HIIT workouts explained – including why you should be doing them

HIIT is a divisive subject, and you’ll see a lot in the media extolling its virtues as well as articles declaring it to be a danger. The reality is much more nuanced than that, and it’s worth explaining the actual definition of HIIT as well as how the word is used within the fitness industry.  

True HIIT training is really only applicable to high-level athletes. It involves less intense training combined with very short bursts (10-20 seconds) of all-out max effort.  

A sprinter would benefit from this level of training, but the average exerciser doesn’t need to push their heart rate to the max to see results.  

Nowadays, the term HIIT has entered the mainstream, and while it still refers to interval-style training, the high intensity part simply means the exerciser pushing themselves into a higher heart rate zone for short bursts, rather than max effort. 

The high-intensity intervals can vary in length, but are always short: 10 to 30 seconds as a guide. Recovery intervals also vary; anywhere from 30 seconds to four minutes, depending on fitness levels and recovery times.   

This differs from steady-state cardio, which might take the form of a 10-minute run on a treadmill, or an hour-long bike ride along a flat path. In these instances, our heart rate stays pretty much the same throughout the activity.  

Speaking to Exceptional, Jack Claxton, an expert personal trainer (PT) for David Lloyd, said: “HIIT workouts offer a quick alternative to steady-state cardio. Typically in a HIIT class, you’ll burn more calories in a shorter amount of time. Expect a tough and varied session when attempting HIIT, as it involves short bursts of explosive energy with rapid recovery.” 

HIIT workouts can be incredibly good fun, and very rewarding. There’s something uniquely satisfying about pushing yourself beyond your perceived capabilities. HIIT offers a great opportunity to do that, without completely burning yourself out like you would if you tried a 20-minute sprint, for example.   

One of the biggest benefits of HIIT is it’s a style of exercise that can be tailored to anyone. You don’t need to tackle a HIIT class involving tuck jumps or multiple push-ups if that doesn’t appeal – instead, you can find a form of HIIT that works for you.

“It’s important to remember that it can be different depending on your ability level,” Claxton reminds us.   

“This type of training offers many benefits – it’s often fun, it goes quickly, and leaves you feeling great as it releases endorphins (the feel-good hormone) making you crave the feeling of success after completing one of these workouts.”   

Training in this way can have many advantages, and the benefits extend way beyond just making you fitter in a shorter amount of time – as we explore below.

Research evidence suggests that some of the exercises typically associated with HIIT workouts can contribute to cognitive health.

One study into cognitive decline in relation to lack of physical activity showed that weight-bearing exercises (such as such as squats, push-ups and burpees) can improve brain function.    

It’s one of the reasons that medical journalist Dr Michael Mosley of The Fast 800 is a fan of HIIT training. 

“I first came across HIIT in 2012,” he told Exceptional. “I was making a Horizon documentary, and I thought ‘this is some interesting stuff’. There’s a lot of research showing that HIIT is very beneficial.

“It’s good for the brain, for type 2 diabetes, and for cognitive conditions like dementia. Any resistance exercise is great – it works the biggest muscles in the body – but there’s also some research that the up and down motion of push-ups and squats helps with oxygen to the brain.” 

The motion of exercises such as squats, push-ups and burpees increases blood flow to the brain. This is particularly in evidence in HIIT training, as the blood flow is raised, then lowered again repeatedly. 

Blood flow to the brain is usually something that decreases with age, which is linked to diseases such as dementia, but the increased blood flow from HIIT helps deliver oxygen and nutrients. In turn, the connections between neurons in the brain are strengthened, thus lowering the risk of cognitive diseases or decline.  

There is also some interesting research on the effects of HIIT on memory, with studies showing that older adults who exercised in short, intense bursts saw up to 30 per cent increase in memory compared to those who only exercised moderately.  

As with any form of cardio exercise, the condition of heart and lungs is improved when we work them harder. 

Because HIIT involves an intense bout of exercise followed by recovery, then repeating that several times, aerobic capacity (getting more oxygen to your muscles) is greatly increased. 

This in turn can result in lower blood pressure, weight loss and improved cholesterol levels.  

HIIT can be particularly beneficial in terms of maintaining muscle, which is important for strength and mobility, and typically declines as we age.

Studies have shown that older adults engaging in regular HIIT improves the age-related decline in muscle mitochondria, the compartments in our cells that play a key role in maintaining muscle mass. 

Improving the function of our muscles also helps with endurance, not only in exercise but in everyday life – and it tends to be these ‘little wins’ that inspire us to keep going. For example, improving strength in your leg muscles will enable you to walk or run further for longer. You’ll also recover more easily after workouts or activities such as heavy gardening or DIY.

