What is Afterburn

Afterburn is known as excess post-exercise oxygen consumption (EPOC). It refers to the oxygen your body needs to restore itself to the pre-workout state. Your body uses oxygen to produce fuel ( ATP) needed for your muscles to fire up during exercise, but it can also call on stored energy sources that don't require extra oxygen. HIIT workouts typically utilize the latter more so than steady-state exercise, and will also require more oxygen post-sweat session( oxygen and calorie burn go kind of hand in hand after exercise). How many calories afterburn(EPOC) actually burns?

Your body continues to burn calories after a workout, it's usually only 6 to 15 percent of the total calories you burned while exercising. So if you burned 300 calories during your workout, your afterburn would only be about 18 to 45 

calories. 

Is it true that we can only achieve afterburn effect from HIIT?

EPOC is not limited to HIIT workout.It's present after all aerobic exercise but the level of exercise intensity does play a role in just how many calories your body burns post-sweat. 

For low-intensity activity like a treadmill jog, you can expect a lower afterburn effect (about 6 percent calorie burn but with HIIT workouts and things like Tabata,you could reap an afterburn closer to that 15 percent.

What else attribute to afterburn?

There are a few other factors that alter your individual afterburn rewards for an example weight, fitness level, type of diet,muscle mass etc all play a role.

Does after burn last for 24 hours?

People who are more physically fit may derive longer benefits from the EPOC effect, it's usually only up to a couple hours definitely not 24hours.After all we're just ordinary humans