A woman doing spring intervals on an assualt bike

SIT is the new HIIT: what is sprint interval training?

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Pushing your body to its limits is the latest workout trend – here’s how to sprint safely.

Sprint training shouldn’t just be something you find athletes doing on a running track. It’s actually a workout style that’s easily translatable to the gym – you may have even done it before when pushing yourself on a treadmill or spin bike in a high-intensity workout class.

As the name suggests, it involves intervals of work and rest. “SIT is a derivative of HIIT,” explains Melissa Weldon, head coach at workout studio Sweat It. “However, HIIT tends to work in hard intensities with eight of out 10 efforts, whereas SIT aims to work at maximal effort – you’ll be pushing yourself to a 10/10 difficulty.”

For that reason, the intervals in SIT tend to be shorter than in HIIT – it’s impossible to maintain your absolute max output for long. In a comparative review of the two training styles, published in the British Medical Journal, researchers defined HIIT as working at 80% of your maximum heart rate for around four minutes of work and three minutes of recovery. On the other hand, SIT was best done with 30 seconds of work with four minutes of recovery, or 8 seconds of work with 12 seconds of recovery.

“HIIT training is more suitable for most people who aren’t athletes or in a class environment as it’s slightly easier, where SIT requires better fitness and conditioning so you can maintain excellent form for your short, maximal efforts,” adds Weldon. 

Women wiping their faces on bikes after sprint training
SIT is done at extremely high intensities and all out effort

The benefits of sprint interval training

In a paper from June 2021 published in Medicine & Science in Sports & Exercise, sprint intervals performed on a bike improved both muscular and cardiovascular markers in the body. After eight weeks of training three times a week for 15 minutes, participants increased their muscle volume in their thighs, overall muscle mass, neuromuscular power and oxygen consumption. Most impressively, the participants were all aged 50-68, the age at which these markers of health tend to decline.

While there are other ways to increase your muscle mass, Weldon says “the beauty of SIT is in its efficiency. SIT training massively outperforms other styles of training in regards to increasing aerobic fitness and lean muscle mass in a shorter amount of time.” 

This small amount of time spent training is a huge bonus for many of us time-poor people. Who wouldn’t want to do just 45 minutes a week for a huge increase in fitness? According to a review of studies by RunRepeat, SIT actually requires 61% less overall time spent exercising than HIIT – and 71% less than medium-impact training.

Be cautious of too much SIT

The work time of SIT is so small for a reason – to avoid overdoing it. More is not always more when it comes to high-intensity training, and while there’s no one-size-fits-all answer to how often you should practice SIT, the generic advice is to avoid doing too much of it.

“SIT should be done two to three times per week max. I would suggest starting at twice per week and then gradually increase the effort time and frequency. This allows the body an opportunity to safely adapt to the intensity of the training,” says Weldon. 

A woman running on a treadmill with a trainer next to her timing her intervals
SIT is best done in a class where a trainer can help you push yourself

 “It is not a training style to be taken lightly, and I would suggest it is something to be approached with a baseline fitness level. Everyone can work at 100% effort but the risk of injury in an untrained person would be much higher.”

It’s important to remember that any form of exercise is a stress on the body, and a workout that’s as intense as SIT will be hugely demanding on the nervous system. That is what makes it so effective, but it also demands a huge amount of recovery to make sure that you aren’t constantly in fight or flight mode. 

How to do SIT

In order to know if you’re going at your max effort, you’ll either need a lot of experience with training and pushing your body or the ability to monitor your pace and heart rate. Given that you’ll be working in such short time frames, it’s probably not worth the distraction of checking your tracker to ensure you’re going at full pelt. The best way to do SIT, then, is probably in a class with a PT who can tell you when to ramp up the effort and count down the seconds.

The best SIT-style classes

Most of the workouts in these studios will include some element of SIT – encouraging max performance on the last few seconds of your treadmill section or upping the intensity on your bike. 

  • Guts & Glory at Sweat It

    Sold as ‘the hardest workout on the planet’, this doesn’t only push you to your max on the treadmill with elements of all-out effort, but also tests your endurance and strength on the rig. 

  • Barry's Bootcamp

    The original treadmill workout will push you for a full hour, with intervals of SIT spread throughout the class.

  • HIIT & Run at Victus Soul

    A mix of on the floor HIIT and treadmill sprints makes this the ultimate in high-intensity training. 

Images: Getty

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Chloe Gray

Chloe Gray is the senior writer for stylist.co.uk's fitness brand Strong Women. When she's not writing or lifting weights, she's most likely found practicing handstands, sipping a gin and tonic or eating peanut butter straight out of the jar (not all at the same time).