Do you know if there are any animals which exercise with an intention to become fit or maintain fitness?
well im a biologist, i was lurking on this theme a bit and it results that some animals have the capacity of learn from the predecessors the knowledge of hunting, just like us, this is pretty palpable on marine mamals like killer whales and dolphins, they teach theyr pups how to hunt, but we have the case of the octopuses, they have to learn all the knowledge by theyr own bc theyr mother dies when the eggs pops but they are pretty smart animals, can be compared in intelligence as a domestic cat.
Just to resume, every animal improves theyr capacities focused in one special feature, like in this case, hunting.
Humans just improves theyr bodies to aesthetics features, involving reproduction and social status, but this, is just falls straight in the culture of the society they are living. Culture are the limit where the animal kingdom and the humanity separates, so improving aesthetic features are just a human thing, animals can do this in a primitve way but a human can make big changes based on the needings of the social needings, like "if you are fat girls will just think you are a ghost" meme.