Be Happy - Swim

I've noticed when I'm getting to the pool in the morning - about 6:30am - there is a bunch of people leaving who are happier than any other group I meet all day. It's the Masters swim group. They get there at the crack of dawn. Why are they happy? I've had my theories - including it's because their work-out is over. But even the stray person I see when I'm done with my workout - we late risers don't finish as a group - are also pretty content. I came across this article today which talks about the psychological benefits of exercise. Nice read. Enjoy.