Odd Things I Think About

There's a poster in the staff area at work: "930 Things to Be Happy About: A Stream-of-Consciousness List." One of the things listed is: Healthy exercise or a swim at the Y. So this has me wondering just how the author defines exercise. By having the modifier "healthy," she is saying there is unhealthy exercise as well. And a swim at the Y does not qualify under the heading "healthy exercise" or it wouldn't have to be listed separately. So how do I know if my exercise is healthy or not and why is a swim at the Y a happy thing even though it's not healthy exercise?