If you work out, or if you talk to people who work out, you're most definitely familiar with high-intensity interval training (HIIT), and you probably associate it with sweating, panting, and burpees—lots of burpees. It's intense, you do various moves at intervals, and it's training. Name says it all, right?
Well, actually, it doesn't. There's a lot more to HIIT than its name alone suggests. 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.
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.