I'd have to say swimming is the best of the three. It's a full-body workout while constantly testing your cardio. It's also great for your core, breathing, etc. Swimming is also zero-impact, whereas running can cause aches and pains, shin splints, and even stress fractures. Cycling can be hard on the knees, especially if there are preexisting knee problems. Of course stress fractures and the like are the more extreme issues associated with running, but you never hear about someone hurting themselves swimming. Unless you slam your heels into the wall during a flip-turn. That shit hurts. Anyway, the safest, and most effective cardio workout in my opinion would have to be swimming.
... to add to that a little, I'd say running is better than cycling if you're training for MMA. There's nothing bad about any of these activities, in fact, I believe it's best to incorporate them all as well as other activities in order to constantly test and push your body in different ways.
Last edited by davidm724; 01-27-2008 at 08:14 AM.