Long-Term Fat Loss: Is the Afterburn Effect Burnt Out?

“Bro, have you heard about the Afterburn Effect? Basically, if you work super hard you can get your body to burn tons of fat even long after you’ve finished training. It’s how all these big guys stay lean.”

This is literally a phrase I heard in a gym while I was training a few years ago. I remember thinking to myself that I’ve heard of that effect before and I had never looked into it much. I knew what EPOC was (excess post-exercise oxygen consumption) and that is a real thing, but can you actually burn a significant amount of calories that would lead to fat loss or at the very least the maintenance of fat loss long-term?

Let’s find out!

Weight Loss Maintenance
You’ve probably been training for a decent amount of time, and once you do you start to realize that achieving goals is one thing; holding onto them for long periods of time is a whole other animal. It’s true that when it comes to muscle mass, it takes far less volume to maintain it than it does to build it (I’ve covered volume thresholds for hypertrophy in a previous article) [1]. However, do the same rules apply to fat loss?

If we’re talking about long-term weight-loss maintenance in the general population, success, as it’s defined by the American Journal of Clinical Nutrition, is losing 10% of initial body weight and keeping it off for at least 1 year [2]. If you’re in the field, maybe you’ve had clients that have difficulty with weight-loss maintenance, or maybe you’re having trouble with it yourself. In either case, we might look to training techniques as a way to improve our chances without making huge changes to diet – and this is where we might run into some problems because:

The Type of Training Matters
The word intensity gets thrown around a lot and depending on who you’re speaking to it could mean anything from weight used, to how fast your heart is beating, to even just your general perception of the workout. Personally, if we’re in the context of weight lifting, the intensity will always mean the load you are lifting. For circuit training and various forms of HIIT, then I’ll replace that with the percentage of max heart rate.

So let’s talk about high effort, high HR intervals. This would be the obvious choice for the afterburn effect considering how much you need to push yourself to remain at consistently high output. That leads us to a study by Kelly et al. that tested two cardio-based HIIT workouts and their effects on energy expenditure and resting energy expenditure (this is the one that matters for afterburn).

Both groups completed a HIIT cardio workout with one group performing the workout for 10-minutes and the other for 40-minutes. In terms of total energy expenditure and resting energy expenditure post-workout, the results favored the longer duration workout which is not surprising, but that REE increase amounts to a measly 92.9 extra kcals burned [3].

Definitely not the long-lasting calorie scorcher we’re looking for here.

Alright, Let’s Get Jacked Instead
Well, I’m glad cardio intervals weren’t the answer here because now that saves me from having to do them. Besides, the more muscle you have the more calories you burn right?

A study by Hunter and colleagues researched just that in elderly participants. The reason I prefer this study population is that in most cases they already have inadequate muscle mass which means we can potentially observe significant changes. These folks were training 3x/week and getting yolked! The average increase in fat-free mass was 2kg while losing 3.4% body fat within 26 weeks.

Not bad at all.

The researchers measured REE before and after the study was complete and found a “significant” improvement in REE totaling a whopping 81 kcal extra burned per day [4]. That’s maybe half a hard candy – nowhere near enough to get these grannies and grandpas in speedo-shape (though that rarely stops them).

You know what, maybe they just weren’t working hard enough. They were pretty old, and I like to work way harder than that!

Push it to the Limit
I know what you’re thinking – your lifting workouts are way harder than cardio intervals or what those seniors were doing during their sessions. Where are the alpha workouts?

That’s where good ol’ Hackney and colleagues come in to save the day. They know what you want and they’re going to give it to you: an all-out savage lifting workout. It might not be exactly what you’re used to, but they included two groups of participants (trained and untrained) as well as incorporating eccentric tempos, multiple movements per set, and long sessions. We know these sessions were grueling because they also measured creatine kinase levels post-workout which is a direct measure of muscle damage and most of these guys were into very high levels, especially in the untrained group.

