HIIT is a anaerobic activity designed to burn twice the fat in half the time of aerobic activity. Studies done by Tabata and Tremblay et. al. have shown HIIT to be more effective at burning fat and maintaining muscle mass than traditional aerobic activity. In a study done by King et. al. HIIT increases resting metabolic rate for the following 24 hrs due to excess post-exercise oxygen consumption and may improve maximum oxygen consumption better than long aerobic sessions. That means HIIT will speed metabolism up like a mexican gerbil on crack - maybe not that much but, significantly more so than sitting on a treadmill watching Opra for an hour every day.
Here’s how it works. Warm up for 4 to 5 minutes

doing whatever you like. If you choose to run then you will sprint for 30 seconds for the high intisity interval then slowly jog for 1 minute for a low intensity interval. This is a 1:2 high low interval. Do this a total of two times the first week and add one high low interval each week up to 15 intervals. Always cool down for 5 minutes and stretch. Perform HIIT 2 to 5 times per week. HIIT can be done in any way whether on a bike or swimming or a kayak or running ect. just alternate in a 1:2 high low interval. If done on training days, then always do it after weight training as doing it before can actually have a negative effect. If done before weight training, you will begin to break down muscle tissue for energy during weight training. For more challenging intervals use a 1:1 high low interval. meaning sprint for 30 seconds and jog for 30 seconds. This will be much more challenging but, will be just as, if not more, effective and shorter. Consult a physician before starting this or any other program on this site.

Here is an example of the first and second week.

Warm-up: jog for 5 minutes
Sprint for 30 seconds
Jog/walk for 1 minute
Sprint for 30 seconds
Jog/walk for 1 minute
Cool down: walk/slow jog for 5 minutes then stretch
Total time = 13 minutes

Warm-up: jog for 5 minutes
Sprint for 30 seconds
Jog/walk for 1 minute
Sprint for 30 seconds
Jog/walk for 1 minute
Sprint for 30 seconds
Jog/walk for 1 minute
Cool down: walk/slow jog for 5 minutes then stretch
total time = 14.5 min