but if HIIT uses fat stores for energy (as opposed to carbs), is that fat coming from an equal distribution of the body (typical of weight loss) or from around the muscles that are being taxed?

Logic tells me that during my high intensity spurt on a bike, it would not be efficient for my body to grab some fat stored in my upper arms or gut (for example) but instead would be going for the fat stored closest to the muscles being worked.

I would love to hear your opinions on this - and just so you know I am NOT trying to lose weight/fat in my hips or butt, but this occurred to me after I got through with my HIIT and my legs were just wiped out.

Dont think about the muscle involved in the exercise. The "energy" has to travel in to the blood stream first.

HIIT uses carbs,once your heartrate gets above a certain level you burn carbs "sugars" etc.