HIIT, short for High Intensity Interval Training, allows you to shorten your workouts while burning fat in a short and intense workout.
It used to be set up at a 2:1 type session. ie. Sprint for 20 seconds followed by a 10 second recovery period and then repeated up to 8 times. This offered a 4 minute high intensity workout (not counting a 5 minute warm up prior to exercise and a 5 minute cool down period after.) A total of 14 minutes, after which you can crawl back to the car and head home.
That is very intensive and most of us are not able to handle that short of a rest period. Not to worry though because you can do a number of variations that work best for you.
Here is an example of a HIIT routine I followed the other day. I warmed up for 5 minutes. Then I ran hard for 20 seconds and followed that with 40 seconds of very lite jogging. I repeated that for 8 sets and then did a 5 minute cool down.
You can, and I often do, run the high intensity runs for longer, for example, 20 seconds, and follow it by possibly a 1 minute low intensity jog. Just keep in mind that the longer the intense run periods are, the less chance you can keep up a sprint type run.
Are you getting the picture? Experiment. Your body will let you know what you can handle.
This is intense and it works. I generally do 2 of my weekly sessions using HIIT and the other 2 aerobic sessions are whatever I feel like doing. Maybe a long slow run for 1 of them and a lesser distant run at a faster pace for the other. Sometimes I feel really energized and do an additional HIIT session.