You’re Still Burning Calories Long After HIIT. The Secret Is EPOC and It’s More Powerful Than You Think.

Sure, it takes time to see major payoffs from working out, whether you’re looking to build muscle, lose weight, or improve your general health. But exercise does offer some forms of instant gratification (oh hey, endorphins). Among the best of which is a metabolic boost due to EPOC, a.k.a. the afterburn effect.

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EPOC is the result of ATP production.High-intensity exercises generate a greater EPOC effect than lower-intensity ones.Exercises that recruit fast-twitch muscles are better at stimulating EPOC.Anaerobic exercises lead to a bigger afterburn than aerobic workouts.HIIT produces the highest EPOC effect.It’s unclear how long an afterburn lasts.Steady state cardio produces less of an afterburn

Wondering what is EPOC, exactly? The acronym stands for excess post-exercise oxygen consumption, and it refers to the increased level of O2 your body consumes and calories it burns in order to recover from working out.

Tracy Wehrman, an exercise physiologist at Maximized Potential, likes to tell people to picture EPOC this way: You go on a run with your dog and he suddenly breaks free to chase after a squirrel. “Your casual jog turns into a sprint to catch him. After three minutes, you finally get a hold of the leash again but are exhausted and have to find a bench to sit on and catch your breath.”

If the casual run is your body’s regular state of operation, and the sprint is your workout, then EPOC is happening while you’re posted up on that bench. Now that you understand what EPOC is, here are eight things you should know about it if you want to optimize the EPOC effect of your workouts.

EPOC is the result of ATP production.

On a cellular level, your workouts are powered by a chemical compound called adenosine triphosphate (ATP), which is what essentially supplies the energy necessary for metabolism. “The more ATP [you use working out], the more calories needed to help produce more ATP for recovery,” says Steve Proniewych, exercise physiologist at High Performance Physical Therapy.

Putting in the effort to earn maximum results — LumiNola – Getty Images

High-intensity exercises generate a greater EPOC effect than lower-intensity ones.

“The higher the intensity of the exercises, the harder you will stress the body,” says Proniewych. “This would mean you will need more ATP energy and oxygen after for your body to recover.”

Diverse fitness class doing squats — FatCamera – Getty Images

Exercises that recruit fast-twitch muscles are better at stimulating EPOC.

Fast-twitch muscles are larger and denser than slow-twitch muscles and can generate more force and power with quicker response times. They’re the ones used during anaerobic workouts like HIIT, heavy lifting, and plyometrics. “The larger and denser your muscles are, the more ATP required, which means a higher level of calorie burn,” says Proniewych.

Young woman training with weights — Thomas Tolstrup – Getty Images

Anaerobic exercises lead to a bigger afterburn than aerobic workouts.

Doing workouts that require your body to produce energy without oxygen (anaerobically) as opposed to with oxygen (aerobically) means creates a bigger oxygen deficit in your system that’ll it’ll need to repay during recovery. Plus, anaerobic exercises rely primarily on fast-twitch muscles.

Instructor photographing athlete exercising on jump box in crossfit gym — Cavan Images – Getty Images

HIIT produces the highest EPOC effect.

HIIT has the trifecta when it comes to EPOC igniters: 1. It’s high intensity. 2. It’s anaerobic. 3. It utilizes fast-twitch muscles. Boom! To get the most afterburn, “make sure it’s an exercise that you can push your body as hard as it will allow,” says Wehrman. Here’s a list of HIIT workouts to help you get started.

Attractive Woman doing kettlebell exercise at gym — Cavan Images – Getty Images

It’s unclear how long an afterburn lasts.

More research needs to be done in regards to the length of time EPOC effects the body. Some studies say it lasts only 15 minutes, while others have determined that increased oxygen consumption can happen for several hours. What does ring true is that how many calories you burn post-workout depends is different for everybody and that the real benefit of EPOC is the collective impact of this elevated caloric burn overtime. “People should understand that EPOC is determinant on various factors. Adaptation response will work differently for people and specific fitness levels,” says Abby Rivas, EP-C at High Performance Physical Therapy. So, making sure your workouts are varied, consistent, and progressively challenging are all key to keeping your EPOC effect optimized.

Sweating female boxer drinking water after workout in boxing gym — Thomas Barwick – Getty Images

Steady state cardio produces less of an afterburn

Endurance running, swimming, and cycling, are all great workouts, but they won’t boost your metabolic rate as much as HIIT or resistance training. “Steady-state exercises that are a constant level of intensity for longer periods of time tend to have much lower EPOC effect, which means less calorie burn,” explains Poniewych. This is because the energy you’re expending is being produced using oxygen, meaning it doesn’t much, if any, extra oxygen to replenish ATP post workout—it’s doing it in real time.