Wrong! Endurance cardio will burn muscle as well as fat, but intervals will spare your muscle, for the most part. You do not want to be a flabby muscleman, so get some intervals in.
(Though I still recommend endurance at least once a week. When you're getting big, your heart is working overtime, so you need to keep it in tip-top shape! Or, you could avoid it and have your first heart-attack by the time you're 21!)
