Sloths, the lazy creatures famed (and envied) for their slow-paced, laidback lifestyle manage to spend most of their time hanging upside down because their internal organs are quite literally fastened in place, scientists have discovered.

The lethargic creatures can take up to a month to digest a single leaf, sleep for at least 10 hours a day and can only climb at a leisurely maximum speed of eight feet per minute.

The tree-dwellers head to the forest floor to go to the toilet just once a week, leaving scientists pondering how they are able to breathe with the full weight of all that waste matter pressing on their lungs.

Download the new Independent Premium app Sharing the full story, not just the headlines

At any one time, a third of a sloth's bodyweight is taken up by stored urine and faeces, making their stomach and bowel contents extremely heavy.

But scientists at the University of Swansea have now deduced that after spending 90 per cent of their lives hanging upside down, sloths have evolved 'attachments' in the abdomen.

Shape Created with Sketch. Eight things you didn't know about sloths Show all 8 left Created with Sketch. right Created with Sketch. Shape Created with Sketch. Eight things you didn't know about sloths 1/8 There are two main types of sloths - two-toed and three-toed (but even the two-toed have three toes on their hind legs). REUTERS/Juan Carlos Ulate REUTERS/Juan Carlos Ulate 2/8 Only the two-toed variety (left) can live in zoos, as they have a varied diet. Other sloths are more particular, only eating certain trees and thus making them more expensive to look after. RAUL ARBOLEDA/AFP/GettyImages 3/8 Sloths mate and give birth in the tree-tops, with the baby sloth clinging to its mother for the first nine-months of its life. WALTRAUD GRUBITZSCH/AFP/Getty Images WALTRAUD GRUBITZSCH/AFP/Getty Images 4/8 Sloths can live for as long as 40 years, although eagles are one of their main predators. Their only defence against the birds is to stay very still and blend in with the vegetation. Creative Commons/Kansasphoto 5/8 Sloths are prefectly adapted to a a life in the tree-tops, with long arms and hooked claws perfect for hanging off branches. Their grip is so good, they've been known to stay suspended from branches even after death. CARL DE SOUZA/AFP/Getty Images 6/8 Sloths don't sleep as much as people think. Wild sloths sleep about 10 hours a day, although even when they're awake they tend to stay very still. REUTERS/Fredy Builes 7/8 Three-toed sloths can turn their head 270 degrees. They have up to three extra vertebrae to allow this. REUTERS/David Mercado 8/8 Mega-sloths once roamed the earth. A genus of ground sloth named Megatherium existed up tilll around 10,000 years ago in South America. It was six metres from head to tail and weighed as much as four tonnes. Thankfull,y it was also a herbivore. Creative Commons/Ballista 1/8 There are two main types of sloths - two-toed and three-toed (but even the two-toed have three toes on their hind legs). REUTERS/Juan Carlos Ulate REUTERS/Juan Carlos Ulate 2/8 Only the two-toed variety (left) can live in zoos, as they have a varied diet. Other sloths are more particular, only eating certain trees and thus making them more expensive to look after. RAUL ARBOLEDA/AFP/GettyImages 3/8 Sloths mate and give birth in the tree-tops, with the baby sloth clinging to its mother for the first nine-months of its life. WALTRAUD GRUBITZSCH/AFP/Getty Images WALTRAUD GRUBITZSCH/AFP/Getty Images 4/8 Sloths can live for as long as 40 years, although eagles are one of their main predators. Their only defence against the birds is to stay very still and blend in with the vegetation. Creative Commons/Kansasphoto 5/8 Sloths are prefectly adapted to a a life in the tree-tops, with long arms and hooked claws perfect for hanging off branches. Their grip is so good, they've been known to stay suspended from branches even after death. CARL DE SOUZA/AFP/Getty Images 6/8 Sloths don't sleep as much as people think. Wild sloths sleep about 10 hours a day, although even when they're awake they tend to stay very still. REUTERS/Fredy Builes 7/8 Three-toed sloths can turn their head 270 degrees. They have up to three extra vertebrae to allow this. REUTERS/David Mercado 8/8 Mega-sloths once roamed the earth. A genus of ground sloth named Megatherium existed up tilll around 10,000 years ago in South America. It was six metres from head to tail and weighed as much as four tonnes. Thankfull,y it was also a herbivore. Creative Commons/Ballista

These attachments work by anchoring organs in place such as the liver, stomach and bowel and prevent them weighing down on the diaphragm.

The team's findings are published in the Royal Society journal Biology Letters.

Rebecca Cliffe, one of the University of Swansea scientists who conducted the research at the Costa Rica Sloth Sanctuary, said: “For a mammal that spends a significant amount of time hanging upside down, this large abdominal weight pressing down on the lungs would make breathing very costly in terms of energy, if not impossible.

"Sloths have solved this problem by anchoring their organs against the rib cage. They have multiple internal adhesions that bear the weight of the stomach and bowels when the sloth hangs inverted.

“They generate just about enough energy from their diet to move when and where required, but there is not much left in the tank afterwards.

"It would be energetically very expensive, if not completely impossible, for a sloth to lift this extra weight with each breath were it not for the adhesions. The presence of these simple adhesions therefore really is vital."

Co-author Professor Rory Wilson, also from the University of Swansea, said: "Nothing that sloths do is normal. They are quite the most extraordinary and 'off-the-wall' mammals I have ever come across and yet we know so very little about them."