I've been lifting for about 8 years now, but I've never done much cardio because of my already high metabolism. Now that I'm 30, I'm starting to get a little fluff so I'm interested in throwing some cardio in a couple times a week. My question is, should I do like 15 minutes with my THR up high, or should I drag it out for like 45 minutes but less intense. I'm under the impression that if you keep it short and intense, you burn fat but maintain muscle. If you have long sessions, than your more apt to lose some muscle tissue as well. Any thoughts to this ???? Thanks.