Although the "Afterburn effect" isn't the miracle fat-loss cure some would have you believe, it's not all hype either. It's a real thing, and makes sense to incorporate into your weight loss and fitness program.
As a result of any exercise, your body burns calories. Some of the calories will be burned during the exercise, while others will be burned afterwards as your body recovers. Simply put, the calories burned afterwards can be referred to as the "afterburn". (Note: it's technically called EPOC: excess post-exercise oxygen consumption, which refers to the fact that your energy expenditure is measured by your oxygen consumption).
What exercises cause afterburn?
Different types of exercise cause different degrees:
- Traditional cardio workouts (i.e. cardio done at a constant moderate pace for a lengthy period) result in minimal afterburn. Plenty of calories are burned during the exercise, but very few afterwards.
- Resistance training (i.e. weight training) and circuit training have a higher degree of after-burn than traditional cardio.
- High intensity exercises in general also have a higher degree of after-burn (whether cardio or resistance training)
- Interval training (bursts of high intensity with very brief rests in between) has a higher degree of afterburn than exercising at a constant intensity. (This mainly applies to cardio, since circuit & resistance training are by necessity interval-based, provided rests are minimized).
So for example, you could increase your afterburn by replacing your regular cardio workout with a high-intensity interval cardio workout.
Or you could replace a low-intensity resistance workout with a high-intensity one.
How big is the effect?
The effect is useful, but not the enormous calorie consumer some would have you believe:
- It's an elevation of a few percentage points above your resting metabolic rate.
- But it can last for anything from a few hours to a day or more.
- Summed over the duration of the afterburn period, this can amount to anywhere between 30 and 150 extra calories burned (or more), depending on the exercise performed.
While these numbers aren't huge, if you're doing it right, afterburn training can add a few percentage points to your daily calorie burn. That adds up over time, and along with all the other little things you're doing to tweak your diet and exercise, will certainly help tip the scales towards fat loss.
Does it let you eat more?
Despite what you may have read ("local guy/gal lost a hundred pounds eating donuts and french fries, because of this one little secret"), afterburn is a minor but useful exercise tweak, and doesn't justify increasing your calorie intake. Alas, no amount of exercise tweaking can provide a free pass for over eating or poor diet. At least, not in my experience.
Does it burn fat?
The metabolic processes involved in energy consumption during afterburn are different from those used during exercise:
- During exercise you're drawing on energy reserves within the muscle & blood stream (basically glucose). You're not (generally) burning fat.
- Afterwards, you're replenishing those reserves, repairing & rebuilding, and have a generally raised metabolism due to hormones released during exercise.
Because your glucose levels are reduced after exercise, your body will draw more on your fat reserves for the energy it needs during the recovery period.
What's unknown or unclear about afterburn?
Actually, it's interesting how much we don't firmly know about the afterburn effect, given how often it's quoted as some kind of miracle training technique ("do thirty minutes of exercise per week, and get awesome six-pack abs while you sleep!!")
Like any scientific research, it's happening gradually and carefully. So while we currently have a decent general picture of what's going on, it will be some time before there's a clear and consistent view of the details.
Here are some factors that aren't currently well understood, and if they are, they don't appear to have filtered into general circulation yet.
- Your gender. There are plenty of biological differences between males and females. Is afterburn affected by them? Maybe not, once differences in lean body size are accounted for (men are bigger than women so burn more energy).
- How overweight you are. This certainly affects your ability to do certain types of exercise. Does it affect how your body's energy consumption reacts after exercise? Or doesn't it matter, so long as you do the same amount of work? Apparently the latter.
- Your level of fitness. Again, this affects the sorts of exercises you can do, and how effectively you can do them. One argument is that the fitter you are, the longer you can sustain intense exercise, and the more effectively you can undertake intense weight training, both of which should result in a greater post-exercise burn. A counter argument is that the fitter you are, the more rapidly you recover, which implies a shorter afterburn period.
- Your age. Age affects some aspects of exercise and physical fitness. Maybe it affects afterburn?
- Your diet. Food obviously has a big influence over biology, but how does it affect Afterburn? For example: apparently caffeine might increase it; while acute dietary restrictions reduce it (which doesn't surprise me - yet another reason not to starve yourself). Will we see a wave of "eating for afterburn" fad diets a few years from now?
- Exercise duration. Yes, if you exercise for a longer duration, you'll generally experience more afterburn. However, increased duration comes at the cost of decreased maximum intensity (you can't sprint a marathon), and it's not clear how the two factors interact with regard to afterburn. Personally, I'm fit enough that I can sustain relatively high intensity interval or circuit training for about 20-25 minutes. I haven't measured my own EPOC (and it would take a carefully designed lab and experiment protocol to do so), so all I can say is that anecdotally I'm happy with the results.
Furthermore, there is no formula to calculate the amount of energy you'll burn post exercise. It would be awesome if you could plug your height, weight, age, gender, fitness level, and some details of your workout into a calculator and be told you'll burn an additional X calories per hour for the next Y hours. But it doesn't exist.
Although we don't know in detail exactly how to create the best afterburn effect, we do know that you can increase your calorie burn if you incorporate high intensity training into your workout routines. As well as creating an effective post-exercise energy burn, this sort of exercise has additional benefits, such as improved strength, endurance and agility. In fact, these are the primary benefits of high intensity training, and afterburn is a nice bonus.