What the heck is a HIIT workout anyway?

Published: 22 May 2020.

HIIT has been big for many years now with the likes of personal trainer Joe Wickes; Olympic heptathlete Jessica Ennis-Hill and Hollywood superstar Chris Hemsworth all using the training method to get in shape. But why is HIIT so effective for so many people and how can you make it work for you? We look at the science to find out…

What is HIIT?

HIIT stands for High Intensity Interval Training. It generally combines quick bursts of hard exercise (20-30 seconds of all-out 100% effort) with periods of complete rest or lower-intensity exercise. This is then repeated for a number of sets so that your heart rate is forced to spike up and back down again.

Why do people rave about the benefits of HIIT?

The reason people are so passionate about HIIT is that you get great results in relatively short sessions of just 20-30 minutes. Even better, you don’t need tons of equipment or space for a HIIT session. This means you can do a HIIT circuit at home or in your garden and get great results.

What sort of exercises are featured in a session?

Usually a HIIT circuit will consist of bodyweight exercises, such as press ups, burpees, squat thrusts and so on. Anything that gets your heart rate up fast without requiring tons of equipment.

Why are HIIT workouts so effective?

When done properly, a HIIT workout burns maximum fat and builds maximum muscle because of the contrast between high intensity, all-out effort and rest.

The reason for this is that when you work as hard as you possibly can, your body starts to work anaerobically. This means that you’re deprived of free oxygen, lactic acid is produced in your muscles, adrenaline kicks in and you start to burn fat and build muscle.

When you do this repeatedly through sessions of all-out effort – for 20-30 seconds, say – followed by 10 seconds rest and then all-out effort again, you’re effectively forcing your body to work anaerobically over and over. This leads to the fat-burning benefits we just mentioned.

Even better, hours after your HIIT session is done, your body can still be burning fat because your metabolism has been kick-started. That basically means you get a double whammy of benefit – both during and after your session is complete.

How many calories does a session burn?

When it comes to calculating calorie burn, it’s important to caveat that everybody is different. Factors such as your gender, weight, age and fitness level all come in to play when calculating it. However, according to a 2015 study in the Journal of Strength and Conditioning Research, when compared to ‘steady state’ activities such as running and cycling, HIIT-based workouts came out on top for per minute calorie burn. They found HIIT burnt 12.50 calories per minute versus 9.48 calories per minute for running and 9.23 for cycling.