HIIT/ morning cardio question + Pre Meal

If I do HIIT in the morning for cardio and I eat a protein meal with 0 carbs. I read that your only supposed to do HIIT 2 times a week, and I already did it today after school. So I was wondering what kind of cardio I can do that is muscle sparing for my morning work out tommarow right after waking up and eating a no carb protien meal. Any Ideas?

If you are in shape, the twice a week thing is BS in my opinion.  If you ever played sports, like I did, hockey, football, basketball, soccer, these are all HIIT workouts, especially the soccer.  I would do these, in a league, at least 4 nights a week in high school and still be able to hit the gym.  If your meals are carb free, make sure they have good fats to replace them.  Your body operates best on one of these 2 fuel sources.