More Than 3x Higher EPOC Induced Energy Expenditure With HIIT vs. LISS! But Does That Really Matter? Plus: Why Headlines Like This May Compromise Your Progress

If you are sprinting because of the increase in EPOC, you are a fool.
Those of you have been following the SuppVersity for quite some time, now, will be familiar with the term "EPOC", which refers to the amount of oxygen that is consumed in excess in the post-exercise - or, in order not to overcomplicate things, the excess post-exercise oxygen consumption, or, even simpler the amount of energy your burn after a workout because your mitochondria are "still on fire".

Assuming that you have read those of the >1250 hitherto published SuppVersity Articles that were dealing with this issue you may remember that I have repeatedly pointed out that...

... the contribution of the actual energy consumption that is caused by the "EPOC effect" would be absolutely irrelevant, if the calories in vs. calories out equation was as simple as mainstream dietitians and lifestyle magazine authors still like to present it to their clients and readers.

Now you know better than that so that I don't have to tell you why I do even care about the results of a recent study from the Universities of Central & West Florida (Townsend. 2013). After all, the EPOC is by far not the only metabolic effect that's missing from the "standard equation of exercise-induced weight loss", i.e. [calorie intake - (resting metabolic rate + calories burnt during exercise)] / [3,500 kcal/lbs] = amount of fat lost (in lbs).

Let's get to the study first!

HIIT does not work because it burns more energy! As Williams et al. (2013) observed recently the benefits of HIIT don't come from...,
  • an increase in EPOC (excess post-exercise oxygen consumption)
  • an increase in resting energy expenditure (RER), which actually drops in the 60min after exercise, and
  • a larger amount of fat being burned during the workout
So if it's none of these, does HIIT work at all? Well if you asked Williams et al. they would probably say that based on their results it works because of its appetite suppressive effects, which have by the way been demonstrated by in another recent study that is about to be published in the scientific journal Obesity (Sim. 2013).
What is yet of much greater importance is that HIIT is intense enough to actually enforce adaptation and mitochondrial biogenesis. It helps you to build a bigger engine and the latter will help you in your efforts to lose weight and build muscle.
Before we get into the discussion, whether or not the 200% increase in EPOC Jeremy R. Townsend and his colleagues observed in 6 recreationally-trained males (age: 23.3±1.4 yrs; body mass: 81.8±9.9 kg;  height:180.8±6.3 cm), let's first take a look at the different exercise protocols the participants were exposed to on the two testing trials that were scheduled to take place at the same time of the day to minimize the effect of the circadian rhythm.
  • a moderate aerobic exercise protocol consisting of a 30-minute submaximal cycling bout at 60% of heart rate reserve on an electronically braked cycle ergometer (HRR), and 
  • three repeated 30-second Wingate cycling tests separated by four minutes each on a Monark 894E cycle ergometer (SIE).
Three hours before each of the trials, the subjects consumed a standardized meal replacement bar (43 g carbohydrate, 10 g protein, 6 g protein, 1004.6 kJ total). Water was consumed ad libitum and each testing trial was separated by 48 hours and was implemented in the random counterbalanced design.
"Recorded data in SIE consisted of peak power output, mean power, and fatigue index. [...] Following testing trials, supine VO 2 was measured for 30 minutes or until baseline measures were reached. A participant was considered to have reached baseline when the average of two consecutive minutes was equal to baseline values.

EPOC was determined by subtracting baseline VO2 from post-exercise recovery VO 2 measurements. [...] Energy expenditure (kJ) was determined by multiplying kcals per liter of oxygen (20.93 kJ∙L O2) by the average VO 2 during recovery." (Townsend. 2013)
As the data in figure1 goes to show you, both the VO2 and EPOC values were significantly higher during the 30 minutes of post-workout recovery in the SPIE group.
Figure 1: EPOC and corresponding additional energy expenditure in the high intensity 3x Wingate group (SPIE) and the 30min continuous exercise group (HIE) during the 30 min right after the workout (Townsend. 2013)
In fact, the average EPOC value was 316% higher in the SPIE group. This value is, however, deceiving as it does not reflect the actual difference in post-workout energy expenditure which was 39.75kcal vs. 10.25kcal and thus "only" 287% higher in the SPIEE group.

"Hold on, you mean 397.5kcal, right" NO, I don't! It is, in fact, nothing but a fifth of an apple and you don't want to tell me that this will make a difference, right?

If you are training like Haile you better are a marathon runner. If you do that to lose weight or have reached the point, where you need to do it not to gain weight, it's time to make a change, because in that case, the cardio is already hampering your gains and progress towards the physique you are aspiring (learn more). Train to build a bigger engine and eat to support your muscle gain or fat loss goals, not vice versa!
Thus we are back to the initial question whether EPOC matters... now if you look at the figures, you will have to admit: It does not matter. But guess what, the same is true for the 600kcal you may be spending doing LISS everyday.

If you are still heading to the gym to "burn calories" you really don't deserve the physique you're torturing yourself for. Train to get healthy, train to stay healthy, and train to build a bigger engine (which requires progressive, intense training on the track and in the gym) and have your diet take care of the rest.

Does this mean there is no role for cardio exercise in your regimen? No, it does not, but once you have achieved a point, where you are just performing it to "allow yourself that additional sweet potato", it's about time to make a switch... unless the physique you are aspiring is that of Haile Gebrselassie.

So what can you do? Lift weights, improve your conditioning and diet, if you feel you have got to lose weight, but don't train to lose weight. Train to maintain weight: Muscle weight! Train to get faster, train to get stronger and train to build your endurance. Record your progress set short-term goals for the gym, the track, and the kitchen, be patient and cherish every success and you will shed that belly, not despite, but because you are not "burning enough calories".

  • Sim AY, Wallman KE, Fairchild TJ, Guelfi KJ. High-intensity intermittent exercise attenuates ad-libitum energy intake. International Journal of Obesity advances online publication 9 July 2013. [epub ahead of print]
  • Townsend JR, Stout JR, Morton AB, Jajtner AR, Gonzalez AM, Wells AJ, Mangine GT, McCormack, WP Emerson NS, Robinson EH, Hoffman JR, Fragala MS Cosio-Lima L. Excess Post-Exercise Oxygen Consumption (EPOC) Following Multiple Effort Sprint And Moderate Aerobic Exercise. Kinesiology. 2013; 45(1):16-21
  • Williams CB, Zelt JGE, Castellani LN, Little JP, Jung ME, Wright DC, Tschakovsky ME, Gurd BJ. Changes in mechanisms proposed to mediate fat loss following an acute bout of high intensity interval and endurance exercise. Applied Physiology, Nutrition, and Metabolism. 11 June 2013 [epub ahead of print]
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