Why do short burst sprints work?

[big E]

Ive been doing 10 minute shortburst sprints for cardio, fatburning for awhile now with great success 3 times a week. 30 second walk 30 second sprint while always raising the speed on sprints till i get to 12 mph for 30 and then cooldown. What loses me is why this works so well when I'm not getting to the 15-20min standard where fatburning truly begin, s.

ATP-CP is used in the first 30 seconds
Lactic Acid System takes over at the 30 second mark and uses only carbs/glucose/glycogen
3 minute mark Krebs Cycle takes over fully.

[JPM]

Try doing a search on the Tabata method of training for fat burning and athletic endurance training.  There are other systems along this line of short burst or  Interval training. Very productive for results and the all important time management vs energy spent. Good Luck. 

[dontknowit]

It's the afterburn that makes HIIT so effective.
Your hart keeps pumping at a higher rate, without actually doing something.

[kicker]

Ya, I also heard that this type of training keeps your metabolic rate up.  Kinda like weight lifting but the mechanism/physiology behind it is different.  Any conditioning experts or kinesiologists out there that can elaborate on this?