EPOC, or excess post-exercise oxygen consumption, is informally known as ‘the afterburn effect’ and refers to the physiological phenomenon in which your body continues to burn extra energy even after your workout has ended.

It almost sounds too good to be true, even to experts. You’re no longer putting exercise demands on the body, yet your metabolism and muscles and heart are still pumping as if you were? ‘Theoretically, it’s not something you might expect,’ says J Luke Pryor, associate director of elite athlete performance at the University at Buffalo’s School of Public Health and Health Professions. What’s more, the EPOC effect gets hyped up a lot (that group fitness instructor who raves about how you’ll keep ‘torching calories’ long after class ends).

But EPOC is indeed real. Your muscles, heart rate and metabolism are all plugging away at higher rates for quite some length of time after you stop exercising. And if you understand the way EPOC works, it’s possible to structure your sessions accordingly and get more bang for your buck from this internal simmer. So keep reading - and we’ll tell you what is known right now about the mysterious EPOC effect and how best to harness it.

What is EPOC?

To understand EPOC, you first need some basic knowledge of your internal workings. When you breathe in oxygen, your body moves some of it from the lungs into the blood, Dr Pryor says, so the muscles can use it in the conversion of energy for exercise.

You have some stored energy the body can tap immediately, but there’s not enough oxygen straight away. ‘When you start exercising and feel terrible, that’s due to an oxygen deficit,’ says Abbie E Smith-Ryan, an associate professor, director of the Applied Physiology Laboratory and co-director of the Human Performance Center at the University of North Carolina at Chapel Hill in the US. ‘Once oxygen metabolism kicks in, you feel better and more energised,’ she explains.

And the higher your workout ranks on the intensity scale, the greater the amount of O2 you need to take in… and the more calories you burn. Following certain workouts (read: intense ones), ‘the body continues to consume higher oxygen volumes once exercise has stopped’, says Dr Pryor. That’s EPOC in action. Your body is essentially working overtime to recover. ‘Your body needs to reset and get all of its processes back to baseline,’ says Jill Kanaley, a professor and the interim chair of nutrition and exercise physiology at the University of Missouri, US. ‘That means bringing your breathing and heart rate back to resting, lowering body temp, starting to repair muscle fibres and scrambling to replenish your energy stores – which is hard work that requires energy to accomplish.’ Just how much fuel it uses is up for debate

Measure the burn

Our bodies, metabolisms and hormones are all vastly different, so EPOC energy consumption can vary considerably from person to person. The exact amount of time EPOC lasts is hard to pinpoint, Dr Pryor says. But generally, the more oomph in a session, the further your body gets from baseline and the greater the effect you’ll experience.

FYI: there’s both a fast and a slow phase with EPOC. In the fast phase, your body is quickly bringing your heart rate and other vitals back to normal after you first stop exercising – but it lasts for only about three minutes, Professor Kanaley says. The slow phase, in which your body recovers and operates with slightly higher energy needs than usual, can go on for a long time. ‘How long, depends on the intensity and duration of exercise,’ says Professor Kanaley. Some research only monitored EPOC for 30 minutes after exercise; other studies measured effects that lasted up to 72 hours.

In terms of calories, it’s probably ‘a few hundred’, Professor Smith-Ryan says, adding that the number depends on the exercise intensity and other factors such as body composition and diet. It’s also pretty much impossible to get your exact EPOC stats if you’re not in a lab – existing estimates come from sophisticated tech used in sports medicine studies.

Assuming you don’t have a fully functioning sports science lab in youe spare room, you just have to assume it’s happening to some extent. Up to 100 calories per day is a solid estimate for a normal workout, for anywhere from 12 to 24 hours – with the higher end (around 300 calories) possible with very intense exercise.

Apply to life

One hundred calories may not seem like a life-changing number (think: a banana). But if you’re exercising regularly, that small amount adds up over time. ‘Even if EPOC were only a few calories per hour, and that lasted for 12 hours, you might burn an extra 60 to 100 calories really by doing nothing,’ Professor Kanaley points out. If your goal is weight loss, you need a caloric imbalance, and EPOC nudges you in the right direction. But Professor Smith-Ryan (and other fitness experts) tend not to incorporate it into a client’s suggested calorie deficit number because it’s an uncertain amount.

The bottom line: EPOC is a bonus to an otherwise beneficial workout that is likely moving you closer to your goals, says Professor Smith-Ryan. Plus, knowing it’s on the other side of an effort might give you more motivation to push through and crank it up when you need to. A win-win.

The food factor

You’ll burn more calories and fat if you eat something pre-workout (versus doing a fasted session). And if your pre-run snack contains protein you’ll burn even more. One serving of protein had a greater EPOC effect than 90 calories of carbs, found Professor Smith-Ryan’s research. ‘It’s also better for fat metabolism,’ she says, adding that the pay-off is more prominent for women.

A few factors seem to be at play here. Protein is thermogenic (it requires more heat – or energy – to process), it impacts insulin in a positive way and it also provides the amino acids your body needs to get a headstart on the recovery process, Professor Smith-Ryan says. Fuelling up also simply helps you push harder than if you’re running on empty – which means you’ll feel better and be able to manage a more intense workout and, as a result, increase EPOC.

Obviously, you don’t want to eat too much protein before a run or you risk digestive issues, so try something like a small protein shake a good 45 minutes before you set off.

The best sessions to turn up the EPOC

Fiery workouts amp up your heart rate and body temp, so there’s more recovery work to be done afterwards. (Note: also why rest days are crucial.) ‘The simplest way to think about intensity is the talk test,’ says Dr Pryor. ‘You want to not be able to hold a conversation while you exercise.’ These sessions get you to that point:

20 mins of HIIT

High-intensity interval training is generally recognised as an efficient way to boost EPOC. This can be a session that pairs bursts of sprinting with active recovery at a much slower pace.

A heavy-weight circuit

Another motivator to do your strength work. Choose 10 exercises that, in total, work your whole body. For each move, use the heaviest weight you can lift for 10 reps. Do 10 reps of each, making the eccentric (lowering) phase of your reps 4 secs long.

Incline work

Increase the gradient on your treadmill or add hill sprints to a run to challenge both your muscles and cardiovascular system even more.

Resistance running

Do high knees using a resistance band (wrap it around your waist and anchor it to something solid) or side shuffles with a weighted vest for a bigger EPOC pay-off

Running on soft surfaces

Taking your feet to plush ground, such as sand, requires more muscle contractions to maintain the same pace, Dr Pryor says. ‘Essentially, you become less efficient and more energy is expended.’

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