Do any top level fighters swim to work on their cardio? I've always thought that swimming would be a great low-impact way to train the heart and lungs. But I never hear about it. I guess I was thinking about this back when Rampage was coaching TUF and had his 250lb guys running for miles on end. I thought I heard it caused some damage to the knees of a few guys... (this true?) And just wondered, why not swim? Its a great aerobic activity. And with guys like Shogun having exceptional conditioning, but knee problems wouldn't it just be a given? Or do they already do this?