I'll give my 2 cents worth of ideas from experience, none of which are science based.
I have a few questions regarding cardio. Is it true that it catabolizes muscle? Some say yes, some say no, some say only if done in excess, like what endurance athletes do. I've even heard some say it wont happen unless excess fat stores are used up first. I'm inclined to believe the third opinion - only if done in excess.
From my experience, number 3- excesse cardio, but in addition to that, a lack of calories. Once you burn through the carbs and fat only protein is left to burn. So eat up!
Is there a recommended amount for optimal health? The only opinion I've heard on this is that of couch-to-5k, who claim 30 minutes of moderate intensity exercise 3 times a week is optimal for cardiovascular health. Then again, I suppose with more volume I do, the better cardiovascular I'll need, which will probably exceed the amount necessary to live a high quality sedentary life, right?
I really can't recomend what would be a good amount. Almost every where you look, some say 20-30 mins a day others say 2 hours a week.
I'm interested in doing HIIT, as most sources say it is superior to constant, moderate intensity workouts(and it sounda a helluva lot more interesting), but I'm concerned about overtraining my legs, as I am doing squats 3 times a week and deadlifts 1-2 times a week at low rep, high intensity(Starting Strength). If I shoud do HIIT, should I increase my low intensity phase along with my sprint phase, or should I keep my low intensity phase at the lowest setting, so I can go all out during the sprint phase? If I slow down during the last 5-10 seconds of a sprint phase, should I lower the setting I use for it?
HIIT is great, but rememebr there are other ways of getting cardio instread of running- i.e. swimming, rowing (a concept 2 is great), sled dragging (although not as fast as the others because your dragging a 70+ pound sled, gets your heart rate up in a hurry). You can also throw in "Finishers" at the end of a strength workout. Here are some good ones http://www.t-nation.com/free_online_art ... o_burn_fat
Good luck, glad to see that you are cautious about over doing. Better to be on the safe side, and slowly build up by doing short stints at first, maybe less then 10 mins and go from there.