Tell Me About HIIT for REALLY BIG GIRLS

If you mean genuine HIIT (not just any old interval training with the label hung on it...) then suggest you start with getting the opinion of your Doctor first.

IMHO if you are "really big" then build your fitness and endurance first with something far less taxing.

I waited to respond, hoping that someone with a stronger background in HIIT would jump in, but let me give you my "any old interval training" suggestions.

Basically, find a low impact exercise you like and go hard for a short period (let's say 30 seconds if you really want a number) and then rest for a period (let's say 120 seconds but more about periods later).

I have recently rediscovered the elliptical for interval training. I crank the resistance up and fight my way through 30 seconds and then take the resistance down to very little. But you could also use the treadmill to fit your fitness level, using big inclines or speed for the intense portions. You could get similar results outside by sprinting, jogging or power walking for the intense part, or finding yourself a hill to go up and down. A bike outside or a stationary bike would work for this too, as would a rowing machine. I'm thinking you could even race swim/float on your back. I've used the stairs in my home for this too.

I'm trying to improve my VO2 at the moment, so I push hard enough that I am gasping for air at the end of those 30 seconds. Personally, I don't time the recovery portion, but on average it's at least 120 seconds; it tends to get longer as my cardio session goes by. From the little I've read, shorter recovery periods and longer intense portions are for very fit people only.

But the best exercise is exercise that makes you happy. If you don't like it, "reasons" to skip it are going to come up.