Anyone who has performed a HIIT workout will be familiar with the term “The Afterburn Effect”.
This is the metabolic process which is triggered by explosive sprint-based training, and legend has it you’ll burn calories at an accelerated rate for several hours after your workout is over.
But how longer are we talking?
And how many more calories will it help you burn?
Well, it depends who you ask. Some “experts” claim that doing as little as 20 minutes of HIIT can help you burn double your usual calorie expenditure for up to 24-48 hours (!), meanwhile other “experts” claim this phenomenon doesn’t exist at all!
So settle down with a protein shake, Uncle Russ is gonna clear this one up for you!
The Science Behind “The Afterburn Effect”
The technical name for this process is EPOC (excess post-exercise oxygen consumption), although I’m sure you’ll agree that “The Afterburn Effect” sounds much cooler!
It’s a phenomenon which occurs in response to explosive sprint-style training, such as HIIT (high intensity interval training) or weight training, and it’s 100% a real thing.
(Phew!)
When we perform regular cardio (aerobic cardio) we generally do so at a low intensity for a long period of time (e.g. 45 minutes on a stationary bike or treadmill) and the body will use fat as the primary source of fuel for your working muscles.
When we swap this out for training at a higher intensity (e.g. HIIT) the body switches to using carbohydrates as it’s primary fuel source for your muscles, and this also triggers the EPOC response.
So the key difference here is the net calorie burn. You can achieve quite an impressive number in 45 minutes of aerobic cardio but the calorie burn will end as soon as you climb off the bike (or treadmill), whereas with a HIIT workout you might burn a little less during the actual session but you’ll continue to burn calories at an accelerated rate long after your leave the gym.
Make sense?
Great!
Also, the more explosive nature of workouts which unlock EPOC tends to lean to better performance-related benefits and a higher retention of lean muscle tissue, which is why athletes like sprinters and weightlifters fucking love it.
How Many Extra Calories Does “The Afterburn Effect” Help You Burn?
This is where much of the confusion lies, because people are full of shit.
I often see personal trainers bumping their numbers in a bid to sell programs, like this:
“For every 500 calories you burn in the workout, you’ll burn an extra 500 calories at home!”
This pisses me off because it’s absolutely not true.
A great 2006 meta-analysis (a study which looks at the whole body of research on the a particular topic) published in the Journal of Sports Science showed that EPOC will help you burn roughly 6-15% more calories than you burned in the actual workout. (1)
With that in mind, if you burned 500 calories in the gym then you could expect this to climb around 575 calories in the hours that follow the workout.
The researchers also suggested that they believe most people are incapable of training hard enough to unlock the full benefits of EPOC, because the results at the top end of the scale were all achieved by experienced trainees. They had this to say:
“The optimism which was shown in earlier studies regarding EPOC and weight loss appears to be unfounded, and this is reinforced by the fact that the exercise stimuli required to produce prolonged EPOC is unlikely to be tolerable for most individuals.”
– Journal of Sports Science
How Long Does “The Afterburn Effect” Last?
This is another area of confusion, because trainers often pump up their numbers in an attempt to win client from their rivals.
For example, a gym up the road from me has an advertisement in their window which claims that you’ll continue burning fat for 30 hours (!) after your workout ends – and they also believe that the first few hours of EPOC will have you burning as much as 600 calories per hour!
Not to be deterred, another “boot camp” decided to run a similar campaign where they suggest that their special HIIT workouts will unlock a 48 hour afterburn effect, and that you’ll be burning 800 calories per hour for the first few hours of that!
So let’s look at some actual science, shall we?
Be warned; the numbers are a lot less sexy!
A detailed study published in Medicine & Science in Sports & Exercise back in 2011 confirmed that EPOC typically lasts around 14 hours. There has never been an instance of it going past that point, but there have been some instances where it didn’t last that long (e.g. shorter HIIT workouts where the trainee didn’t quite maximize their training output). (2)
So don’t believe the bullshit!
Knowing This, Why Is HIIT Still Considered “Better” Than Regular Cardio?
HIIT offers us a couple of important benefits which regular cardiovascular training does not.
- The workouts are shorter
- It’s better for improving explosivity
- You’ll get superior muscle retention
These two things along are great reasons to be doing HIIT on a regular basis, but if your primary goal was purely the calorie burn then you could achieve largely the same results via traditional aerobic cardio, it would just take longer.
For that reason I hate seeing people bash regular cardio, because it’s 100% better than no cardio at all, and it offers almost the same fat loss benefits as HIIT!
A 2017 meta-analysis published in Obesity Reviews showed that the total calorie burn via regular cardio and HIIT is almost identical, it’s just the structure that’s different; e.g. traditional cardio will have you working at a moderate intensity on a machine for 45-60 minutes, whereas HIIT will have you going “all out” for 20-30 minutes followed by a period of up to 14 hours where you burn calories at an accelerated rate. (3)
This means from a calorie burning perspective you can take your pick. I like to mix them up on a regular basis, depending how I’m feeling on the day and how much time I have available.
However, when we look at the other training benefits HIIT provides, the gap in quality becomes significantly wider and we can see why most athletes love doing HIIT.
A study from the University of Tasmania discovered that HIIT workouts can be used to make significant improvements to explosive power output, sporting performance, and VO2 Max (the most recognised marker of cardiovascular fitness), so this makes it a great choice for an athlete looking to stay in peak condition. (4)
Furthermore, I’m sure you’ve heard the old saying that “Cardio will kill your gains, bro” in the gym before?
Well, a 2011 study published in the Journal of Strength and Conditioning Research showed that HIIT actually has no negative effects on hypertrophy or strength when paired with a weightlifting program, whereas traditional cardio shows a reduction of around 30% hypertrophy and 15% strength. This tells us that the more explosive nature of a HIIT workout makes it perfect for hanging on to our hard earned lean muscle mass!(5)
It is these two things, rather than “The Afterburn Effect”, which are the real reasons why HIIT is such an effective training method, because if someone can notch roughly the same (or maybe slightly better) calorie burn while also improving their explosive power output and a higher degree of muscle retention, it creates a better environment for the person to build a great body.
Anyway, I hope that erases all of the confusion surrounding the afterburn effect. Yes, it’s a real mechanism, and sure it can help you to lose weight – but it’s not the “Holy Grail” of fat loss which some people make it out to be!
References:
- LaForgia, J., et al. Effects of exercise intensity and duration on the excess post-exercise oxygen consumption. J Sports Sci (2006).
- Knab, A. M., et al. A 45-minute vigorous exercise bout increases metabolic rate for 14 hours. Med Sci Sports Exerc (2011).
- Keating, S. E., et al. A systematic review and meta-analysis of interval training versus moderate-intensity continuous training on body adiposity. Obes Rev (2017).
- Driller, M. W., et al. The Effects Of High Intensity Interval Training In Well Trained Rowers. Int J Sports Physiol Perform (2009).
- Wilson, J. M., et al. Concurrent Training: A Meta Analysis Examining Interference Of Aerobic And Resistance Exercise. J Strength Cond Res (2011).