Why Are Sloths Slow?

How fast do sloths actually move? 🦥

Sloths are known for moving slowly — even the word “sloth” by definition refers to someone who’s lazy or reluctant to make a move.

In nature, though, sloths might seem lazy because they’re always in one place, but it’s not so much laziness as it is who they are and how they were born — moving slowly is what makes a sloth … a sloth!

But whyare sloths so slow anyway?

We spoke to Dr. Michael Habib, an expert in animal locomotion, biomechanics and physiology and a research associate at the National History Museum of Los Angeles, to find out why sloths are so slow.

How fast do sloths actually move?

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Commonly found high up in the trees of Central and South America, sloths spend their days lounging around in lush rainforests, occasionally making their way down to the ground for an occasional swim or to relieve themselves (something they only do once a week or so!).

Sloths spend approximately 15–20 hours per day sleeping, so it’s no surprise that when a sloth does get up, she isn’t going very far.

Sloths move so slowly that they only travel approximately 41 yards per day (or the length of half a football field) — and that’s for both types of sloths (two-toed and three-toed sloths).

Why are sloths slow?

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According to Dr. Habib, sloths are slow because of their unique digestive system, muscles and skeleton.

They have a slow digestion

When it comes to why sloths are slow based on how their bodies function, it really comes down to digestion — and it actually takes a long time for a sloth to digest her leafy diet.

In fact, a sloth's digestion is so slow that it takes approximately several days (and sometimes longer) for food to fully pass through her system.

“Most leaf [eaters] deal with this by being large animals, but an alternative is to have a very low metabolic rate and just let the food move through the gut very, very … slowly,” Dr. Habib told The Dodo. “Sloths use this ‘slow lane’ option (so do koalas, though less extreme).”

So because a sloth has an extremely slow digestion and, in turn, a very slow metabolism, she’s going to move very, very slowly.

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They’re built that way

In terms of what makes sloths slow based on how they’re built, Dr. Habib said it’s a combination of a few things:

1. Sloths have low overall muscle mass.

Since sloths are generally not very muscular, they don’t burn as many calories.

2. The muscle that a sloth does have is very slow, highly aerobic muscle.

This means that although she isn’t super muscular, a sloth’s muscles are highly specialized to keep her clinging to trees without a problem.

3. The lever arms on a sloth's musculoskeletal system nearly all favor force output over speed.

This means she’s very strong (three times stronger than humans are!) but not the speediest. In fact, a sloth’s so strong that she’s able to withstand the force of a predator trying to take her from a tree.

4. Sloths very rarely move near their top speed.

“While their top speed is low, it is higher than what we usually see,” Dr. Habib said. “So they seem even slower than they really are.”

So while sloths are slow naturally, one thing’s for sure: They definitely aren’t lazy.