It's much talked about, and it's alleged that many extra calories are burned. But is it real? If so, how can we get it? And is it even worth it?
The exercise afterburn effect is a phenomenon that occurs after completing a workout or physical activity. It is an ongoing elevated rate of calorie expenditure that may continue for hours or even days after exercise. This phenomenon is more scientifically known as Excess Post-exercise Oxygen Consumption (EPOC). The afterburn effect has been studied extensively and found to be both significant and beneficial for individuals seeking to lose weight or increase their overall fitness level. In short, when an individual engages in physical activity, the body uses up its reserves to fuel the workout. Therefore, after the exercise session, the body must replenish these reserves. As a result, recovery requires the body to burn more calories than if the activity had not been undertaken. This extra calorie expenditure is called the afterburn effect.
The body needs extra oxygen to replace the ATP (the front line of energy supply) and muscle glycogen used during the workout to recover to its normal resting state. It also restores the blood oxygen level and (somewhat counter-intuitively) has to work to lower body temperature. Oxygen/energy is required to mobilise protein to repair the damaged muscle tissues. The more oxygen is needed to restore the body to homeostasis, the more calories will be burnt post-workout.
The afterburn effect is generally considered to last anywhere from 15 minutes to 48 hours, depending on the intensity of the activity. High intensity interval training (HIIT) has been found to have the most significant afterburn effect, with some studies showing that the calories burned can be up to 15% greater than those burned during the activity itself. Studies do not tend to extend beyond 48 hours because the gains are small and hard to measure after that, but exceptionally, this study https://pubmed.ncbi.nlm.nih.gov/20886227/#article-details pursued results up to 72. It was reported that a one-set high-intensity resistance training session was shown to have the same effect as three sets in elevating resting energy expenditure in overweight college males tested. This effect was measurable all the way out to 72 hours.
The afterburn effect can be beneficial for those looking to lose weight, as it can help increase the number of calories burned throughout the day. It also helps to improve an individual's overall fitness level, as the body must work harder to replenish the energy stores that were used during the activity.
In addition to weight loss and increased fitness, the afterburn effect has also been found to have other health benefits. For example, it is believed to increase the production of testosterone and human growth hormone, which can help to build muscle mass and improve bone density. It can also help to reduce stress, enhance the quality of sleep, and reduce the risk of certain diseases.
Although the effect may be exciting, afterburn should not be confused with the thermic effect of increased muscle mass. Individuals with more lean muscle do burn more calories, even at rest, than less muscular folk. Whereas people who regularly train steady state cardio or endurance workouts may even burn fewer calories at rest because their bodies have been honed to greater heights of metabolic efficiency! The afterburn effect refers to the calorific cost of replenishing the oxygen debt of exercise, not the calorie burn of muscle mass or other normal resting physiological functions.
This study https://pubmed.ncbi.nlm.nih.gov/17101527/#article-details found the additional post-exercise calories to be in the region of 6-15% of the calories used by their subjects in the actual workout. They commented that the EPOC effect appears to increase linearly with the intensity of the exercise. In the aerobic workout zone, 60-65% of HRmax, we expect that the afterburn effect accounts for 0-5% of the calories used in the actual exercise. For more strenuous workouts, 75-85% of HRmax increases to 5-10%. High intensity training, whether resistance, interval or endurance, boosts that figure to 10-15% of workout calories!
There are no disadvantages to burning a few extra calories over and above what we set out to do in the gym or on the trail, but keeping the value of afterburn in perspective is essential. A 500kcal workout is going to result in an extra 75kcals burnt post-exercise. In this sense, optimism that EPOC plays an important role in weight loss is unfounded, especially since, as detailed above, achieving even that 15% figure requires a level of training intensity that is unlikely to be tolerable to a less athletic individual! However, every little helps; all calorific deficits result in weight loss to a lesser or greater extent, and reduction of excess weight has been shown to contribute to the quality of life as well as a marked decrease in all-cause mortality.
However, the duration and magnitude of the EPOC generated by high-intensity resistance training suggest that it would be a valid strategy as part of a weight management program for individuals who would commonly have opted for low-intensity, steady-state activity.
"A 15–20 minute HIIT session elevates your VO2max – which enhances aerobic endurance fitness – the same amount as 60 minutes of actual endurance training whilst torching a similar amount of calories" (Helgerud et al. 2007; Little et al. 2009; Tabata et al. 1996).
# Use a heart rate monitor with a suitable app to measure your exercise calories. Chest strap monitors are much more reliable than wrist devices.
# Make sure you enter your correct age and weight in the app. Otherwise, the results will be wrong.
# The harder you push yourself, the more bonus calories you'll use up. But don't get so obsessed with calorie burn that you train too hard or too long and cannot face it tomorrow!
# Rest/recovery and sleep are vital for the repair processes that use extra calories. Don't burn the candle at both ends!
# Use a calorie counting app to track your nutrition. There is little point in knowing what you burn if you don't know how much you're eating.
# Don't try to lose more than 1-2 lbs a week. You will have no energy, and your weight will bounce back up later. You might also be exposing yourself to health risks that are more severe than those associated with weight.
# Remember, the only exercise program that works is the one you can stick to! So count the calories, do the maths, but don't be so focussed on that last 100kcals that you stop having fun!
The afterburn effect is a beneficial phenomenon that can help individuals lose weight, increase their fitness levels, and improve their overall health. However, it is essential to note that the maximum afterburn can only be achieved with medium to high-intensity exercise and will not occur with low-intensity activities. Therefore, engaging in HIIT or other high-intensity activities is recommended for those hoping to take advantage of the afterburn effect. However, always seek professional medical advice before embarking on such a program.
Check back soon for a rant about why you don't know your BMR or how many calories you're actually digesting. In the meantime, don't forget to breathe!
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