What Is HIIT and Why You Should Be Doing It

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You might have heard the buzz about HIIT workouts, and how it’s all the rage. But what is it, exactly?

What does HIIT look like?

Intervals.

HIIT stands for High Intensity Interval Training. Let’s start with “interval training.” Interval training is a type of workout structure where you have set periods of time—intervals— where you change the exercise somehow. You might do a different exercise, do the same exercise but with different intensity, or go from rest to work or work to rest. Interval runs, for instance, usually involve going faster and slower at set intervals. Alternatively, if you were on a treadmill you could amp up the incline.

Intensity

Now for the “high intensity” part, this means you generally go all out during the work portion. You don’t rest unless you need to, and if you do rest, it’s as little as possible. Ideally, you figure out a speed or intensity or exercise that you can keep up for the entire interval.

I started with HIIT when I found a site online with Zuzka Light called Bodyrock. FYI, the current Bodyrock is her ex-husband’s business now, and Zuzka has her own enterprise at ZuzkaLight.com. Most of her workouts are through a paid subscription service, with which I’m not familiar. Knowing Zuzka, her style, her charm and the quality of her workouts, I would recommend at least checking it out. She should have some free workouts online, and you can still snag some old Bodyrock/Warriorz workouts here and there. She’s really easy to fall in love with, and her body is…wowza.

Most of those workouts were 10-15 minutes, and a common structure was 10&50×12, or 10 seconds rest, 50 seconds work, for 12 rounds. Another popular HIIT workout is Men’s Health Magazine’s Spartacus Workout, which is 15&60×10, three times with a 2-minute break The workout is great, but please, don’t follow the diagram for a single dumbbell swing! Follow Marianne’s tutorial video here instead. Even better, in my opinion, is the Spartacus 2.0. 2.0 has a structure of 20&40×10, four times with a 2-minute break between rounds. (I’m having trouble finding a working link of Spartacus 2.0 at the moment.)

Benefits of HIIT.

As long as you know how to do HIIT correctly, you’ll reap enormous benefits, such as:

1. It burns a lot of calories, i.e., fat.

That intensity pays off. Research is now showing that HIIT is more effective, and certainly more efficient, at burning fat than steady state cardio.

2. HIIT is best for burning visceral fat.

There’s fat beneath the surface of the skin, but there’s also fat in between all your organs. Having a lot of visceral fat, sometimes called belly fat, can come with health risks. HIIT is the most effective at burning this type of fat.

3. HIIT reigns queen of the afterburn effect.

Most exercise has an afterburn effect, meaning that it continues to burn calories after the workout is over. Strength training generally has a longer afterburn than basic, steady state moderate cardio. But HIIT has a killer afterburn that lasts almost 24 hours after the workout is over.

4. You won’t ever get bulky. But you will be able to maintain lean muscle.

If you’re looking to specifically build strength or large muscles, HIIT isn’t the best way to do it. For many women, though, this might be a plus. Even though women don’t really get “bulky” from strength training, you’ll be absolutely certain to keep muscle growth to a minimum with HIIT. For whatever it’s worth, anecdotal evidence of my own and my fellow fitness friends supports this. However, you are still stimulating the muscles, so if you don’t have much muscle, you’ll be sure to build some. If you have a little, you’ll help maintain what you have. And the extra fat you’re burning will help show off that muscle tone, giving you a more lithe, lean look.

5. HIIT helps keep you spry.

HIIT increases your fast-twitch muscle fibers. These are the fibers that help perform explosive, fast movement. As we age, we tend to lose these fibers forever unless we work them.

6. You’ll improve your aerobic fitness.

You’ll likely be gasping for air and your heart will be pumping hard, which keeps your cardiovascular system healthy and happy.

7. You’ll prevent or help treat diabetes.

This study at the University of Turku found that after only six HIIT training sessions, the glucose metabolism in the thigh muscles of insulin resistant subjects (type 2 diabetics or prediabetics) had increased to reach the same level as that of healthy subjects. And while moderate intensity training did also improve glucose metabolism, it was significantly lower than those who did HIIT training.

