(Credited to Marissa Gold) High Intensity Interval Training: What Is HIIT, And How Do You Know If You're Doing It?

The dos and don’ts for better results.

If you work out, or if you talk to people who work out, you should be familiar with high intensity interval training. You probably associate it with sweating, panting, and burpees
—lots of burpees. Beyond those basics, you know that it's intense, you do a variety of moves in intervals, and it's training. Name says it all, right?
Well, actually it doesn't. There's a lot more to high intensity interval training (hereafter referred to as HIIT) 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, or high-intensity training, without actually doing a real HIIT workout. There's also a lot of misinformation about HIIT out there that might lead you to believe that you're going to get the shredded results you want without putting in the necessary work. The truth is that HIIT can be an incredibly effective way to work out and see the body composition and fitness results you want, but you need to do it right. Good news: We're going to help you read between the letters. Here, fitness pros share the must-know HIIT facts so you can torch calories, burn fat, and build muscle effectively.
Intensity is key—obviously—which means you really have to work.
HIIT is a cardio session arranged as short bursts of very hard work. The whole point of high-intensity training is to kick up the intensity of your cardio. In order to qualify as true HIIT, you’ll need to push yourself to the max during every set. That’s why they’re short—anywhere from 20 to 90 seconds, typically. It’s the opposite of going for a long run where you ration your energy in order to sustain the activity for longer.
Numerous studies have shown that working your hardest is key when it comes to boosting endurance, increasing metabolism , regulating insulin levels, and losing body fat. “All exercise helps burn fat by burning calories,” says fitness expert and celebrity trainer Rob Sulaver. But, he adds, “more intense exercise burns more fat,” and that's part of the reason HIIT is so popular.
And compared to many other cardio
workouts , HIIT can be a more effective way of getting shredded, Sulaver explains. HIIT routines that involve bodyweight work (e.g. push-ups ) or added weight, such as kettlebells, medicine balls, or dumbbells, will tone your muscles while spiking your heart rate. “HIIT is effective on multiple fronts. It’ll improve your endurance, it will complement your strength development, and it’ll help you get shredded,” he says.
This level of intensity takes a little getting used to. To help gauge whether you’re working hard enough, fitness pros use a rate of perceived exertion (RPE) scale that describe effort levels on a spectrum of 1 to 10, with 10 being an all-out, balls-to-the-wall, 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),” says Franci Cohen, personal trainer and exercise physiologist.
Sound like a lot of work? That’s the idea: Working harder = higher oxygen intake = greater calorie burn. And HIIT will help you burn more calories both during and after your workout thanks to post-exercise exercise oxygen consumption, or EPOC. Studies have shown that high-intensity cardio —the kind that leaves you out of breath—raises your metabolic rate to the point where you continue to burn calories even after the session ends— as much as six to fifteen percent more. So for that 30, 60, or 90 seconds when you’re “on,” channel Rihanna and get to work.
Taking breaks to rest is also a defining element of HIIT.
What might not spring to mind when you think about high-intensity interval training? Rest . But here’s the drill with HIIT: Rest periods between each set are an essential part of the workout—if you don’t take time to recover, you’re not doing it properly.
Recovering before the next interval is essential, and here’s the reason why: Forcing your body to repeatedly acclimate between two very different states provides excellent cardio conditioning. “When the body works to adapt from the anaerobic (high-intensity) period to the low-intensity recovery period in HIIT, this workload results in high caloric expenditure, which can lead to fat loss,” explains Cohen.
“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.
Now that you know the basics, here’s how to make sure your workout is HIITing the right note.
“The rules of HIIT are pretty simple: work really hard, rest, then work really hard again,” says Sulaver. If you’re taking a group fitness class or
working out with a trainer , they’ll time your sets and rest periods and guide you as you go. But you absolutely don’t need a fancy gym, workout plan, or even any equipment at all—just find an activity that gets your heart rate up, and then apply the HIIT format to it.
A good place to start for beginners is with a 1:2 ratio of work to rest. So basically go all out on a chosen activity for, say, 30, 60, or 90 seconds, rest for twice as long, then start on the next set. (As you get better you can transition to a 1:1 ratio.) “Within those confines the possibilities are endless," Sulaver says. "You can sprint. You can use the assault bike. You can run stairs. It’s all technically HIIT, as long as it’s intense,” Sulaver says.
A typical HIIT session is about 20-45 minutes of working and resting. (Another popular workout similar to HIIT is Tabata training , where you are on for 20 seconds, off for 10 seconds, repeated for four minutes. If you want to try that routine, we've got all you need to know right here .)
Here are some SELF-approved at-home HIIT workouts you can try on your own: