This may sound too good to be true, but it's legit: During an intense workout, your body needs to shuttle enough oxygen and nutrients to your muscles. And when you stop moving, it doesn't automatically go back to its normal metabolic function.
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Rather, your body needs some time to return to its natural state, and actually demands more oxygen to do so, which in turn burns more calories. This is called the afterburn effect or excess post-exercise oxygen consumption (EPOC).
Here's everything you need to know to understand EPOC and harness the power of the afterburn effect to apply it to your own fitness goals.
What Is the Afterburn Effect?
EPOC is the amount of calories you burn above your resting metabolic rate following exercise, explains Jason Stella, a certified performance enhancement and corrective exercise specialist and national education manager at Life Time Fitness.
"While you do burn a lot of calories during your workout, workouts that create EPOC allow for an increased amount of calories, especially from fat, typically peaking within 45 minutes, and can extend up to 24 to 48 hours," he says.
Stella notes that there are two categories of workouts that elicit a great afterburn effect: high-intensity interval training (HIIT) and high-intensity steady-state (HISS) training.
Most people are familiar with HIIT workouts, but Stella believes many are actually doing HISS workouts and calling them HIIT. HIIT involves intervals of all-out, maximum effort followed by a longer recovery so that you can maintain that max effort during the work periods. On the other hand, HISS is when you exercise at a high intensity and rest only as long as you need to in order to complete each repetition with proper form.
"Both HIIT and HISS are better than doing moderate-to-low-intensity, steady-state cardio workouts," Stella says. Unlike steady-state cardio, which relies on your aerobic pathway (with oxygen) to produce adenosine triphosphate (ATP) — the fuel for your muscles — HIIT and HISS workouts rely on both your anaerobic (without oxygen) and aerobic pathways for ATP.
Stella says anaerobic pathways can't supply ATP for long, so you can do high-intensity work for only a short period of time. Once that ATP runs out, it's necessary to exercise at a lower intensity or take a rest interval to replenish it, which allows the aerobic pathway to kick in to supply more ATP.
This creates an oxygen deficit, which enhances the afterburn effect, because your body will need more oxygen from the aerobic pathway to restore ATP and rebuild muscle proteins.
Your body also requires more oxygen to go back to its normal metabolic function after intense exercises like HIIT and HISS. So within the 24 to 48 hours after your workout is over, your body continues to work to get more oxygen, and in this process, burns calories.
According to the American Council on Exercise (ACE), your body expends approximately 5 calories of energy for every liter of oxygen it consumes. The greater demand for oxygen post-workout known as EPOC means you'll burn more calories overall.
Everyone will generate a different afterburn effect, depending on your fitness level, the intensity and duration of your workout and factors outside of your control, like how your blood is circulating and how your body breaks down and uses fat while working out.
Because the factors that contribute to the afterburn effect vary so much between people, there isn't enough definitive research yet to help quantify exactly how many more calories you burn due to EPOC versus how many calories you burn during exercise in general.
However, EPOC from a HIIT workout can increase total calorie burn by 6 to 15 percent, per the ACE. If you burned, say, 350 calories from your workout, you may burn up to an additional 53 calories due to the afterburn effect. Again, this is only a rough estimate; the calories you burn after exercise depend on your fitness level and other factors.
The Benefits of the Afterburn Effect
You'll Burn More Calories Without More Effort
Of course, the most eye-catching benefit of EPOC is the idea that you'll burn calories, even at rest. And to maximize your calorie burn for each minute you spend exercising and afterward, HIIT and HISS are the way to go.
According to a March 2015 study in the Journal of Strength and Conditioning Research, you can burn more calories during a 30-minute HIIT session than spending the same amount of time doing a steady-state cardio session. Unlike steady-state cardio, HIIT and HISS often incorporate strength-training elements, which can help you build more lean muscle.
The more lean muscle you have, the more calories you'll burn, because muscle is metabolically active, meaning it burns more calories at rest than body fat. While doing cardio will definitely help you burn calories, strength training not only burns calories during exercise but also helps you build muscle, which contributes to overall calorie burn.
There's still a time and place for low-intensity steady-state (LISS) cardio, like jogging and cycling, especially if you enjoy it, like on days when you want to take things a little easy and allow your muscles to recover.
You Can Do Shorter Workouts
"Even though the workout time is shorter [during HIIT], since EPOC increases exponentially with exercise intensity, the short exercise bouts generate more EPOC than the longer, moderate-intensity workouts," Stella says.
You Might Lose Weight
HIIT and HISS exercise may amplify the effects of EPOC compared to the same amount of time you would spend doing lower-intensity exercise, aiding your weight-loss efforts.
A June 2017 review in Obesity Reviews suggests that three weekly sessions of HIIT can help reduce overall fat mass and waist size in people with obesity and overweight as much as moderate-intensity training, which requires more time.
You Could Improve Your Sports Performance
Incorporating some HIIT and HISS into a program to help improve sport-specific performance not only reduces your training time, but it can also give that performance a boost.
A July 2016 study in the Journal of Sports Sciences found that HIIT training helped rowers improve more than lower-intensity, long-distance training. When the rowers included two HIIT sessions in the mix of 10 weekly workouts, they saw greater gains in performance than when they did 10 weekly aerobic sessions.
