HIIT: Your introduction to high-intensity interval training

Can you build muscle with HIIT? How long should it take? And will it really help you burn fat all day? Here’s your five-minute primer

To hear some trainers wax lyrical about high-intensity interval training (HIIT), you’d be forgiven for wondering why anyone ever does anything else. It builds lung power! It burns fat! It only takes ten minutes! It makes you more handsome! Okay, maybe not that last one... 

But while reports of HIIT’s effectiveness really aren’t exaggerated, you need to make sure you’re doing it right to get the best possible results. Done correctly, it can replace tedious cardio sessions as a means of more efficient fat loss. Done wrong, it’s a waste of time and effort – and might lead to injury. 

Here’s everything you need to know to start high-intensity interval training – alongside a handful of recommended workouts.

What is HIIT? 

HIIT stands for high-intensity interval training, which is pretty self-explanatory: workouts are made up of short bursts of intense exercise interspersed with easier recovery periods. ‘Intensity’ really is the key word here: you should be going flat-out during each interval, and really earning those rests. 

What are the key benefits of HIIT?

It can mimic the effects of longer workouts – or even outdo them – without the same time commitment. Part of this is because of the so-called ‘afterburn’ effect – research suggests that HIIT increases excess post-exercise oxygen consumption (EPOC for short), giving your metabolism a boost for hours after you’re finished. There’s also research to suggest that it can reduce resting heart rate and blood pressure in overweight or obese trainees. 

How can I start doing HIIT? 

First, decide on a work-rest ratio. Minimal rest is best for fat loss, but you’ll compromise on intensity – while more rest allows you to work on your power output. After doing 6-second sprints, for example, researchers at Loughborough University concluded that a 30-second rest was best for keeping the power up, which works out to be a 1:5 work/rest ratio. 

Other studies suggest that using a variety of work/rest ratios keeps your body from adapting to any particular one, and keeps fat loss rolling. Don’t worry too much about ratios at first, just go full throttle for as long as you can and then rest for as long as you need to catch your breath. Rinse and repeat.

What exercises are best for HIIT?

If you’ve got access to a gym, battle ropes are best – in a New Jersey College study, they produced more energy expenditure than every other exercise tested, and produced the highest average heart rate. 

No oversized ropes to hand? Your best option is probably burpees – the same study found this gruelling bodyweight exercise beat every other bodyweight move for V02 response. In case you're wondering, the session they used was 30 seconds all-out, then four minutes of rest, done 4-6 times.

What do I do during HIIT rest periods? 

You’ve got a few options. If you’re riding a spin bike or thrashing the rower, it actually makes sense to keep working, though at a much reduced pace: you’ll keep blood flow going, helping you to recover. 

If you’re doing bodyweight moves, it still makes sense to keep moving during your rest intervals: if you’re resting for more than a minute, you could even do some mobility work for the muscles you aren’t using in the high-intensity intervals. This is called active rest.

What HIIT workout should I start with?

Make your own. First, pick a move that’s not too technical and uses several muscle groups: cycling is ideal because you just mash the pedals, but burpees, battle ropes and jump squats all work well.

Then, pick how much ‘work’ you’re going to do: on a bike you can go harder, so less is fine, but for burpees you could go as high as two minutes.

Next, pick the intensity you’re planning to work at: if you’re relatively new to training this should be around 70% of your maximum effort, but veterans can go higher. It’s hard to accurately measure how hard you’re going, but one one way of telling if you’re at 70% is if you can still manage to get a short sentence out, but holding a conversation would be impossible!

Finally, pick a rest interval: this should be at least as long as you’re working for, but for fat loss it could be up to three times as long. As a rule of thumb, waiting until you’ve fully caught your breath should be long enough.

What’s an ‘easy’ HIIT workout that’s still effective?

A study published in the Journal of Strength and Conditioning Research found that test subjects doing a ‘descending’ sprint protocol – which they rated easier than an ‘ascending’ protocol that used the same distances – experienced a higher uptick in growth hormone and testosterone.

Try it yourself: sprint for 400m at 80% of your maximum effort (almost flat-out, but with a tiny bit of effort left in the old reserve tank), rest for as long as the sprint took, then repeat for 300m, 200m and 100m. It’s a lot easier than starting at 100m and pushing yourself to go harder every time.

How often should I do HIIT?

HIIT is supposed to be short, intense and challenging: if you can get mentally geared up to do it every day, you probably aren’t going hard enough during your efforts. Plan to go hard twice a week, then top up with other sessions focusing on resistance exercise to burn fat and build muscle. 

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