If you’re looking to lose weight, HIIT can be a great choice. There’s no  evidence that HIIT is any better for weight loss than any other form of exercise (a 2019 study claiming as much was retracted), but combined with overall lifestyle factors such as eating healthily, it can result in a reduction in body fat.  

The most appealing factor about adding HIIT to a weight loss regime is that it takes up relatively little time in comparison to steady-state cardio, leaving you more time to be active in other ways, such as taking a long walk with the dog, or doing a yoga class.  

HIIT can also help manage blood glucose levels, which can help anyone trying to manage type 2 diabetes, and effects can be felt in as little as two weeks.  

Although any form of exercise can play a large part in reducing or even reversing the effects of type 2 diabetes, short bouts of HIIT can be just as effective as longer periods of continuous exercise.  

It’s clear that HIIT has its advantages, but it may not be suitable for everyone.

The intensity of some forms of HIIT puts a large amount of stress on the body, especially our joints. This means that it’s not suitable for anyone suffering from osteoporosis, osteoarthritis, or any bone or joint disorder that could be made worse by high impact exercise.   

Knees can end up irreparably damaged from repeated high impact exercise, especially if your training involves a lot of jumping.

One way to try and combat this would be to opt for a lower impact form of training, such as doing sprint intervals on a spin bike, for example.    

Again, because of stress on the body, anyone with any pelvic health issues such as incontinence or prolapse should also steer clear.   

Because of the intense nature of it, anyone with a heart condition should consult with their doctor before attempting a HIIT session.

If you do want to give it a try and you have little experience, take the time to train properly. Find a qualified, knowledgeable instructor who will correct form and technique as needed and tailor any programme to your ability and needs.  

An element of HIIT training can be introduced whatever your exercise level. As with anything new, it’s a good idea to talk to your doctor or other healthcare professional if you have any existing health issues, or any concerns.  

If you’re a beginner to exercise, Dr Mosley suggests thinking of HIIT as simply upping your pace at certain times.  

“Focus on introducing an element of briskness to your activity,” he says. “You can do it when you’re walking. It only takes 20 or 30 seconds of pushing yourself, have a breather, do it again, do that a few more times. 

“If you’re swimming or jogging, put in a little sprint and try to keep it up for 20 seconds.” 

You can also find beginners HIIT workouts on YouTube. However, it maybe best to master some of the basic movement patterns, such as squats and lunges, and learning how to lift weights safely and effectively, before jumping in.   

Another good idea is to download a playlist to keep you motivated. Spotify Pumped will curate a dedicated HIIT playlist tailored to your ability, the duration of your workout, and your music tastes. An alternative is to create your own, with faster tracks thrown in (try 120bpm or higher) that you try and keep up with.  

If you’re a seasoned exerciser and ready to go, try a circuits class or dedicated HIIT class at your local gym for a real cardio blast.

Outdoor bootcamps often use HIIT training techniques too, and take place in all weathers – leading to some fun as you try to flip tyres in the pouring rain.   

Current government guidelines recommend that adults aim to do 75 minutes of vigorous exercise a week (although only if you are already physically active for those aged 65 and above).

As outlined, HIIT sessions don’t need to be long in order for you to see the effects. With this in mind, 30 minutes two or three times a week is sufficient. This will give plenty of time for recovery and variation; the rest of your week can be spent exploring other ways to keep fit, reducing the possibility of injury or demotivation.  

Allowing plenty of time for recovery between sessions is key. Doing a lot of HIIT training increases levels of cortisol, the stress hormone, which makes this style of training harder to recover from.  

The increase in cortisol can also be particularly pertinent for women who might be struggling to lose weight after the menopause, since cortisol tends to increase around this time anyway. Cortisol can slow weight loss since it tries to make our body hold onto fat. 

Our bodies use glycogen to fuel exercise, a type of carbohydrate stored in the muscles. We then replenish these glycogen stores when at rest, but if we don’t recover sufficiently, we end up weaker and more fatigued.  

Slower recovery can lead to a higher risk of injury, especially as we age, when recovery between training sessions is paramount.  

All this intensity with too little recovery can lead to demotivation. Whilst you may start your fitness journey full of enthusiasm and motivation, burnout, tiredness and injury might mean you come to dread your workouts, and you want exercise to be something you enjoy.  

With all of that said, if you’re reading this thinking HIIT sounds like the worst possible form of torture, then just don’t do it – it’s important to find ways to workout that you enjoy.  

However, if you do decide to give HIIT a try, make sure you start with a workout tailored to your level of fitness, and gradually build the time and level of intensity. Above all, have fun.