Question

Polar bear needs a lot of rest due to fast in its blubber. Even though swimming required a lot of work, polar bears are able to swim to far away distances. Why doesn't it did overheated due to a lot of work ?

Answer 1

Swimming is not hard work.
It is tough for humans, yes.
But polar bears...they do it easily.

Swimming is easy because polar bears are used to it(adapted) .
They have large blubber. Blubber is fat. Oil and fat floats in water, right?.
So, if polar bear jumps into water, it can float easily without moving a muscle. Also, it just needs to give a small push to move forward in water.

So, for polar bears, its easier to swim, than to walk actually.

When a polar bear is walking, it has to carry it's full weight on its legs. This is very hard because they have huge weight and walking in snow is never easy.

But in water, their entire weight is supported by water. So, for polar bears, its easier to swim.

So, they never get tired of swimming. But when they walk, they need more energy, and they need to rest to prevent overheating.