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As you sit here and read this article your body is burning calories…lots of calories. Those calories are being used to keep your body alive and functioning, which we call your resting metabolic rate.
The efficiency of your metabolism may be one of the most important determinants of long-term weight loss success, but not in the way that you think…
Contrary to popular belief, we don’t want an efficient metabolism if our goal is fat loss; in fact, we want an inefficient metabolism. Let me explain…
Your adipose tissue (body fat) is like a gasoline tank. It can store immense amounts of energy which can be burned to keep your body alive and moving. If you have an efficient metabolism, your body essentially turns into a “Toyota Prius”, it becomes super-efficient and thus can go long distances while burning very little fuel. In essence, your body gets 100 miles per gallon and the car does not go very fast.
That is great if you’re at risk of starving to death, but not so great if your goal is to get lean…
If we trade the Prius in for a Ferrari, then you burn a lot more fuel traveling the same distance. In essence, your metabolism burns more energy to do the same things. That’s very good for weight loss purposes.
As we lose weight, there is often a discernable decrease in metabolism that means your body is running much more efficiently. Scientists believe that this decrease in metabolic activity is partially responsible for the weight regain experienced by many people after losing weight.
What We Learned From The Biggest Losers
The Biggest Loser was one of the most popular extreme weight loss shows to ever air. During the show, morbidly obese contestants would be shipped to live on a ranch where they would be fed a very low-calorie diet while doing ungodly amounts of physical activity.
The result…contestants lost HUGE amounts of weight during the course of a season.
Then the show would end, they’d go home, and most would regain every pound back…and then some.
Scientists wanted to find out why so few contestants managed to keep the weight off. They followed 14 contestants who lost an average of 58.3 kg (128 lbs) during the show and found that after losing the weight, their metabolisms dropped by an average of 610 calories per day. After 6 years, the drop in resting metabolic rate further decreased to an average of 704 calories per day despite regaining most of the weight. (Obesity, 2016)
There is a lot to learn from this study, however, the key takeaway for our topic is that weight loss generally results in a decrease in resting metabolic rate. In essence, losing weight, especially by using a calorie-focused approach (calorie-restriction and lots of aerobic activity) results in a much more efficient metabolism.
Due to the slowing metabolism, in order to maintain the weight loss, one would need to continue to decrease the caloric intake to near starvation levels. This approach of losing weight then cut more calories is just not a sustainable approach because the side effects of hunger, low satiety, lack of energy, increased stress hormones, and poor sleep would make it unsustainable.
An effective weight loss program should work to defend the resting metabolic rate and keep our metabolism burning inefficiently in order to innoculate ourselves against weight regain.
What Is EPOC (Metabolic Afterburn)
You will often hear personal trainers and health experts refer to EPOC, which stands for “Excess Post-Exercise Oxygen Consumption”. In essence, once you finish an exercise session, your body continues to burn calories at an accelerated rate for a period of time after the workout ends.
The engine of a car stays warm after the engine is turned off, similarly, your metabolism continues to burn after the workout is done. The hotter the engine gets, the longer the engine stays warm after it’s shut down. Likewise, the more intense the metabolism burns (i.e. the more intense the physical activity) the longer the metabolism will burn after the workout is over.
The theory is that by activating EPOC, you can counterbalance the slow, efficient metabolism induced by weight loss. The question is how many calories can you burn after a workout and is it significant enough to impact fat loss and potentially prevent weight regain?
How Many Calories Can You Burn From EPOC?
First, we need to understand an important distinction. EPOC speaks to the calories you burn, beyond your normal resting metabolic rate, as your metabolic engine cools down after an exercise session is complete. It is essentially a temporary increase in resting metabolic rate.
It’s important to note that EPOC is not the only influential factor in metabolism…
Your muscle mass plays an important role in resting metabolic rate, how many calories you burn during exercise, and EPOC. Thus the more muscle you have, the bigger your engine, and thus the hotter it burns.
It’s no secret that people who lose weight often lose muscle as they burn fat. This likely plays a big role in why the resting metabolic rate slows with weight loss, although research suggests that not all of the metabolic slowdown can be attributed to a loss of muscle mass. There are likely other hormonal causes to metabolic slowdown.
Now that we understand that muscle is important for keeping your resting metabolism burning bright, we should take steps to keep our muscles strong as we lose weight through resistance training and H.I.I.T, two exercise modalities that also lead to a boost in EPOC.
So how many calories can you expect to burn through EPOC?
The answer to this question is a bit complicated because certain types of exercise impact the intensity and duration of EPOC more than others. So, if you jog moderately on a treadmill for 30 minutes, the EPOC won’t be nearly as strong nor will it last as long as if you did 30 minutes of high-intensity interval training or 60 minutes of resistance training.
EPOC can last from a couple of hours, up to 36 hours depending on the type and intensity of exercise. In addition, EPOC starts off burning hot and decreases in intensity over time.
