The Science Behind HIIT Training

fitness model

The Science Behind HIIT Training

HIIT stands for High Intensity Interval Training. As the name suggests, HIIT workouts involve short ‘maximum effort’ exercise intervals, lasting anywhere from 10 seconds up to 5 minutes, followed by rest periods of shorter, longer or equivalent duration. Generally, the shorter the interval, the higher the intensity, and vice versa.

We have all seen and heard about the infamous results of HIIT training, but we thought it was high time that we deep dived into the science behind it and WHY its so effective!


You may have participated in HIIT-style workouts before, without even realising! Group exercise classes such as Spin and Boxing, and everyone’s ‘favourite’ – the beep test! – follow HIIT principles.

And…you may have heard on the grapevine that HIIT has advantages over continuous, moderate intensity exercise (ie. running 5km at a steady pace), particularly when it comes to weight loss and cardiovascular fitness. You’ve heard correctly!

We’ve reviewed the latest literature to show you what scientists are saying about these key benefits of HIIT training.

1. HIIT burns at least the same amount of body fat, in less time compared with steady-state cardio.


A recent study demonstrated that healthy men burned up to 30% more calories with HIIT training, compared with steady state exercise. Another study involving young women aged 18-30 years old found that those who followed a 20 minute HIIT program lost more body fat (a 2.5kg reduction) than those who followed a 40 minute continuous, moderate intensity program using a spin bike.

Why does this happen? Scientists believe that HIIT training increases whole-body fatty acid oxidation (ie. fat burning!) both during and after exercise, compared with steady-state, moderate intensity exercise.

In fact, your metabolic rate may increase by a whopping 6-15% after completing your HIIT workout. So – you continue to burn through calories, for as long as 24 hours afterwards! This is because the recovery process following HIIT is energy-consuming in itself. Anaerobic energy production, which is required for high intensity exercise, depletes glycogen stores and creates a build-up of lactic acid and hydrogen ions in your muscle tissue. Converting lactic acid back into glycogen requires energy. Furthermore, high intensity exercise usually elevates your body temperature and heart rate more than steady-state cardio, and may be more stressful on muscles due to the explosive bursts of power needed to perform intervals. Repairing muscle tissue fibres and regulating heart rate and blood pressure also require energy.

2. HIIT improves your fitness and endurance.


A famous study conducted by Dr Izumi Tabata, one of the ‘brains’ behind HIIT training, showed that exercisers who performed a four-minute HIIT program on a spin bike five times a week improved their VO2 max (a measure of the how effectively your body uses oxygen during exercise) by 15 per cent after six weeks. In contrast, people who exercised for 60 minutes at a moderate intensity five times a week only improved their VO2 max by 10 per cent.

 Another study involving young, sedentary men found that 12 minutes of sprint interval training three times per week saw the same improvements in energy metabolism as men who were doing 40-60 minutes of cycling five times weekly.

3. HIIT improves your body’s ability to burn fat


Last but not least, a review of multiple studies using elite and recreational exercisers concluded that HIIT training improved exercise performance and cardiovascular fitness by 6-20% within only 2 weeks. 

Why does this happen? HIIT training improves your body’s efficiency at utilising fat as fuel during a workout. At a cellular level, HIIT increases the number and the functioning of energy-producing cells, called mitochondria, as well as the number of enzymes involved in energy production within muscle tissue. HIIT also increases the number of capillaries supplying fresh blood rich in oxygen and nutrients to working muscles, for energy production.

The good news doesn’t stop there. There is evidence to suggest HIIT training improves insulin sensitivity and glucose metabolism, reduces blood pressure and cholesterol, and preserves lean muscle mass more so than steady-state cardio.

So what are you waiting for? Arena Fitness can help you achieve your health and fitness goals faster!


Health update | In line with the Prime Minister’s announcement, it’s with sadness that we let you know that effective from midday Monday 23rd March 2020, we will be temporarily closed nationally. Learn More