Sloths have comparably long arms, but very short shoulder blades and a very narrow chest.
The researchers argue that these features help to maximize mobility at the shoulder.
They also help these creatures navigate around the rainforest and between trees, a complex three-dimensional habitat, without being able to jump between gaps.
Sloths also have a special arrangement of muscles.
One of the pectoral muscles, those that human athletes would use to bench press a weight, for instance, descends down to a sloth's lower arm.
A video radiograph of a moving sloth
In other mammals, including people, it is usually attached at the upper arm near the shoulder joint.
This peculiar arrangement helps sloths carry their own body weight, which is always being dragged to the floor by gravity.
"And of course they have hook-like claws and other things as well," says Mr Nyakatura.
These adaptations all help sloths lead their unusual lifestyle.
"Actually this strategy opened a niche for them," explains Mr Nyakatura.
Sloths move so slowly because of their low-calorie food.
Being able to survive just on leaves means they can avoid the need to seek out high-calorific food such as meat of fruit, more energetic behaviour that in turn might attract the attentions of predators.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.