8. More workout in much, MUCH less time.

Who doesn’t have 10 or 15 minutes in a day? HIIT has shown to be as effective as a workout of continuous moderate intensity that is five times longer. That means that an intense workout of 10 minutes is the same as a moderate one of 50 minutes. Whoa.

9. Your workout is also done in a specific amount of time, so you can plan around it easier.

This is a benefit that’s an offshoot of the one above, but it’s beneficial enough to mention it on its own. If you have one of those schedules that’s back-to-back activities and obligations, you just need to find a block of time of 15-30 minutes to work out. It’s perfect for morning workouts, as you don’t have to wake up an hour and a half early; just get up 15 minutes earlier, which won’t make you any sleepier than you already are, strap those shoes on and get to it in 10 minutes.

Since you start at a specific time, you know you’ll be done at a specific time in order to take a shower, make breakfast, get the kids up, get to work, etc. Or, if you have a small block in the middle of your day, make sure you don’t fall into a social media rabbit hole and work out. It’s more conducive to having a meaningful workout during a lunch hour, so that by the time you get to the gym, change, put your stuff in your locker and fill your bottle, you can have a good workout with enough time to shower and get back.

10. HIIT gives you a natural high.

As intensity releases endorphins, and HIIT has bucketloads of intensity, HIIT releases bucketloads of endorphins. Endorphins are what give you that high after you work out (like runners’ high), making you feel great and solidifying your motivation to keep on keepin’ on.

But HIIT has its limits.

You can have too much of a good thing with HIIT. The problem with high intensity training is that it actually can become addictive. You know those endorphins I mentioned above? You can get addicted to them. And by “addicted,” I don’t mean you’ll be addicted like you would be to cigarettes or heroine.

However, missing a workout or doing a less intense one might make you feel like something’s missing, or like you’re failing in some way, merely because you’re not getting the same mood boost. The real danger comes in once you become accustomed to the intensity of the short HIIT workout and you feel like need more to get the same fix. If you keep increasing your intensity and/or the workout length to reach the same level of workout “enoughness” each time, it will lead to overuse of your muscles and joints, and exhaustion of your central nervous system.

You’ll get tired and maybe achey, and if you’re anything like me, you’ll still cling on to a manic need to do your workouts and resist rest. Don’t. You need rest.

I started out doing Zuzka’s 12-minute workouts and believe it or not, they were enough.

For a while.

But then your body gets used to 12 minutes, so you do two HIIT workouts back-to-back. Or three. Or you do one after your evening run, because you need that fix.

Motivation vs. obsession.

Note how you feel. Take notes if you need to. Being compelled to work out is mostly a good thing, and the mood boost you get is literally the most important benefit (in my humble opinion) of exercising. It keeps you motivated and feeling great. Just be sure to keep your workout in healthy balance with the rest of your life and your physical needs, and know when your motivation turns into obsession.

In general, I recommend doing no more than two or three HIIT workouts a week. However, I often break that rule. If you’re doing it five times a week, then balance it out. Or cut some workouts short, or change up the format. You can still do Metabolic Resistance Training without intervals—just adjust the workout to a set amount of reps instead of using the interval timer. While you could technically do it at the same intensity as you would with intervals, you probably won’t. Having the timer there really pushes us psychologically to go above and beyond, so with a regular circuit, you’ll likely reduce the intensity naturally.

HIIT is just one form of MRT. You can find many more workout structures here.

Rest periods.

If you’re doing HIIT a lot, be sure to rest your body, at least once every two months, for 4-8 days at a time. You might not want to, but you’ll feel so much better in the long run. You’ll also reduce the risk of injury.

Form is queen.

Because you have the timer going, it feels like you should always go as fast as possible. You should go at a clip, but always with good form. Do NOT flail your body around. You will injure yourself, if not now, then eventually. Injury sucks. And if you’re addicted to your HIIT and can’t exercise, you’ll be tempted to work out anyway, and injure yourself even worse. DON’T DO IT.

