When we exercise hard or long, or both, we use the body’s resources in certain ways in order to achieve this level of performance. Glycogen (glucose) in muscles and liver is used up, lactic acid builds up in muscles, muscle gets damaged and broken down for energy, other energy systems are exhausted. It’s a demolition job and repair is required when you finally stop exercising. Oxygen is the driver of this process, and without it being supplied at the level that can drive your intensity of effort, you slow down and even stop — exhausted. Yet oxygen is also the driver of the repair process.
Anaerobic exercise causes oxygen debt
The body has a way of enduring for a few minutes when it really has insufficient oxygen for your exercise needs. This is called anaerobic exercise. You know when this is happening because you start to get out of breath and slow dramatically. This can only go on for a few minutes at top effort.
However, after you stop, your body then tries to get everything back to normal. To do this, it uses oxygen in the repair and replenishment process and to repay the debt — more than it would normally if you had not exercised that day or for as hard or long. This increased oxygen use is called “excess post-exercise oxygen consumption” or EPOC. It’s sometimes called “afterburn”, which is not a bad way of thinking of it. Short term oxygen debt recovery happens just after you stop and until you get your breath back. Longer-term EPOC continues for several hours, perhaps more than 12 hours, until glycogen is restored, lactate is removed and muscle is repaired and replenished by amino acids.
How EPOC can help you
EPOC often gets discussed in terms of weight loss programs because the excess oxygen use stimulates metabolism and, theoretically, it’s good for weight loss, which is probably true, except it’s not all a bed of roses stimulating EPOC, and it’s not necessarily the best option.
The thing is, you have to work hard for the afterburn effect. You need to exercise at high intensity or for a longer time at moderate intensity. EPOC occurs when you degrade body systems and use resources. A brisk 30-minute stroll around the block with the dog or a leisurely chat and pump at the gym and a nice cup of coffee in between won’t do it either. You will read in various places how EPOC only comes from high intensity exercise. This is not necessarily true. There is likely a minimum amount of work to be done, but no one really knows what this is. It could just as easily result from moderate intensity cardio for a longer period of time. You can probably do it lifting weights, running sprints or running for an hour, but in the end, you have to work hard whatever you do.
EPOC versus energy consumed during exercise for weight loss
It’s no use doing lots of high-intensity intervals for 20 minutes, exhausting yourself, then expecting EPOC to make you thin like a cheetah after you stop. You also have to consider how much energy (calories) you expend during the exercise. While the interval training might be time efficient, you’re probably not going to burn the same calories during that exercise as the guy or gal that runs for an hour at 5 minutes/kilometre pace (8 minute/mile) pace. EPOC can’t make up for an imbalance of calories burnt during exercise.
The best exercise program for weight loss
Stop worrying about the afterburn. (As if you ever did.) Mix your training up with weights, aerobics, and sprint or interval training if you feel fit enough for it. Read more in my article: The Best Fat Loss Strategy That Really Works.