Who, what, why: Is surviving on 20-minute naps bad for you?

The Solar Impulse is about to set off from China to Hawaii, as its quest to become the first solar-powered plane to fly around the world continues. But its pilot only gets 20 minutes' sleep at a time. Can this be healthy, asks Justin Parkinson.

For five days and nights the pilot will fly alone over the Pacific, taking 20-minute "cat naps", 10 to 12 times a day, and leaving the autopilot temporarily unobserved. He's been trained in self-hypnosis, allowing "the body to regenerate into a very deep relaxation and keep the brain alert enough" to monitor instruments when awake, it's claimed.

But Kevin Morgan, professor of psychology at the Loughborough Sleep Centre, warns that at least half an hour is needed for a restorative nap, and 90 minutes for a full sleep cycle.

The British Ocean Reunion team, planning to row across the Atlantic later this year, will operate an alternating system, where one person sleeps for two hours while another takes a turn at the oar. This would probably be a "better" length of rest for the Solar Impulse's pilot to emulate, Morgan adds.

He likens the pilot's situation to that of a junior doctor in Britain during the 1980s, having their own bedroom on the hospital premises but being continuously on call to deal with patients' needs for 48 hours. "They were left feeling utterly wretched," he says. "Adding up the amount of sleep they got, it might be quite respectable, say five or six hours. The problem was that it was grabbed in amounts of 10 or 20 minutes."

In sailing solo around the world in 2000, Ellen MacArthur got around five-and-a-half hours' sleep a day in what she called "slices of about 20, 40 or 70 minutes".

The Solar Impulse pilot is likely to experience "micro-sleeps", nodding off very briefly, which are very dangerous for drivers, says David Ray, professor of medicine and endocrinology at Manchester University. He adds that they're not ideal for monitoring flight equipment either, but not quite as risky.

In an experiment carried out by Nasa, pilots who were allowed to take a nap of 40 to 45 minutes improved their performance by 34% and their alertness by 54%. But this was simply for a standard long-haul flight, rather than being one's pattern of sleep over five days. And it was double the 20 minutes at a time the Solar Impulse pilots will have.

So, does his ordeal pose any long-term dangers? "The risk is primarily that during the five-day trip, during their sleep-deprived state, they make a mistake, that decision-making goes completely out of the window," says Ray. "You can recover after a while, with a few good nights' sleep. But it's not very pleasant."

The answer

• 20-minute naps are arguably too short for a restorative nap

• 30 minutes a time would be better, but 90 minutes allows a full sleep cycle

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