A few of my buddies at the gym have started giving me greif because I usually do 20 minutes of cardio on the stairmaster each day of my 5 day after lifting. They tell me that I'm burning energy that should be used for bulking, though I do it mostly to keep my heart in shape and because I feel great afterwards. Are they right? Should I nix cardio if I am trying to put on more muscle? Would I be better off just doing something like jumprope in between sets to keep my heart rate up?