jostpuur: Of course people work out to be good looking. Otherwise it would be a total waste of time.
To be good looking can be the reason for some, but it's not the only possible reason.
I go jogging regularly mainly because I feel it is a useful skill to able to run (you never know when you need the skill. It's like self defense skills: You are unlikely going to need them, but you never know if the need suddenly comes at you), and in a hope that I'm going to live a little bit longer with a strong heart than with a weak one.
Sometimes people can also be interested in numbers like how many push ups or pull ups one can do, or how much one can bench and so on. In sports spirit. It's not awfully different from being interested in school grades. That's about basic interest in one's own abilities.