamir. “With true HIIT, you’ll maximize your explosive performance and speed.”
There are other benefits too, including increases in VO2 max (how much oxygen you can use during exercise) and improvements in insulin sensitivity (how responsive your cells are to insulin), blood pressure, and cardiovascular function, according to a 2017 review published in the journal Sports Medicine.
While true HIIT might look a little different from the HIIT you’re used to doing, you’ll still reap many similar benefits from that modified HIIT. With longer work intervals—even if they aren’t at your max work—you’ll still get some good cardiovascular benefits, as well as improvements in strength and muscle endurance, Tamir says.
Because HIIT spikes your heart rate during those hard efforts, it can also help contribute to weight loss (if that’s your goal), since you’ll be burning more calories per minute than you would with lower-intensity work, says Tamir. This also makes it a convenient form of exercise for those who are short on time.
What workouts work with HIIT?
You’re probably most familiar with HIIT as a cardio workout, and it’s true that it does lend itself well to cardio-based sprints, whether you’re running, on a bike, or on a rower.
But you can use HIIT in strength-based workouts too. HIIT routines that involve bodyweight work or added weight, such as kettlebells, medicine balls, or dumbbells, will work your muscles while spiking your heart rate, fitness expert and celebrity trainer Rob Sulaver tells SELF.
Just make sure you choose exercises that allow you to be explosive, says Tamir—think push-ups, squats, or kettle-bell swings, rather than moves like bench press or lat pull-downs. (If you’re looking for some workout ideas, you can try this HIIT leg workout or a full-body HIIT kettlebell routine.)
What are some mistakes or safety issues to avoid?
Speaking of exercise choice, one mistake Tamir sees a lot is people trying to go all-out on moves when they don’t have the form down.
“The safer movements are going to be more bodyweight movements,” says Tamir. “When you add weight, technique is really important. If you’re going all-out and your form is off, you can put a lot of pressure on certain muscles and joints, which can lead to injury.” That’s why it’s important to make sure you can do an exercise with proper form at an easy tempo before kicking it up to high intensity.
A proper warm-up is also crucial, whether you’ll be doing cardio-based HIIT or strength-based HIIT. This should include mobility moves, like hip-opening stretches and thoracic spine rotations, as well as slower-tempo reps of the exercise you intend to use for HIIT, such as squats.
“The more intense the workout, the more important the warm-up is,” Tamir says. “It’s kind of like prepping your nervous system as well. If your body is not ready for that work, the outcome could be injury, or your performance can suffer.”
Scheduling a long HIIT session is also a mistake when talking about true HIIT—when you’re going all-out, you’re not going to be able to sustain that for a 45-minute class, he says. Instead, a true HIIT workout would look something like this: eight all-out, 20-second sprints, with one minute of rest in between. That means your HIIT protocol (not counting warm-up and cool-down) would be just over 10 minutes.
Which brings us to our last mistake: There’s nothing that says you need to do traditional HIIT if you want to do some hard-working interval training. In fact, according to Tamir, the modified HIIT we often see in classes—and what Tamir uses for some of his group sessions—is probably going to be more accessible and the better choice for the general exerciser.
And whether you’re doing true HIIT or modified interval training, don’t underestimate the importance of recovery: Prioritizing frequent, intense workouts while neglecting rest days can not only lead to diminishing performance returns with your fitness, but can also leave you open to injury, fatigue, or burnout, as SELF recently reported. Limit your HIIT to one or two workouts a week, and make sure you’re balancing them with plenty of easy workouts—as well as at least one straight recovery day per week.
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