What is good form? You’ll have to constantly learn and tweak it, and it varies from exercise to exercise. Educate yourself. It can be fun, actually. Generally, it means keeping your body tight and controlled, in good alignment, with a straight back.

Yes, this matters for bodyweight exercises. A lot. I have injured myself with improper shoulder alignment on push-ups and improper knee alignment on side lunges. It matters even more when you’re dealing with weight. If you decide to pick up kettlebells, go light before going heavy and get the assistance of a trainer or watch some YouTube videos.

And often, programs that rely on HIIT don’t pay enough attention to form. So police yourself and be vigilant!

HIIT isn’t best for complete beginners.

If you’re very new to exercise, you should really be sure to go at a pace you feel comfortable at first. HIIT might push you to be sloppy with your form and then establish bad habits that would cause you to injure yourself.

I know that sucks, frankly, because all the amazing benefits above are a great incentive to start with a healthy habit. But here are some suggestions:

Do AMRAPs instead. It’s still a time-sensitive workout, but you don’t have the stress of rest periods and work periods.
Do circuits. Find a beginner’s circuit and take your time.
Convert an HIIT workout to an AMRAP or circuit. This will require you to assign a certain amount of reps to each exercise, which you can do beforehand or you can do after one round. See how many reps of an exercise get you to moderate fatigue, and stick with that for the rest of the workout.
If you still really want to do HIIT, increase the rest time. If you’re new, no matter how simple the exercise, 10 or 15 seconds isn’t enough to get prepared for the next exercise. You might want to start with a 1:1 ratio (30 seconds rest, 30 seconds work, for instance).

Weights and HIIT.

Adjust your exercises and weight accordingly.

I used to think weights shouldn’t be used in an HIIT format because of issues with form, and how the stress of the timer can push us to complete one more rep when we shouldn’t. After doing Hannah Eden’s FYR and following her for a while, I’ve changed my mind. However, be careful.

And be smart. Consider using a lighter weight that you would on a regular circuit so that you can go a little faster and complete the 45 or 60 seconds without running risk of injury. And if you’re doing a tabata, or an HIIT with relatively short work intervals, consider very simple movements with weights, or just bodyweight. If you’re doing a long combo exercise, like low knee up-downs and jump ups, you won’t get enough reps in before 20 seconds is up to really make it worthwhile.

Compound exercises are better for intensity training in general, and especially for longer intervals, but still keep them fairly succinct. For instance, I’m not a fan of bicep curls in an HIIT workout. It’s a fairly small muscle and gets exhausted fairly quickly, so if you’re doing a 50-second interval, you’ll likely get tired before it’s up. Or, if you lower the weight so you can keep going for 50 seconds, you’ll find that you’re not hitting a very high intensity. It might work fine for 20 seconds, however.

When weights don’t work with HIIT.

The biggest pitfall is doing an exercise that requires balance and patience foremost. I recently did crab reaches with a heavy (for me) kettlebell and almost lost control of a large piece of metal over my head. I got sloppy with my form because of the time constraint. Anything that requires you some stability for your safety really shouldn’t be included in HIIT. In fact, anything that feels remotely dangerous in any way should never be included in HIIT. Leave those exercises for circuits and give yourself time to get your bearings.

What DOES work with HIIT.

One thing Hannah Eden does, which I think is often a good idea, is she makes mini-AMRAPS during longer intervals of 60 or 90 seconds. This means that you might do 6 high pulls and then 6 burpees, alternating, for the interval. By breaking up a weight-bearing exercise with a bodyweight cardio one, you don’t run the risk of fatiguing our muscles to the point of dangerous failure.

So what weighted exercises work well? I love squats, lunges, thrusters, deadlift/high pull combos, overhead presses (these can be dangerous, so drop the weight down if your arms get wobby), swings. Complicated kettlebell moves like crab reaches, windmills, turkish get-ups, etc., should only be done without time constraints. Others, like snatches, can work but only if you feel secure in the movement.

In conclusion.

HIIT is fantastic for a fat burning boost, but in the long term, it should be folded into a workout program alongside other workout structures (find some ideas here).