From HIIT To LIIT: Why Exercise Is Slowing Down

I have this idea in the back of my brain that 'peak fitness' looks like being able to repeatedly jump onto a box before doing some burpees. It requires having the strength and stamina to jump and squat and kick and sprint in quick succession. It looks, essentially, like HIIT.

HIIT (high-intensity interval training), as you almost certainly know, is an intense cardio session that combines aerobic exercising, weightlifting and calisthenics at maximum capacity for short bursts of time, followed by short periods of recovery. While it seems intimidating, it’s sold on classes' relatively short run time – the idea being that if you can get through 20 seconds once, you can get through 20 seconds again. For that reason, it is often celebrated as the most 'efficient' and 'effective' way to work out, especially if you’re short on time.

There are physical benefits: interval training helps build cardiovascular fitness and can help develop a healthier heart and circulatory system, according to Howard Knuttgen, research associate in physical medicine and rehabilitation at Harvard-affiliated Spaulding Rehabilitation Hospital. But while it is improving your internal health, it could be damaging your body.

This is because high intensity also means high impact – and the repeated impact of short bursts of exercise can be harmful to your joints. A Rutgers study published in 2019 found that people who engage in high-intensity interval training are at greater risk of injury, especially in the knees and shoulders. Researchers looked at the number of injuries relative to exercises common in HIIT workouts, like push-ups, lunges and burpees, and found that contributing factors to increased risk of injury were poor form and muscle overuse. 

This is perhaps one reason why many people are making a deliberate shift towards working out in ways that don’t increase risk of injury. Another could be that doing HIIT at home during a pandemic doesn't always work – especially if you have limited space, echoey floors or live above some sensitively eared neighbours. Enter 'low impact' workouts.

While high impact aims to push you to your limits in a short period of time, low impact is focused on finding ways to improve your physical strength without straining your joints. Louisa Drake, creator of the Louisa Drake Method (LDM) and owner of the London-based LDM studio, tells me: "Trend forecasters LSN Global have predicted that 'conscious deceleration' will be big in the next decade of wellness. The popularity of LIIT (low-intensity interval training) has been growing and will continue to rise."

In her experience, low impact workouts and restorative fitness (exercise that focuses on easing pain and restoring joint function through simple movements) have been growing in popularity "among busy professionals, parents and stressed-out students alike". She says this is partly because people are becoming more aware of the longevity of their bodies and the importance of resting and looking after themselves. "We are attracted to restorative classes that reduce mental stress and anxiety, and offer physically calming effects by moving at a slower pace."

Third Space, the London-based luxury health club chain, echoed this. A spokesperson for the company said: "There has been an increased focus on recovery as part of working out [in our clubs]. There’s been a 47% increase in its mind and body programme, which has led to them adding 100 more yoga classes to the timetable across all clubs."

Workouts that centre around yoga or barre are just one form of low impact training. If you love the adrenaline rush of intense circuits, low impact does not have to mean low intensity – it just means focusing on cardio which is gentler than HIIT, where your joints are in constant fluid motion. There’s a world of different exercises that get your heart pumping without the same risk of jarring your knees or your spine, such as swimming, rowing and cycling.

Strength training can also be low impact, as long as you do it right. HIIT doesn’t give you the opportunity to correct your form, which over time could cause damage. Moving towards a low impact training method gives you the time and space to strengthen your body properly. Emily Taylor, cofounder and head of personal training at Grow Fitness, says: "No matter your age or athletic ability, focused strength training is the key to longevity, mobility, improved performance and lower injury risk." 

While HIIT is definitely not completely off the table, to get the most out of your workouts you should definitely aim to incorporate more low impact exercise. Not only will it decrease the risk of injury, it will help you attain the form and strength to better protect yourself from injury when you do something more high impact. And it doesn't require a fancy gym membership – you can get great results at home, too. (The lack of jumping will certainly keep your neighbours happy.)

If that image I described as 'peak fitness' at the beginning of this piece intimidates you in any way, rest assured that low impact is far more accessible, and that image is changing.