A study has suggested that high-intensity interval training (HIIT) is only effective as a means of improving fitness when performed at 60-second intervals.

Research from Liverpool John Moores University points to a "sweet spot" which exercisers need to hit in order to make HIIT beneficial – with 60-second breaks being effective and 30-second and 120-second rests not.

Researchers at Liverpool John Moores University compared two popular HIIT protocols (60HIIT and 30HIIT) performed for six weeks, three times per week, in a sample of 26 previously sedentary men and women.

60HIIT means six to 10 60-second intervals with 60 seconds of rest, whereas 30HIIT means four to eight 30 seconds intervals with 120 seconds of rest.

They kept track of training adherence and intensity remotely via a heart rate monitor that fed info through a mobile app.

The researchers looked at three parameters of fitness: aerobic capacity, stiffness of arteries, and body composition (meaning how much muscle and fat they had) during the six weeks of HIIT.

Aerobic capacity increased after six weeks of 60HIIT but there was no difference for 30HIIT on any of the three parameters.

This means that 60HIIT should be used over 30HIIT because the former improves fitness whereas the latter doesn’t.

Hannah Church, one of the researchers involved said: "In order for people to get the most out of HIIT, which may be the answer to the difficulties of paying for and getting to the gym, we need to get the timing right.

"Our research showed just how important this is, because we found that 30 second intervals with 120 seconds of rest meant that participants’ heart rates didn’t stay up. 120 seconds is just too long to be resting for!"

The results of the research were presented at The Physiological Society early career conference, Future Physiology 2019: Translating Cellular Mechanisms into Lifelong Health Strategies.