It’s undoubtedly been one of the biggest fitness trends of the last few years and HIIT (high-intensity interval training) shows no signs of going away. Now, a group of researchers in Sweden have shed new light on why HIIT offers such an effective workout.

Scientists at Sweden’s Karolinska Institutet have been investigating the specific benefits behind the training and why a few minutes of HIIT is enough to produce an effect at least equivalent to that achieved with long doses of traditional endurance training. Their findings, which are published in the scientific journal PNAS, highlight a specific cellular mechanism linked to the activity and also provide clues as to why antioxidants undermine the effect of endurance training.

To investigate what happens in muscle cells during high-intensity exercise, the researchers asked male recreational exercisers to do 30 seconds of maximum exertion cycling followed by four minutes of rest, and to repeat the procedure six times. They then took muscle tissue samples from their thighs.

They found that HIIT has a significant impact on the calcium channels in muscle cells and this can in turn help to create more mitochondria. Mitochondria act as the cell's power plants, providing energy, so changes that stimulate the formation of new mitochondria help to increase muscle endurance.

"Our study shows that three minutes of high-intensity exercise breaks down calcium channels in the muscle cells," said Professor Håkan Westerblad, principal investigator at Karolinska Institutet's Department of Physiology and Pharmacology.

"This causes a lasting change in how the cells handle calcium, and is an excellent signal for adaptation, such as the formation of new mitochondria."

The findings build on previous research which has shown that HIIT can have a wide range of benefits. As well as helping pensioners to increase circulatory capacity and their ability to carry out daily tasks, HIIT has also been shown as an excellent way for young people to offset the effects of a high-fat meal.

Speaking to Health Club Management earlier this year, Les Mills CEO Phillip Mills said the health and fitness industry’s love of high intensity interval training (HIIT) is unlikely to abate any time soon, because the ethos make it the ideal fit for modern lifestyles.

“HIIT is going absolutely insane for us and it’s all people seem to want at the moment,” he said.

“If you want a great physique – you want to do HIIT.It’s great for our physiology to be carrying out a wide range of different movements. And participants are not just burning fat – they’re also getting a huge hit of hormones.”