Michael Mosley, the man behind the 5:2 diet, explains his seemingly too - good - to - be - true new exercise method to Theo Merz.

What if instead of spending an hour in the gym every other day, you could get better results from two bursts of 20 seconds at maximum effort, three times a week?
It seems an outlandish claim but that’s the idea behind the new bookFast Exerciseby Dr Michael Mosley and the health writer Peta Bee. And given that Mosley is the man behind the Fast Diet, better known as the5:2, his latest pronouncement on exercise has been commanding attention.
“This is really nothing new at all, ” says Mosley, who trained as a doctor before moving into journalism and now regularly fronts science and health programmes for the BBC. “Fast exercise is just what we used to do as hunter - gatherers – doing short bursts of intense exercise, having a rest, but also incorporating it into your general life. ”
He adds thatHigh Intensity Training(HIT), which he champions in the book, has been used in its modern form for decades by athletes and fitness fanatics, but has yet to be fully assimilated into ordinary people’s exercise routines.
The advantage of HIT over extended, steady exercise is three - fold, Mosley says. “When you do HIT, you massively increase the number ofmitochondria[so - called " cellular power plants " which convert fat and sugar in the blood into energy] and their efficiency. Without the intensity, that doesn’t really happen. “Also, when you exercise intensively you release things called catecholamines – adrenalin - that is a fat - burning hormone. Levels of catecholamines can go up 10 - fold even after a 20 second burst. “Then, if you’ve done an hour’s standard exercise your appetite’s going to increase, so you’re more likely to have a coffee and a muffin and cancel out whatever calories you’ve just burned. There’s a compensatory lack of movement if you feel you ' ve done your exercise at the gym – people will just sit around on their arses for the rest of the day. ” But while these two lots of 20 seconds is an attractive proposition, it doesn’t tell the whole story of the routine advocated in Fast Exercise. The authors break the regime down into Fast Fitness and Fast Strength: the former can be maintained by riding a bike or running at full pelt for these two bursts, while the latter involves five minutes of basic exercises two or three times a week. They also offer obvious suggestions of ways to introduce more movement into your daily routine: from standing up and walking round while taking calls to running up escalators rather than standing on them. Put that way, Fast Exercise seems rather easier to get on board with; more like common sense than the “health revolution” it has been called elsewhere. Mosley acknowledges people may still be sceptical of what the book promises, but points towards the 45 studies cited which, he says, back up his claims. Can it ever be as popular as the 5:2, which suggests people eat normally for five days a week and then significantly reduce their calorie intake for two?(The Fast Diet was the most popular regime of 2013 butwas not without its critics.) Mosley hopes so: “There is a link between Fast Exercise and the Fast Diet, which is the idea that stress is good for you and that what doesn’t kill you makes you stronger. The intensity of fasting or exercise is absolutely crucial. “I hope this will change how people exercise. It has a broad audience and people should be able to incorporate it into their everyday life. ”How Doctor Mosley gets his Fast Exercise:Fast Fitness – two or three 20 - second bursts of uphill cycling at full pelt, twice a week Fast Strength – a varying routine three mornings a week, at home. For example: - 30 press - ups - 20 squats - 20 tricep dips on a chair - 20 lunges - 15 pull - ups on a door bar