For some people, exercise is all about how long they can push themselves – but for other people, the question isn’t “how long” but “how hard”? It’s all about stretching the limits of their own endurance, even if it’s just for a few seconds at a time.
That’s high-intensity interval training, or HIIT for short. HIIT is all about power and intensity over short periods of time. It’s a sliding scale (there’s no magical point where the workout suddenly changes from “aerobics” to “HIIT”), but in general anything with work periods under about 1 minute is considered HIIT. Much longer than 1 minute, and you just can’t sustain the “high intensity” part of the name.
Within the general category of HIIT you’ll find all kinds of different programs. Just to name two popular examples:
- Tabata sprints: invented by a Japanese professor named Izumi Tabata, tabata sprints call for 20 seconds of all-out effort, and then 10 seconds of rest, repeated for 4-8 minutes.
- Minute sprints: work as hard as you can for 60 seconds; then walk (or collapse) for 3-4 minutes; then work for 60 seconds again. Stop when you can no longer peel yourself off the ground for your work interval.
Running is the traditional exercise to do during the work intervals, but you can use any exercise that engages your whole body – bodyweight squats, burpees, jumping rope, or cycling are all fine. The only thing to avoid is an exercise that will hurt you badly if you fail a rep. No tabata clean and jerks!
Completing one of these programs (or any similar HIIT program; there are several and no one is “best” for everyone) should leave you completely gassed. If you aren’t sweating buckets and shaking at the end, you weren’t pushing hard enough. Many people even get dizzy, woozy, and nauseous – not because they’re sick, but just because they were trying that hard.
Why would you ever put yourself through that? Maybe because you love the intensity of a challenge – or maybe because you think that HIIT will help you reach your fat loss or athletic goals better than traditional “cardio.”
Is HIIT Better than Cardio?
HIIT is generally touted as a better alternative to jogging or other forms of “cardio.” But in fact, it’s more complicated than that. The choice of “HIIT or cardio” is a false dichotomy. You can do both, or you can do neither.
The big advantage of HIIT is that it compresses your workout into a much shorter space of time; it’s basically a way to squeeze more effort (meaning more benefit) into every minute. For example, this study found that, over the course of the entire day, very short bouts of HIIT resulted in basically the same calorie burn as typical “cardio” training, only with a much shorter time in the gym. And this study found that HIIT helped improve endurance capacity in recreational athletes, even though HIIT itself is not an endurance exercise. There’s also some evidence that HIIT is better for losing more fat, while keeping your hard-earned muscle.
On the other hand, HIIT is a tool to be used sparingly. You cannot simply replace every jog with a set of tabata sprints! For one thing, you’ll burn out in short order: exercising at that intensity every day is a terrible idea. So if you want to add volume to your routine, HIIT is not the answer, and there’s still a place for slower-paced cardio work alongside your interval training. For another, the research into all of these benefits is still pretty conflicting – for example, some studies find that HIIT improves insulin sensitivity, while others don’t.
This article takes a helpful comprehensive approach, noting that HIIT alone does not an effective training program make. The trick is to work HIIT into your training routine in an intelligent way, not to go all-out and fall into the “more is better” trap. So it’s not necessarily a question of “HIIT or cardio,” but “how can I combine HIIT and cardio to get the results I want?”
The answer to that will depend on your goals. Used effectively and fueled appropriately (more on this below), HIIT can be useful to almost anyone. But if it’s abused, it can also drive you straight into the ground.
What are the Dangers of HIIT?
HIIT is a powerful tool, but the power to help is also the power to harm. Abuse it, and that power will come back to bite you.
When you fight through a HIIT workout (assuming you’re really pushing it), you’re forcing your body through an extreme stimulus. There’s a reason why it hurts so bad: your body is warning you that you’re really pushing it. You can ignore that and keep going, but the fact remains that HIIT done right is a massive physical challenge, and very taxing to recover from.
Of course, that’s the whole point: to force your body to adapt to the challenge, so it bounces back stronger. But you don’t get stronger by doing the exercise. You get stronger by recovering from it.
Skimp on that recovery time, and you’re just beating yourself up again and again, with no chance to see the gain from all your pain. Eventually, you’ll simply overwhelm your body’s ability to keep going, and start noticing your performance go down the tubes.
Don’t let this be you! If you’re going to try HIIT, here are some tips for keeping it safe:
- More is not better. You should aim for the hardest workout that you can recover from adequately, not the hardest workout you can force yourself through with enough caffeine pills. Start with once a week (either replacing one cardio session or added in on a day when you aren’t doing anything else), and then maybe – maybe – build up from there. HIIT is one part of an effective workout plan; it’s not the only thing you should be doing.
- Carbohydrates are not optional. HIIT burns through the glycogen in your muscles like nothing else; if you don’t refuel you will eventually lose your capacity to put out that kind of effort in the first place. And just to be clear: “carbohydrates” does not mean a side of carrot sticks with your salad. It means starchy tubers: potatoes, sweet potatoes, or something similar.
- Pay attention to injuries. Pounding out the burpees or squat jumps is hard on your knees. Running at that intensity is hard on your everything. When the workout is over so fast, it’s easy to get caught up in the adrenaline and not realize how bad it hurts, so do a thorough warm-up before you jump in and err on the side of caution.
All the warning about the potential dangers does sound a little doom-and-gloom, but that’s not intended to scare you off the whole concept of HIIT; it’s just to make sure you go in with your eyes open. HIIT is a great way to work out if you like your workouts short and sweet. Many people see a lot of success with HIIT for weight loss, especially to pare down those last few pounds. It’s a perfectly fine way to improve your metabolic conditioning and overall fitness, when it’s used in a sane and reasonable exercise program.
On the other hand, HIIT can easily go bad, the same way that you can hurt yourself more with a jackhammer than with a chisel. More does not mean better – and if you’re going to do tabatas, make sure you’re eating appropriately!
Ultimately, it’s all about finding a workout plan that makes you feel good. HIIT can be part of that, but it doesn’t have to be.