Sloth Muscle
Sloth movement is different from many other mammals — you can see that by the way they move so slowly from limb to limb of the trees, high up in the canopy.
For sloths, only 25 to 30 percent of their body weight is muscle. In most mammals, muscles make up 40 to 45 percent of body weight. Since sloth digestion is so slow, much of the time a large proportion of their body weight is made up of undigested food matter or waste product that they have not yet gotten rid of.
Sloth muscle also tends to react slower in comparison to other animals. On the other hand, it can stay contracted much longer. That allows it to move slowly and stay in one position for a long time without tiring.
That fixed sloth-smile look that sloths have comes in part from this minimized muscle mass in combination with their fur markings. Sloths don’t have the muscle capacity to make lots of facial movement, like many humans and some other animals do. Instead, their ‘facial expression’ comes from the fixed image of their fur markings. Movement of the face is reserved for the mouth and nose, which do the job of perceiving scent and taking in food.
What a cute look!
