What is HIIT? High intensity interval training explained
HIIT stands for high intensity interval training. You swap short blocks of hard work with short breaks, and you repeat that a few times. For example, 20 seconds of squats, 10 seconds of rest, and again. The session is short, but during those work blocks you really go for it.
Sounds simple, and it is. Still, people often get it wrong: too long, too often, or only about getting sweaty. Let me explain what HIIT actually is, what it does, how often to do it and how it compares to CrossFit.
Updated: 2026-11-05
What HIIT means
The name says it all. High intensity means hard effort. Interval means you switch between work and rest. Before you start, you decide how long you work, how long you rest and how many times you repeat it.
Those three dials decide what you train. Short, explosive bursts with lots of rest train your speed. Medium blocks, the kind where your legs start to burn, train your ability to keep going. Longer blocks with equal rest train your endurance.
| What you mainly train | Work block | Rest | Rounds |
|---|---|---|---|
| Short and explosive | 10 to 30 seconds | 3 times as long as the work | 25 to 30 |
| Holding on when it burns | 30 seconds to 2 minutes | 2 times as long as the work | 10 to 20 |
| Endurance | 2 to 5 minutes | Same as the work | No fixed guideline |
These ratios come from the core text of the CrossFit method. See them as a starting point, not a rule.
By the way, an interval doesn't need a clock. Sprint from one lamppost to the next, then jog easy to the one after. That's interval training too.
What intensity really is
Lots of people think: the more I sweat and gasp, the more intense it was. That's not quite right. In CrossFit, intensity simply means how much work you do in how much time. Ten squats in twenty seconds is more intense than ten squats in a minute. A red face doesn't tell you much.
Intensity is also personal. What's hard for you might be easy for someone else, and the other way round. That's why every workout can be scaled: less weight, an easier version or a shorter distance. You go hard at your level.
Longer isn't more intense. The longer a workout lasts, the more you naturally start pacing yourself. That's why most CrossFit conditioning workouts last less than fifteen minutes. A 45-minute class without a break feels tough, but it's usually less intense than you'd think.
What HIIT does for your fitness (and what it doesn't)
HIIT trains your heart and lungs. According to the CrossFit method, intervals are the way to build your conditioning without giving up much strength, speed or power. That's why most of your conditioning work is best done as intervals.
The practical upside: it doesn't take much time. Short and hard, with rest in between, fits into a busy week. You don't need to run for an hour to work on your fitness.
And fat burning? You'll often read that HIIT melts belly fat, or that you keep burning extra for hours afterwards. I'm not going there. I won't promise you anything. Training makes you fitter and stronger. What happens to your weight depends on a lot more, like what you eat, how you sleep and how often you actually train.
An example: what a HIIT workout looks like
The best-known version is Tabata: 20 seconds all-out, 10 seconds rest, six to eight times. That's four minutes or less. Real Tabata means truly giving everything, and that's harder than it sounds. So not every 20/10 timer is Tabata.
Want to start at home? Here's how I'd do it:
- Warm up easy for five minutes. Walk, cycle or skip, and do a few slow squats.
- Pick two exercises, for example squats and push-ups against the kitchen counter.
- Do 20 seconds of squats and rest 40 seconds. Then 20 seconds of push-ups and 40 seconds rest again.
- Repeat that six times. That's twelve work blocks done.
- Walk it off and you're finished.
Going well? Then make it a bit harder, one step at a time: shorter rest, a tougher version or a couple of extra rounds. Other good home exercises are lunges, mountain climbers and burpees. Or head outside for the lamppost sprint.
Who HIIT is for
Almost everyone, as long as you do it at your own level. You don't need to be an athlete. For one person hard means a sprint, for another it's walking briskly up the stairs. Both count.
Starting from zero? Build a bit of a base first. And learn a movement properly before you do it fast. A squat that looks good can get quicker later. In CrossFit for beginners you'll read how that works in your first classes.
Got pain or an injury, are you pregnant or on medication? If you're unsure, check with your doctor or physio first. A good coach adjusts the exercises to that, but doesn't take over the role of your doctor or physio.
How often to do HIIT each week
My advice: start with twice a week, and don't go all-out every time. Pushing to the limit four to six times a week doesn't work for most people. You burn out, you're more likely to get injured and you actually get less fit.
What does work: training a few times a week at your intensity, and keeping it up. Mix it up too. Do short, hard blocks, but also strength, technique and now and then something longer. In CrossFit we say routine is the enemy.
A steady rhythm beats the occasional extreme workout. Next week easily turns into next month, right? Two sessions you actually do are worth more than five you only plan.
HIIT vs CrossFit and Tabata
Tabata is one type of HIIT, with a fixed setup of 20 seconds work and 10 seconds rest. CrossFit uses intervals and short, hard workouts too. But CrossFit isn't the same as HIIT.
| Topic | Many HIIT classes | CrossFit |
|---|---|---|
| Exercises | Often fixed circuits with light moves, like glute bridges and leg raises | Basic movements like squats, deadlifts, sprinting and rowing |
| The hard part | Often lasts long, so you start pacing | Usually under fifteen minutes |
| Setup | Almost always on a fixed timer | Sometimes on time, sometimes a set amount of work you finish as fast as you can |
| Strength | Little heavy work | Heavy strength training is part of it |
| Progress | Usually not tracked | You log your scores and repeat set test workouts to see if you're improving |
In CrossFit, being fit means you're good at lots of different things: short and long, heavy and light. HIIT is one piece of that. Want the full picture? Read what CrossFit is.
Like the mix of strength and endurance? Then have a look at the Hybrid Endurance classes on our schedule.
HIIT at home or in the box
Home works fine. You need very little and you're done quickly. The tricky bits are technique and sticking with it. Nobody checks if your squat looks right, and nobody notices when you skip one.
In the box (that's what we call a CrossFit gym) the workout is ready and a coach watches you. You don't have to figure anything out. You just show up. Want to try it first? Come and do two weeks of unlimited training. We're on the Cruquiusweg in Amsterdam East, with classes from early morning to the evening.
Want to get fitter with short, smart workouts? Build a solid base first.
With Your Strong Start you learn the movements properly with a coach, so you can safely go hard afterwards. You don't have to write a plan or work out how heavy to go. You just show up, we sort out the rest.
- 12 coached CrossFit sessions in 4 weeks, around 3 a week
- A personal starting assessment plus scalable Fit Test as your baseline
- A midway check, so one busy week doesn't break your rhythm
- Final assessment and repeat Fit Test: you see what changed
4.9 out of 5 on Google · 153 reviews
Short excerpts from public Google reviews.
€99 one-off · 12 sessions · personal guidance · no membership
No experience needed. No programmes to figure out. No subscription quietly running on.
Frequently asked questions
How long does a HIIT workout take?
The hard part doesn't need to be long. Fifteen minutes or less is often enough. Add a warm-up and an easy cool-down and you're done in about half an hour.
Do you need equipment for HIIT?
No. Your own bodyweight gets you a long way: squats, lunges, push-ups and burpees. Outside, you can sprint. A kettlebell, rower or bike is nice, but you don't need one to start.
Can HIIT target belly fat?
I won't promise you anything there. HIIT makes you fitter. What happens to your belly depends on much more than one type of training, like food, sleep and how often you actually train.
Can you combine HIIT with strength training?
Yes, they go well together. Intervals train your conditioning without costing you much strength. Just don't put all your hardest sessions back to back, so you get time to recover in between.