Scientists have figured out why interval training is so effective.

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High intensity interval training (HIIT) is all the rage in the fitness industry – and now research has determined why it’s just as effective as longer but less demanding workouts.

These days most gyms offer some form of HIIT training, where clients are pushed to exercise at their peak heart rates for brief periods (anything from seconds to a few minutes) and then cool down for a few minutes, before picking the intensity back up again.

It almost seems too good to be true. You’re exercising for shorter periods of time, but reaping bulk health benefits like improved insulin sensitivity and the same endurance and muscular fitness longer workouts provide.

Looking for a true core workout? Paper Tiger show us one in the video below. (Post continues after video.)

A recent study by scientists from the Karolinska Institute in Stockholm, published in the journal PNAS, has detailed how and why HIIT training can deliver so many benefits.

Relatively active men were required to complete one fitness session which involved 30 seconds of high-intensity cycling repeated just six times. The participants rested for three minutes in between each set.

“What we found was a breakdown of these channels that was totally unexpected,” Hakan Westerblad, a professor of physiology and pharmacology from the Karolinska Institute, told TIME.

“We have never seen anything similar. We saw a large production of free radicals, and these free radicals were specifically hitting the calcium channels. Normal training also increases the amount of free radicals, but not by as much as interval training," he said.

Furthermore, the extreme pressure of HIIT workouts caused the cells to go into a emergency mode.

"During any physical training, the cell senses, 'I have a problem here'," Westerblad explained. (Post continues after gallery.)

"So to be better safe than sorry, they adapt so the next time they experience the intense exercise, the problem is lessened."

However there is one particular group this form of training is ineffective for. Elite athletes who are accustomed to HIIT workouts see less benefit over time, as their bodies have adapted to the short bursts of activity.

So if you’re not a fan of long workouts, HIIT training might be the perfect option for you. However, it is recommended for those with a better than average level of fitness so talk to a PT or your doctor before jumping into it.

Have you tried HIIT training before?