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.