I had success with HIIT as part of the Body for Life program when I was in grad school. I just recently started doing HIIT again to boost my fat loss (and I would prefer a short 20 minute intense workout over an hour long moderate workout any day). Here's my program on the elliptical:

3 minutes warm up

1 minute high speed

2 minute medium speed

Repeat 3 minute cycle 4 times (total of 15 minutes)

Cool down 2 minutes.

My heart rate gets as high as 170 and in the 140s during my medium speed. I love doing this.

So what program are you guys doing and have had success with?

I've done it running at the track and on a stationary bike. I warm up for about 5 minutes with brisk walk or slow jog. Then usually I will do 90% to all out sprint for about 20-30 seconds, then about 40-50% of max speed for about 1-2 minutes. Then I repeat all of that for around 20 minutes, and make sure I never do it for more than half an hour. But that's just me wanting to preserve my muscle, so everyone has different goals. I only do mine once or twice a week, the rest of my exercise is lifting 4-5 times a week.

I am new to it. I searched the intenet and came up with the following. I read to not do it too often as it wears you out - so twice a week is what I have been doing so far.

Eliptical:

5 min warmup

5 minutes of intervals -15 seconds ALL OUT/45 seconds normal aerobic speed/intensity - repeat for a total of 5 times. By the 4th or 5th repeat I am feeling it because I really do go "all out" for those 15 seconds!

5-10 minutes of normal aerobic intensity, no interval

5 minutes of 30 seconds high intensity/30 seconds of normal aerobic intensity - repeat total of 5 times. I can't sustain this at 100% effort, but the high intensity burst at probably 80-90% of my maximum still brings that heart rate way up

5 minutes of cooldown

I then do about 30 minutes of strength training.