Although the research does not agree on what an “average” EPOC would be, most of the research we reviewed suggested that EPOC can amount to burning an additional 50-200 calories after the end of a H.I.I.T. or resistance training workout. That may not sound like much, but if you assume that this can be maintained day in and day out with a daily exercise plan, it can amount to 5 – 20 lbs of fat over the course of a year (not including the caloric deficit caused by the exercise itself).
Of course…that’s a theoretical benefit to prove that, all things being equal, 50-200 calories is significant.
What Causes Metabolic Afterburn (EPOC)?
The purpose of exercise is to stress the body for a short and intense period of time. This stress triggers a cascade of metabolic, chemical, and physiological events that work to restore homeostasis to the body.
Your body likes balance, exercise pushes the metabolism off balance, and after the workout is complete, a lot of stuff happens to restore the body to balance.
This process of rebalancing the body takes time and energy.
After intense exercise, the body gets to work:
- Restore glycogen stores – When you exercise, especially intensely, you burn away your precious sugar stores in your muscles and liver. The body doesn’t like this because you need this stored sugar to fuel an escape from a lion. So, energy is used to fill your muscles and liver with sugar.
- Restore oxygen to hemoglobin and myoglobin – At the end of your workout, your tissues are often depleted of oxygen as the heightened metabolism converts oxygen to CO2. So, your body burns energy in order to restore your oxygen debt.
- Metabolic hormones are heightened. Certain hormones and neurotransmitters flood the blood when you exercise intensely, these hormones keep the metabolism burning hot. It takes time for the effects of these hormones to rebalance. The lasting effects of these hormones impact the post-exercise burn.
- Muscle repair takes energy – After intense exercise, muscle is often damaged (in a good way) and the body gets to work rebuilding and repairing the muscle. While that repair happens, you will burn calories to fuel that repair process.
- Restore ATP – ATP is the energy source for life. When you work out, especially intensely, you deplete the tissues of ATP energy. As the body restores ATP, it burns energy.
How Does Exercise Intensity Impact Metabolic Afterburn?
All exercise has an afterburn, but the more intense the exercise session the more calories you will burn from EPOC and the longer that burn will last.
Exercise that increases your heart rate from 70 percent to 80 percent of your maximum heart rate will deliver the greatest EPOC effect and high-intensity interval training (HIIT) is one of the best ways to get your heart beating to this degree.
According to one study published in Applied Physiology Nutrition and Metabolism, cyclists and runners who performed an interval training session burned between 45 to 65 calories just within the first two hours following their workout.
According to a 2014 study by Mann et al, exercise intensity appears to be the most important factor in activating and sustaining EPOC. They tested male and female runners, having them run at 60%, 70%, and 80% of their VO2 Max. The results revealed that as the intensity increased the EPOC also increased. (Mann, et al., 2014)
If you choose to use high-intensity interval training, it is important to push yourself during the active phase. Aim for 80-85% of max heart rate during the active phase and 60% of max heart rate for the recovery.
What Is The BEST Form of Exercise for EPOC?
As we stated in the last section, the intensity is key for making the most of EPOC. There are three types of exercise that induce to best metabolic afterburn.
First, is high-intensity interval training in all its forms. It doesn’t matter much how you choose to do interval training, you just need to push yourself into the 80-85%+ of maximum heart rate. You can run, cycle, box, row, elyptical…it doesn’t matter what you choose as long as you work out hard.
Second is “Metabolic Resistance Training” such as Metabolic Renewal by Dr. Jade Teta and the folks at Metabolic Living. With metabolic resistance training, you are using large, multi-joint muscle groups along with short rest periods (30 seconds or less). By performing multi-joint resistance training you are burning ATP at very high levels, damaging muscle fibers, and increasing heart rate. Combining these exercises with short rest periods helps to trigger the hormonal event needed to trigger EPOC in a big way.
Finally, we have conventional resistance training. Conventional resistance training involves lifting heavy weights with longer rests between sets. The goal of conventional resistance training is not to trigger a metabolic hormone event like we do in metabolic resistance training, instead, it’s about building muscle and strength. When we lift heavy weights, we damage muscle. That damage muscle needs to be repaired and that takes energy, which leads to an EPOC effect. In fact, in one 2003 study by Bersheim and Bahr, heavy resistance training outperformed steady-state cardio and circuit training for it’s metabolic afterburn.
Of the three forms of exercise discussed, the EPOC is likely highest for metabolic resistance training, followed by high-intensity interval training, with traditional resistance training providing the least bump in metabolic afterburn.
Side note: These three forms of exercise are the most impactful for fat loss, partially because of EPOC, but for many other reasons that are beyond the scope of this article.
How Long Does The Metabolic Boost Last?
The research literature is not conclusive on this question, however, most research suggests that the afterburn can last from a few hours all the way up to 48 hours. Altogether, for most high-intensity exercise, it’s safe to assume a metabolic bump for 24-36 hours after the completion of the exercise session. This is important to note because it means you don’t have to do H.I.I.T. and metabolic resistance training every day, in fact, doing so could lead to overtraining due to the metabolic stress these types of exercise load on the body. It’s best to stick to three days a week of metabolic exercise while conventional resistance training and restorative activities like walking and light cardio can be performed daily.