The results indicated a very high increase in REE even 72 hours after the workout which would be exciting, however, if you have read my previous article on training to failure [click here!] you can already suspect that there’s more at play here than simply creating enough extra calorie burn to reduce body fat. As the authors put it:

“Prolonged elevations in REE between 24 and 72 hours post-exercise may be triggered by factors associated with DOMS and the overall muscle-repair process. … The extent of the elevation was more pronounced in the UT group, indicating a greater degree of muscle damage.” (Hackney et al. 2008)

So, that spike in energy expenditure is due to your body working overtime in order to recover and remodel muscle tissue from the damage the workout caused.

These results are in line with a 2012 paper by Paoli et al that tested high-intensity resistance training versus traditional training in resistance-trained men. These guys were already decently advanced since the average body fat percentage was 8.5% (but I’m not very confident in that number). This training was a rest/pause style training so the participants were using intraset pauses to be able to lift a heavy weight many more times than they would have been able to without the rest. The results showed a solid 452 kcals/day extra that were burned post-workout.

However, while the results are impressive, the authors concluded the same outcome as Hackney and colleagues; the large increase in REE was more than likely because the post-workout re-synthesis of protein is very energy expensive [6].

Final Word
You can never go wrong with wanting to do more work, and no one can fault you for trying to get away with as much as possible in terms of results. We all want to live in a world where we can go to war in the gym and have the resulting effects of that workout continue for a day or two. In some ways they do – but not in the way that we used to think. That being said, here’s what we’ve learned:

Pure cardio-based workouts will burn more calories during training than weightlifting will, but any increase in energy expenditure afterward is minimal and subsides within an hour. While age-related decreases in fat-free mass reduce energy expenditure, increasing the total amount of muscle mass within realistic values doesn’t seem to have a significant effect on increasing REE. What does seem to have the biggest effect on increasing REE post-workout for up to several days is a large amount of muscle damage – the two downsides to this in my opinion are 1) You would have to live in a constant state of debilitating soreness, and 2) your body is too good at adapting to stimuli that you would run out of ways to create that damage. There is also the law of diminishing returns to think about.

There is definitely more room for research to be done on this subject. The studies that are presently available do not all measure REE the same way which can also lead me to wonder if they’re using certain methods in order to confirm their hypotheses.

Finally, I think this is just another way to confirm that there is no perfect workout method. In terms of impressive results, nothing will beat progressive overload, consistency, and eating for your goals.


References:
[1] Bickel, C. Scott, James M. Cross, and Marcas M. Bamman. “Exercise dosing to retain resistance training adaptations in young and older adults.” Medicine & Science in Sports & Exercise 43, no. 7 (2011): 1177-1187.
[2] Wing, Rena R., and Suzanne Phelan. “Long-term weight loss maintenance–.” The American journal of clinical nutrition 82, no. 1 (2005): 222S-225S.
[3] Kelly, Benjamin, James A. King, Jonas Goerlach, and Myra A. Nimmo. “The impact of high-intensity intermittent exercise on resting metabolic rate in healthy males.” European journal of applied physiology 113, no. 12 (2013): 3039-3047.
[4] Hunter, Gary R., Carla J. Wetzstein, David A. Fields, Amanda Brown, and Marcas M. Bamman. “Resistance training increases total energy expenditure and free-living physical activity in older adults.” Journal of applied physiology (2000).
[5] Hackney, Kyle J., Hermann-J. Engels, and Randall J. Gretebeck. “Resting energy expenditure and delayed-onset muscle soreness after full-body resistance training with an eccentric concentration.” The Journal of Strength & Conditioning Research 22, no. 5 (2008): 1602-1609.
[6] Paoli, Antonio, Tatiana Moro, Giuseppe Marcolin, Marco Neri, Antonino Bianco, Antonio Palma, and Keith Grimaldi. “High-Intensity Interval Resistance Training (HIRT) influences resting energy expenditure and respiratory ratio in non-dieting individuals.” Journal of translational medicine 10, no. 1 (2012): 1-8.