September 27, 2023 by Fuel & Fortify
Burning Questions: What You Need to Know About EPOC
Intense workouts have a remarkable way of making us feel weightless, almost as if we’re floating on a cloud. This sensation is not just due to the rush of endorphins that flood our system during and after the workout—it’s also the result of a fascinating physiological process that unfolds as our bodies return to their baseline state, recuperating from the beneficial stress we’ve subjected them to.
Numerous studies have shown that our bodies continue to burn more oxygen and calories during the post-exercise recovery phase compared to before the workout. This heightened metabolic activity occurs as the body resets, restores, and adapts in response to the training load. We’ll delve deeper into the energy expenditure that causes all this shortly, but one thing is clear: intense exercise jolts your metabolic rate, and it doesn’t immediately return to its resting state once you’ve completed your workout. Instead, it remains elevated for a brief period, keeping you torching (some) calories for several hours afterward.
This post-exercise calorie-burning phenomenon is commonly known as the “afterburn effect” or Excess Post-Exercise Oxygen Consumption (EPOC). Now, when we consider the trio of triathlon sports—swimming, cycling, and running—and control for intensity and duration, the question arises: is there a preferred mode to maximise EPOC and post-exercise metabolism?
This exploration in this post is prompted by various claims, like the assertion that swimming has a superior impact on metabolism compared to other forms of exercise. It’s essential to approach such claims with caution, as they often oversimplify the intricate network of factors influencing metabolic responses to various activities.
Metabolism Is Complex
Metabolism refers to the complex set of chemical processes that occur within the body to maintain life. It includes various components, such as the resting metabolic rate (RMR), thermic effect of food (TEF), and the thermic effect of activity (TEA). Exercise affects TEA, which represents the energy expended during physical activity. However, it’s just one component of metabolism.
EPOC is not the same as metabolism—rather, it’s a metabolic process within the body. Specifically, it’s a component of this TEA response.
What is EPOC?
EPOC refers to the increased rate of oxygen intake and calorie expenditure that occurs after a bout of exercise. Essentially, EPOC represents the energy your body expends to return to its pre-exercise state, including replenishing energy stores, repairing tissues, and eliminating waste products generated during exercise.
So in simple terms, EPOC can be defined as the amount of oxygen the body needs to recover after a training session. When we call a wrap on a session, your body doesn’t immediately return to its resting baseline. Both your heart rate and respiration rate remain somewhat elevated because your muscles still demand and use more oxygen even after the exercise has finished. This additional consumption of oxygen to get you back to baseline is what we refer to as EPOC.
In 2014, Mann et al. conducted a study investigating the recovery rates of male and female runners following exercise at 60%, 70%, and 80% of their VO2 max. The findings demonstrated that the most intense workout, performed at 80% of VO2 max, resulted in the most pronounced afterburn effect, indicating that EPOC was positively correlated with exercise intensity.
Regarding the duration of these effects, it’s worth noting that there’s a compelling upside to intensifying your workouts: there exists not just a linear, but an exponential relationship between exercise intensity and the overall magnitude of EPOC. In one study, EPOC values following an 80-minute workout at 75% of VO2 max were a staggering 23 times greater than those resulting from an effort performed at 29%.
Nonetheless, it’s important to maintain a sense of perspective and not become overly fixated on the EPOC factor. Traditional exercise physiology has long established that burning a liter of oxygen corresponds to approximately 5 calories expended. Applying this calculation to the previous example, we’re looking at an enhanced calorie burn of 150 calories–—equivalent to about the caloric content of 20 almonds. This context helps us appreciate the benefits without losing sight of the bigger picture—in that EPOC is nothing more than a marginal gain.
As a rule of thumb, EPOC comprises only 6-15% of the net total oxygen cost of the exercise. So if you burn 600 calories in the workout, EPOC will kick in a burn only about 36-90 calories.
Priortise HIIT
As we’ve already partially touched on, High-Intensity Interval Training (HIIT) and steady-state aerobic exercise have distinct impacts on EPOC. HIIT, characterized by short bursts of intense exercise followed by brief recovery periods, often leads to a higher EPOC effect compared to steady-state aerobic exercise.
What’s happening at a molecular level though?
ATP serves as the body’s primary energy currency, powering our body’s every movement. The generation of ATP occurs through either anaerobic processes, which don’t rely on oxygen, or aerobic processes, which involve oxygen. HIIT taps into our anaerobic energy production, such as sprint intervals, where instant energy is needed, albeit in a less sustainable manner. In contrast, endurance athletes rely on aerobic pathways to maintain prolonged exercise at a steady pace. So as exercise intensity increases, so does the accumulation of oxygen debt and the subsequent EPOC effect.
HIIT’s intense efforts create oxygen deficits in the body, and during the recovery phase, the body expends additional energy to restore homeostasis and repair muscle tissue. Additionally, an increase in lipid metabolism has also ben observed, which may benefit fat loss.
Swim, Bike, Run
If we circle back to the core of our investigation in this article: swimming, cycling, running—–does any one of them trigger a more notable uptick in EPOC compared to the others?
The short answer: not really.
This study found that EPOC was virtually equivalent between short intense bouts of cycling and uphill running. Despite differences in aerobic energy demands, when accounting for anaerobic energy expenditure, both forms of exercise resulted in comparable EPOC levels.
As for swimming, there is a notable absence in the research literature of a direct comparative study involving humans that measures EPOC values when comparing running/swimming and cycling/swimming (we stress “humans” here, considering that there is a bunch of literature exploring EPOC effects on various fish species—peculiar but it’s interesting stuff.)
In the context of swimming observed independently, the existing research further supports this linear correlation between oxygen uptake and exercise intensity (swimming speed in m/s3).
While there’s zero doubt that exercise intensity influences EPOC, it’s just a fraction of total calorie burn. HIIT provides the best bang for buck in more ways than one—but most certainly in relation to EPOC. While steady-state aerobic exercise has a milder effect. Yet, no single mode–—swimming, cycling, or running—clearly trumps the others in boosting EPOC.
Instead of obsessing over increasing EPOC, which has a relatively modest overall effect, consider it as an intriguing window into the intricate science of how the body’s metabolism reacts to various forms of exercise.
We hope we’ve done that for you here!