Sunday, October 21, 2018

Sprint Intervals and the Afterburn Effect

Sprint intervals, a form of High Intensity Interval Training - HIIT, are no joke.  Each interval may be short, but you're working at between 80-90% of your maximum effort, which means that in less than 20 minutes you'll be left gasping for breath.  Endorphins aside, it's not a great feeling.  But that gasping for breath actually has an incredibly positive side effect - EPOC, also called the afterburn effect.

What is EPOC?

Excessive Post-exercise Oxygen Consumption is the term given to your body's response after exercise as it works to recover your resting level of metabolic function (called homeostatis).  Your body needs time to recover and cool down, the same way a car does after it's been driven.  

While it's recovering it's going to burn calories as it works to replenish oxygen stores, remove lactic acid, repair your muscles, replenish ATP, and restore your body temperature.  HIIT also stimulates production of Human Growth Hormone (HGH).

How long does EPOC last?

Studies of the EPOC effect show vary in their results, with some claiming the effect can be noticed up to 72 hours after a HIIT session.  However, most studies note that the effect peaks within an hour of completing the exercise session, and tapers off within 16-24 hours.

The rate it tapers off, and the amount of calories burned during this period, are primarily effected by the intensity of the exercise.  The more intense the session, the higher the amount of calories burned, which isn't that surprising.  However, it also appears the the length of the exercise is not a major factor in the length of the EPOC effect.  

How to Maximize the EPOC Effect

As long as the HIIT session is at least 15 minutes, and at a high intensity, the effect is measurable and higher than when compared to a steady-state cardio session.  One study found that sprint intervals doubled the number of calories burned after exercise due to EPOC when compared to a normal jogging session.  Another found that a higher intensity workout produced the greatest afterburn effect.

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