Why it’s time to give fast HIIT workouts a miss and embrace your inner tortoise

FOR years, our exercise mantra has been “go hard or go home”, with intense spin classes and HIIT workouts promising we could get fitter in just 20 minutes or less.

But now things are slowing up on the gym floor, with an increasing number of experts recommending we take it down a gear.

Is your workout stressing you out?

HIIT – AKA high-intensity interval training – mixes bursts of hard, fast moves that aim to take your heart rate up to 90% of its maximum, with short recovery periods in which you rest.

“By working out this way, you get a huge spike in the level of the stress hormone cortisol, which helps the body to adapt and grow,” says Bryce Hastings, head of research for gym Les Mills.

During a rest period, your cortisol level should fall, but the gym’s research scientists found that didn’t happen for those who do HIIT. “We found their recovery was compromised and it was causing problems such as injuries, mood swings, fatigue and disrupted sleep,” explains Bryce.

Now the Les Mills team advise that people only do two 20-minute HIIT sessions a week, with at least two days’ rest in between.

And they aren’t the only ones suggesting a limit. Research by universities in Brazil found that two days of back-to-back HIIT exercise compromised the immune system, leading them to recommend at least one rest day between workouts.

It takes almost that long for our bright-red faces to return to normal, anyway.

Steady as she goes

LISS – low-intensity steady state, to give it its full name – cardio sees you swapping the short, sharp bursts of HIIT for longer steady runs or cycles where your heart rate reaches 60-80% of its maximum.

“There are years of research showing that this works – we just seem to have forgotten it in our excitement over HIIT,” says Niko Algieri, co-founder of London gym Equilibrium Total Balance.

“A couple of sessions of 45-60 minutes steady cardio a week will burn fat and work your heart and lungs to raise fitness.”

Sadly, strolling around the shops won’t quite cut it. Aim for a pace where you’re breathing hard enough to just about keep up a conversation while you move.

You get similar slimming success doing moderate exercise as well as with HIIT

If you’re super-fit, MISS – moderate-intensity steady state – might be more your style. “A common mistake when people don’t find LISS challenging is to extend the time for which they work out, but that can lead to injury,” says Bryce.

Instead, he suggests you step up the pace to “where you can say a sentence, but not have a proper chat.” So, for example, MISS would be a medium setting on the rower or a fast jog.

Remember, this isn’t going all out. “During HIIT you should barely be able to say your name,” says Bryce. “That’s not what you’re aiming for here.”

How low can you go?

Weight training the HIIT way gets you cranking out maximum reps in the shortest possible time (search for thousands of humblebrags). But it turns out this method might not be the most effective for building strength.

“The problem is it doesn’t allow you to focus on form at all – rarely do I see anyone doing a HIIT strength workout extending their muscles to their full range of motion,” explains Niko.

“That means you’re not recruiting all the muscle fibres and won’t be getting the optimum challenge your muscles need.”

Instead, try the weight version of slow exercise, LIRT – that’s low-intensity resistance training.

Aim for three sets of 10-15 reps per move, using a weight that’s heavy enough to make your last two or three reps feel hard. Make sure you push the weight out steadily and control it coming back. Then rest for 60-90 seconds between sets to let your muscles recover – a perfect window for a quick swipe right.

Before trying LIRT, it could be worth booking a session with a personal trainer. “Good form is key to getting results from slow training – and we have had to correct a lot of people who’ve fallen into bad habits doing HIIT,” says Niko.

Bend it like…

If your favourite part of any exercise class is the bit where you lie down on a mat and stretch, you’re in for a treat.

Slow and purposeful stretching is on the timetable at cool gyms such as Frame and Barrecore, and the LA trend for specialist “stretch studios” is set to hit the UK soon. But it’s more involved than just a bit of lying down.

Next-gen slow stretch classes focus deep into muscles to work a layer of connective tissue called fascia, and also push your muscles slightly further than normal, which helps to improve flexibility.

“The normal type of stretching you do after a workout releases tension created during exercise and brings levels of adrenalin and cortisol back to normal,” says Jayne Robinson from Frame. “Stretching classes do more than this, restoring a range of motion you may have lost.”

These stretches are best done in a class as there are rules to follow. “Work into the stretch gradually and avoid jerking or sharp movements. It’s OK to feel some discomfort, but if the pain becomes sharp, or your breath shortens, you’re going too far. The motto is ‘bend, not break’,” explains Jayne.

Slow down to slim down

So is this it for HIIT? Well, you don’t have to wave goodbye to that hot CrossFit trainer if you don’t want to – just balance out fast workouts with plenty of slow.

“Think of your body like a car, but with a few different petrol tanks,” says Niko. “You need to keep each tank full with a different type of workout to perform well. Do some exercises that challenge you, but add in some slower ones to restore.”

More and more research shows you get results working out slower, but smarter. One 2016 study by the University of Bath found similar levels of slimming success in a group doing HIIT five times a week as a group doing fire training sessions at a moderate pace.

On top of this, if you’re a new or less enthusiastic exerciser, a 2017 study from Iowa State University found it’s likely you’ll also enjoy your slower session more than an exhausting HIIT one.

And all trainers agree the best exercise for your body is the one you keep doing. Ready, set, slow!