Igniting EPOC ( Excess Post-exercise Oxygen Consumption ) or afterburn as we know it, translates into a metabolic boost which continues to burn up to 48hrs ( which is why i only teach Mondays Wednesdays and Fridays ) after a completed HIIT routine. Since research and studies show that HIIT helps build Muscle Mass, no muscle cells are depleted and  you actually gain more lean muscle mass which in turn will feed on more calories and boost your Metabolism keeping you fit, healthy and strong.