I've been hearing two seemingly contradictory things about how you should do cardio training. Some people have told me it is best to accelerate at a healthy pace towards your THR and then maintain it for the remainder of your work out, while other people have told me its best to work out in intervals of varying difficulty (i.e. start easy for two minutes, then switch to very difficult for the next 2 minutes, then medium, then medium hard, etc. for the remainder of the workout). I'm thinking the second option would obviously mean that you are not always maintaining your THR, since you are sometimes over and sometimes under. Am I right? and if so, which is the best way to be doing your cardio?