Calorie Afterburn - What is EPOC?

How many calories do we burn after (rather than during) a workout? The afterburn effect is called EPOC (Excess Post-exercise Oxygen Consumption) and the name alone confuses people - what the hell has oxygen consumption got to do with calorie burning? Well... Those nerdy guys in labs measure calorie expenditure by measuring oxygen consumption. They will hook you up to some breathing apparatus and if you had an elevated metabolism (e.g. after a workout) you would be consuming more oxygen than if you had a lower metabolism (e.g. after 9 hrs sleep).

There is lots of scientific information and research available on this topic, I'll link you to a few things that you might like to check out but generally I'm going to try and cut through the science and summarise it all for you.

Lower intensity exercise gives minimal afterburn: Most research shows that low-moderate intensity exercise has a minimal afterburn effect, and you need to work at around 70% of your maximal effort (as a minimum) to generate a decent afterburn. In fact EPOC doesn't really take hold until you are training at 85%-100% of your maximal effort.
To be clear - low intensity exercise (e.g. walking) is still beneficial, and is worth keeping in your weekly training regime. You can't train at 85%-100% every day, so lower intensity exercise is important to keep you active and has some health benefits.
In terms of calorie burning, one hour of brisk walking might burn around 350 Cal and would have very little afterburn effect. So walking is useful for staying active & burning some calories, but isn't intense enough to fire up a big EPOC response. Even moderate exercise like continuous jogging is found to deliver minimal afterburn.

Resistance exercise works, but... Lifting weights gives a strong afterburn effect if you follow these simple rules:
1. Big muscle groups, compound movements... Bicep curls and other isolation exercises are out!
2. You must work to failure, or at least very close to failure.
3. Minimal rest times between exercises, and between sets. In fact a circuit style workout with no rest between exercises will probably give the greatest afterburn effect.

An investigation into afterburn following resistance training also showed that the majority of afterburn calories were in fact coming from fat burning. The study showed that fat burning was 75%-105% higher than normal resting levels.
I highly recommend dynamic/plyometric exercises to get maximum muscle recruitment and fatigue. For this reason I like kettle bell swings, box jumps, jumping lunge, sprints, stair running, power cleans etc. although for beginners perhaps stick to compound free-weight exercises.

When doing cardio, stick to intervals. Most studies indicate that High Intensity Interval Training (HIIT) gives a stronger afterburn effect than traditional running or cycling.
The mistake most people make here is not working hard enough during the intervals. HIIT training should be incredibly hard, it makes you feel sick, you want to give up, it hurts. This is where the PT earns their money because very few clients would have the motivation to do intervals on their own and thus they could never achieve great fitness and/or fat loss results on their own.
HIIT should involve a 30sec-2min gut-busting (near maximal) effort, followed by a low intensity "recovery" period (traditionally this is called 'Fartlek'). Beginners should start with short efforts. It's also important to set the right work:rest ratio for clients, beginners will work at around 1:3 whilst more advanced trainers will work at 1:1 or perhaps even harder. Beginners might start with only two or three intervals, but gradually build up to an advanced volume of around ten intervals. HIIT can be done on a treadmill, bike, rower or at the local park so it's easy to mix it up for variety.

How big is the EPOC effect? Each study is slightly different and reports different results. One recent study conducted on men in a metabolic chamber (so it should be very accurate) shows that participants burned 519 Cal during a high intensity 45 minute cycling workout. Following the workout, on average metabolic rates stayed elevated for 14hrs, giving an afterburn of 190 Cal above normal resting levels.
These numbers are significant, remembering that you have to walk briskly for one hour to burn about 350 Cal. Compare that to the high intensity cycling workout - 519 Cal plus a bonus afterburn of 190 Cal, you get a total benefit of 709 Cal from just 45 mins of exercise - more than double the one hour walk.

Another study focussing on resistance training in women showed that metabolic rate was elevated by 13% above resting levels for three hours following a high intensity workout, and was still 4% above resting levels 16 hours after the workout.
Just think about how an extra 100-200 Cal from afterburn will add up if you train clients like this three times per week over a 3-6 month period.

So... How does it work? For those interested in the science of how this works, I recommend you read this article which gives a nice overview of the mechanisms behind EPOC.
In a nutshell, training at very high intensities causes a massive metabolic and cellular disruption to our body. It freaks out our systems, muscles and cells. In particular the hormonal response from HIIT and intense resistance training sparks a stronger afterburn effect - studies appear to indicate higher release of epinephrine, norepinephrine and growth hormone (all fat burning hormones) which gives fat burning a real kick-along following an intense workout.

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