I actually spent some time talking with my Active Release Therapist about this earlier this week. He explained to me that his understanding is this:
Look at the differences in muscularity between Olympic runners who run less than 400 meters, and those who run over 800. The shorter distance sprinters generally have much better muscular development. This is because high intensity bursts near your 100% mark cause a surge of GH in your system that can last for up to 3 hours (that is, if you don't consume a large amount of sugar post-workout) and that extra GH can help increase your muscle size.
High intensity sprinting recruits a ton of muscle all over your body. The core, shoulders, arms...basically everything has to tense to some degree so that you can keep your balance.
What I took from talking with him is that if you're doing sprint work HIIT style, make sure you keep the high intensity segments short enough so that you're exerting at as near to 100% for as much of the time as possible. Usually no longer than 20 seconds for the sprints. I'm sure some people will disagree, and you'll have to be the judge of how well you respond, but my therapist used to compete and he's still a pretty big guy.
I usually get nice and warm, then sprint all out for 12-15 seconds, walk for 30, all out for 12-15, walk for 30. Do this for 5 minutes and I consider it a set. I usually do about 7 sets.
Maybe that will get you started.