RE: The best way for me to cut.
genon, HIIT is not 30sec sprint 30sec jog and repeat.
HIIT is about going all out [100 MHR] for as long as possible, then go at a lighter intensity until you can sustain that DURATION OF TIME at your MHR again.
bear in mind that although on the second, third etc etc phases of MHR the actual speed you run/sprint/swimm/whatever will be a lot slower than the previous time. speed does not matter, its duration at MHr tht you want. and i'm not suggesting anything here, if you play american footy you will be quite fit anyway i presume, but GA is right, to have an effective workout using HIIT [20mins ish] you will hae severe difficulty in resting for 30seconds in between sprints.
if i were you i would go for something like this:
MHR 30sec [say sprinting 200m up hill]
40-55%MHR for 1-2min [walking/v.light jog back down]
repeat for 20min even if by the end of it you MHR[sprint speed] is reuced to a crawling pace. you can either decrease the rest periods bit by bit, or, as i prefer, up the MHR periods as and when you feel you need to so that by the endyou are going flat out for 1+minutes and resting for 2min.