The Orange Theory: How Accurate is the “after-burn”?
The Confusion with EPOC: Is the 36 hour after burn just a sales pitch?
We’ve all heard about it, if you’re and avid exerciser or have some sort of routine as far as cardiovascular fitness, you know about high intensity interval training , otherwise know as HIIT training. There are people who believe that it is the answer to all fat loss/ weight loss challenges for the sole idea of EPOC .
What is EPOC?
EPOC(excess post-exercise oxygen consumption), is the process of an increase in oxygen uptake above resting levels after training or exercise. This process requires energy so EPOC translates into burning calories even after an exercise/ training session bout. The purpose of EPOC is to get the body back into the resting state. And, create physiological adaptations from that bout of training/ exercise, which will prepare and help the body to manage the same amount of exercise stress more easily in the future.
HIIT fanatics will claim that your metabolism and the amount and rate at which you burn calories is elevated for up to 36 hours, otherwise know as the “after-burn”. This idea is quite misleading to the general population because they’re not getting the entire story. So, the questions that arise would be as follows; Is the increased 36 hour after-burn accurate? And, Is utilizing HIIT better for fat loss than continuous cardio? The mythical assumption of EPOC is this:
the higher the intensity for a given distance or time, the greater increase exponentially in the magnitude of EPOC (Borsheim&Bahr). For example running 5 km in 20–25 minutes has a larger EPOC effect than running the same distance in 45–50 minutes.
If you used this logic, HIIT intervals performed at higher intensities than continuous cardio would exhibit a higher EPOC effect. But, what about the number of calories burned after each type of training? HIIT versus continuous. Does one burn more calories than the other?
In three studies participants were found to have burned the similar amount of calories in the hours after training through HIIT and continuous cardio(Hazel et al., Skelly et al., Williams et al.). The difference is that the HIIT group took 20 minutes to attain this calorie utilization where the continuous cardio group took 30, 50, 60 minutes. So, one might argue — “there you have it, HIIT is more time efficient than continuous cardio. However, the argument/ question initially wasn’t whether HIIT was more time efficient, it was whether HIIT burned more calories after each session. And, the answer in comparison to continuous cardio is no.
Further analyzing the Skelly study for the sake of practicality. The study measured energy expenditure by having participants breathe through a mouthpiece, and their exhaled air was tested to measure oxygen consumption to calculate their energy expenditure. The air expired was collected every few hours over a 24 hour period including one full hour when participants exercises or rested.
During that hour they either:
- rested for the entire hour
- rested for 10 minutes and cycled for 50 minutes continuously at a moderate intensity.
- rested for 40 minutes and then did 20 minutes of 10 x 60 second high intensity cycling intervals with 60 seconds rest between.
The following data is the average number of calories burned during exercise:
Rest: 125 calories
50 minutes cycling: 547 calories
20 minute intervals: 352 calories
Calories burned over the full 24 hours including the exercise period:
Rest: 3005 calories
50 minutes cycling: 3464 calories
20 minute intervals: 3368 calories
As the data shows that there is only about a 100 calorie difference between the 50 minute continuous cycling and the 20 minute intervals over 24 hours. This outcome is quite the underwhelming expectation for people who are trying to lose weight. By no means am I trying to deter people from high intensity interval training or even deter them from attending different classes based on a HIIT format. If this is something that you truly enjoy and are consistent with I’m all for it.
But, to proclaim that this is a superior method and protocol to become fitter above everything else for the purpose of selling a membership is sadly misleading. Selling the periphery of the group or class would be way more ethical. For example saying the group has an awesome energy and you will get a bunch of support from people who also have the same goals as you would be much more correct than to sell someone on half the picture of the actual science.
People that claim HIIT is the be all and end all answer for getting fitter, losing fat, and dropping weight are mistaken, and its a problem. Putting one type of exercise in opposition to another just makes it more difficult and confusing for people to simply start their health and fitness journey. And, at the end of the day it comes down to inspiring people into action and making sure more people are getting more active and healthy by proper information.
Not just to sell and close the next transaction.
References:
Børsheim, Elisabet and Bahr, Roald . “Effect of exercise intensity, duration and mode on post-exercise oxygen consumption.” Sports Medicine 33, no. 14(2003): 1037–1060.
Hazell, Tom J. , T. Dylan Olver, Craig D. Hamilton, and Peter W.R. Lemon. “Two minutes of sprint-interval exercise elicits 24-hr oxygen consumption similar to that of 30 min of continuous endurance exercise.” International Journal of Sport Nutrition and Exercise Metabolism 22, no. 4 (2012): 276–283.
Skelly, Lauren E. Patricia C. Andrews, Jenna B. Gillen, Brian J. Martin, Michael E. Percival, and Martin J. Gibala. “High-intensity interval exercise induces 24-h energy expenditure similar to traditional endurance exercise despite reduced time commitment.” Applied Physiology, Nutrition, and Metabolism 39, no. 7(2014): 1–4.
Williams, Cameron B. Jason G.E. Zelt, Laura N. Castellani, Jonathan P. Little, Mary E. Jung, David C. Wright, Michael E. Tschakovsky, and Brendon J. Gurd. “Changes in mechanisms proposed to mediate fat loss following an acute bout of high-intensity interval and endurance exercise.” Applied Physiology, Nutrition, and Metabolism 38, no. 12(2013): 1–9.
