“Afterburn” is a popular buzzword in the fitness community — especially where fat loss is concerned.
So, what is it? Afterburn is another name for a physiological effect known as excess post-exercise oxygen consumption (EPOC).
In a nutshell, afterburn, or EPOC, refers to the amount of oxygen your body needs post-workout to get you back to your normal, pre-workout state. It also helps account for the fact your body continues burning calories long after your workout is over. Or at least, more calories than you normally would. So, for anyone interested in fat loss, know that EPOC may help you achieve the caloric deficit you need to budge the scale.
THE LOWDOWN ON EPOC
When you exercise, your body burns calories by consuming oxygen, which allows your muscles to keep working, says Rosie Reilly, facility leader, trainer and nutrition coach at Fit Body Boot Camp in Berkley, Michigan. Depending on the intensity, duration and type of exercise, your body also uses a certain amount of muscle glycogen (quick-acting carbs) and adenosine triphosphate (ATP) for fuel. You’ll also experience a rise in body temperature, as well as breakdown of muscle tissue.
Fast-forward to the end of the workout: You’ve put the weights away, turned off the treadmill or otherwise moved on to the next part of your day. You may be done exercising, but your body now faces a different kind of workout: Restoration and recovery.
“Once you complete your workout, your body doesn’t immediately go back to resting level,” Reilly says. “It is still in a heightened state.”
Think of your body after exercise like a car after a drive. Once you turn off the engine, the hood of the car is still warm to the touch. Your car remains warm until all the heat is released and it’s able to return to its normal resting temperature. “Our bodies do the same thing post-workout,” Reilly says.
To return to its normal resting state, your body uses oxygen to replace the ATP and muscle glycogen you used during your workout, restores oxygen levels in the blood, lowers your body temperature and works with protein to repair any damaged muscle tissue. The more oxygen it takes to restore your body, the more calories you’ll burn post-workout.
How long your caloric burn stays elevated post-workout depends on your age, gender, lean body mass, as well as the intensity of the exercise you did. However, research published in the European Journal of Applied Physiology suggests EPOC can last up to 72 hours.
Unfortunately, it’s hard to know exactly how much afterburn you’ll produce from any given workout. “Since [EPOC] is a measure of the oxygen you consume, and not heart rate, you can only measure it inside a lab,” says Andrew Mariani, a trainer at the HIIT-focused fitness studio Fhitting Room On Demand.
That said, there are some general guidelines that may help you identify the best workouts and strategies for achieving maximum afterburn.
HOW TO BOOST AFTERBURN
If you want to achieve high levels of EPOC, your best bet is to focus on the intensity of your workout. “Generally, short and intense training sessions like HIIT can produce more EPOC per minute of exercise than steady-state training like distance running,” Mariani says.
One classic HIIT formula is known as the Tabata protocol alternates 20 seconds of all-out exercise with a 10-second break for eight rounds. Popular exercise options for this workout include sprints on a treadmill or stationary bike, but you could also do burpees, jump rope, kettlebell swings or dumbbell thrusters (hold a pair of weights at your shoulders and squat down; press the weights overhead as you stand). Keep your intensity high, but choose exercises you’re comfortable with. In other words, don’t do sloppy burpees for a Tabata workout.
Keep in mind you may end up burning the same number of total calories (or even fewer calories) from a HIIT session as a long, steady-state run; it all depends on the intensity, duration and type of exercise.
For example, one small study in the February 2014 issue of Applied Physiology Nutrition and Metabolism found a 20-minute HIIT session burned just as many calories over a 24-hour period as a 50-minute steady-state session. The HIIT session involved 10 rounds of 60-second intervals on a stationary bike at roughly 90% maximum heart rate, with 60 seconds of active recovery between each round. Meanwhile, the steady-state session consisted of cycling for 50 minutes at approximately 70% maximum heart rate. So, if your only concern is how many calories you’re burning from exercise, you may save time with a HIIT routine.
Also, since HIIT is — by definition — intense, limit the number of sessions to three per week to give your body adequate recovery time. Make sure you’re pairing your exercise program with smart nutrition strategies to help your body recover and ensure you continue burning more calories per day than you consume. “Without nutrition locked-down, the effects of EPOC will only take you so far,” Reilly says.
If fat loss is a secondary training goal, you can still encourage your body to burn more calories post-workout without committing to HIIT. Incorporate a few sprint or hill intervals into a steady-state run or bike ride, shorten the rest periods between resistance exercises or add a workout finisher once or twice per week. (Read more about finishers here.) “Short, quick bursts of work, combined with short rest periods will be the key,” Reilly says.