How to Apply the Afterburn Effect to Your Workouts
How do you know if you're working hard enough for EPOC to happen? Trainers advise using a scale called rate of perceived exertion (RPE), with one being the lowest rate of effort, aka lying on the couch, and 10 being a flat-out sprint.
An RPE of seven is the intensity you want to aim for in order to start up the afterburn effect, Stella says, with an RPE of about three during a rest interval. The higher you go from there, the more EPOC you create, and the shorter your workout can be, he says.
Fortunately, there are many ways to practice HIIT and HISS, outside of the usual interval formula of 30 seconds of work and 30 seconds of rest.
Tabata training, for example, is a four-minute workout consisting of 20-second, max-effort intervals and 10-second rest periods. Given this work-to-rest ratio, it would be considered a HISS workout, not HIIT, Stella says, due to the limited amount of rest and heart rate recovery. You can tack on Tabatas to the end of your cardio or strength workout to increase your afterburn power.
If you crave a little more variety in your HIIT workouts, consider HISS-style circuit training, in which you do an ordered list of exercises at a set number of reps and rounds. In circuit training, you'll do exercises back to back and recover 30 to 60 seconds between sets. The beauty of circuit training is that you can target multiple muscle groups in one session.
The type of workout you choose will come down to personal preference, but they'll have the same effect overall, Stella says. He suggests doing HIIT twice a week — not on consecutive days — and balancing it out with regular cardio and non-heavy strength training on other days.
5 Types of HIIT and HISS Workouts to Spark EPOC
- Tabata: Do an exercise for 20 seconds at maximum effort, then rest for 10 seconds. Repeat for four minutes.
- Every Minute on the Minute (EMOM): Do a set number of exercises at a specific rep range as quickly as possible at the start of every minute and rest for the remainder of the minute.
- As Many Rounds as Possible (AMRAP): Complete as many rounds as possible for a set of exercises with a specific rep range in a given amount of time.
- Circuit Training: Do a series of exercises that target different muscle groups back-to-back and rest for 30 to 60 seconds between circuits.
- Ladder Workout: Perform 10 reps of an exercise for the first round, then 9 reps for the second round and continue to work your way down until you do one rep. Then, rest for 30 seconds before climbing the ladder again.
Try This 8-Minute Workout to Increase EPOC
Try this HIIT body-weight workout designed by Stella to increase your calorie-burning potential. Complete as many rounds as possible within eight minutes, resting as needed, and track the total number of rounds you complete. Each time you perform the workout, try to beat your previous total.
- Squat: 6 reps
- Push-Up: 4 reps
- Burpee: 2 reps
- Chin-Up: 1 rep
All exercises should be done with perfect form. Rest whenever you need to, but for only a short period until you can continue the exercise with good form.
Move 1: Squat
- Start standing, feet hip-width apart.
- Extend your arms out in front of you and slowly bend your knees as you push your hips back to squat down. Focus on lowering your body as if you were going to sit on a chair.
- Squat down until your thighs are parallel with the floor, or as low as you can go comfortably while maintaining good form. Your knees should be over your toes and your gaze should be straight ahead.
- Pause for a moment at the bottom of your squat.
- On an exhale, reverse the motion by pressing through your heels to return to standing. As you stand, lower your arms back to your sides.
Move 2: Push-Up
- Begin in a high plank with your core, quads and glutes engaged. Your shoulders should be stacked over your wrists and your hips should be in line with your head and heels.
- Bend your elbows to about a 45-degree angle from your torso and lower your body toward the ground.
- On the way down, squeeze your shoulder blades together.
- When your chest hovers just above the ground (or however far down you can go), press into the ground and push your shoulder blades apart to return to the starting position.
Move 3: Burpee
- Stand with your feet hip-distance apart, then squat down and place your hands on the ground between your feet.
- Jump your feet back into a high plank with your shoulders stacked over your wrists.
- Then, jump your feet back to the outsides of your hands.
- As you stand up, press down on your heels to jump up with your arms overhead.
- Land softly on the ground with your knees slightly bent.
Move 4: Chin-Up
- Grip a pull-up bar comfortably yet firmly with both hands, palms facing your body and shoulder-width apart.
- Using your arms, back and core, think about driving your shoulders and elbows down while pulling your body up until your chin is above the bar.
- Lower back down with control until your arms are straight.
More HIIT Workouts to Reap the Benefits of EPOC
- American Council on Exercise: "7 Things to Know About Excess Post-exercise Oxygen Consumption (EPOC)"
- The Journal of Strength and Conditioning Research: "Caloric Expenditure of Aerobic, Resistance, or Combined High-Intensity Interval Training Using a Hydraulic Resistance System in Healthy Men"
- PLOS One: "Twelve Weeks of Sprint Interval Training Improves Indices of Cardiometabolic Health Similar to Traditional Endurance Training despite a Five-Fold Lower Exercise Volume and Time Commitment"
- Obesity Reviews: "The Effects of High‐Intensity Interval Training vs. Moderate‐Intensity Continuous Training on Body Composition in Overweight and Obese Adults: A Systematic Review and Meta‐Analysis"
- Journal of Sports Sciences: "HIIT Enhances Endurance Performance and Aerobic Characteristics More Than High-Volume Training in Trained Rowers"