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Stand on your head. Don't ask questions. Just do it. Now take some deep breaths. Not so easy is it?

Yet sloths spend 90 per cent of their lives upside down and, unlike humans, it doesn't affect their breathing.

And now scientists have worked out why.

Sloths: The ponderous creatures, which spend 90 per cent of their lives upside down, have internal organs fastened in place to prevent them squashing their lungs, a new study from Swansea University has claimed

A Swansea University-led research team has found that sloths can accomplish 'upside-down breathing' because their internal organs are anchored by unique adhesive substances in their abdomen.

This prevents the organs weighing down on their lungs.

The research, produced in collaboration with the Costa Rica Sloth Sanctuary, will help scientists understand the elusive and endangered creatures, which are famed - and named - for their languor.

Sloths spend long hours hanging from branches by their hind legs to reach young, tender leaves and are one of the least-studied mammals in the world.

The notoriously torpid animals can take weeks to digest a single leaf and can store a third of their bodyweight in urine and faeces - meaning the stomach and bowels are extremely heavy.

The mystery Swansea's team set out to solve was why this extra weight does not affect their breathing when upside down.

They found that the animals have unique abdomen adhesions which anchor organs such as the liver, stomach and kidneys, stopping them pressing on the diaphragm and hindering their breathing.

Rebecca Cliffe, one of the authors of the paper, is a PhD researcher in zoology at the College of Science at Swansea University.

The intrepid 24-year-old has spent more than a year examining sloths first hand in the spider-infested jungles of Costa Rica.

'Trekking through the jungle is never easy,' she said. 'As well as heat and humidity, I have to be on constant guard for snakes, spiders and scorpions that could cause me some serious problems if I accidentally get too close.

'And then there are the huge swarms of angry mosquitoes that no amount of repellent will deter.

'This all quickly fades into insignificance though as soon as I manage to spot the sloth I am looking for, it's a really great moment that immediately makes everything worthwhile.'

Breakthrough: Rebecca Cliffe, 24, one of the authors of the paper, is a PhD researcher in zoology at the College of Science at Swansea University. She has spent more than a year examining sloths first hand

Speaking of the findings, she said: 'With slow metabolic rates and a low-energy diet, sloths are experts at saving energy and have solved the problem of breathing upside down by anchoring their organs against the rib cage.

'We estimate these adhesions reduce a sloth's energy expenditure by 7-13 per cent when hanging upside down.'

Professor Rory Wilson of Swansea University supervises Miss Cliffe's research and is joint author of the paper. He said: 'Nothing sloths do is normal.

'They are quite the most extraordinary and "off-the-wall" mammals I have ever come across, yet we know so little about them.

'How foolish we would be to watch these creatures become victims of deforestation and habitat fragmentation without having the slightest idea how to help.'