I'm considering taking up swimming as my primary form of cardio. Right now I run because it's convenient and all I need is a pair of shoes. However, on my way home from work, I have the ability to hit a pool and, if I keep a swim bag, I could make the switch pretty easy. On one hand, swimming would definitely help with my new passion other then then martial arts, surfing, but I am wondering if it will be enough. Does anyone have any experience with this? Does anyone swim for their cardio and do very little running? Maybe a combo would be good?