That goal to burn fat begins by putting pressure on your systems. The up-and-down speeds you experience in high-intensity interval training strain your cardiovascular and respiratory systems—and for good reason.
Your body adjusts to these stimuli. As you work harder and harder, your body will improve its functions to match. In the process, you burn fat and lose weight. That matches your goals, right? So keep working: Walk, jog, and sprint. You'll reach your goals.