This Is What You Really Need To Know About High Intensity Interval Training

If you work out, or if you even 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 burpeeslots 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.

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.

Here are some SELF-approved at-home HIIT workouts you can try on your own:

HIIT is a great workout, but it isn’t the only type of training you should be doing.

And in fact, too much is definitely not a good thing. Overkill will prevent you from working at your true maximum capacity during each session, explains Cohen, so don’t schedule a HIIT session every day of the week. A better approach? “Try HIIT three times per week with another two days of moderate cardio,” says Cohen.

And HIIT isn’t for everyone. If you’re training for a specific goal or race, you’ll want to follow the appropriate training program—and HIIT may or may not be a part of that plan. Due to the intensity level involved, you should always check in with your doctor before starting HIIT, as with any exercise program.

One last piece of advice: If weight loss is a goal, the old saying that you can’t out-train a bad diet is true, even if your workouts are super demanding. HIIT isn’t an excuse to neglect your diet, so experts stress to keep it clean, calculate your daily calorie needs, and plan your carbs (read: energy!) around your workouts. When you incorporate effective HIIT training into your exercise regimen and keep your diet in check, that’s when you can really see results.

Now you’re primed and ready to get the most out of your next HIIT session. Just remember this mantra: If you’re not working your hardest, you’re not doing HIIT.

SELF – Fitness