Many people will agree that diet and exercise are the foundations of successful fat loss.
That means to reach a body composition goal, you’ll have to change the number of calories you eat or the amount/type of exercise you perform. But how important is exercise for burning calories and is it possible to reach your weight loss goals without it?
In reality, the most important factor for changing your body composition is your nutrition. In other words, how many calories you eat is more important than how many calories you burn. That’s because the time you spend exercising (burning calories) represents only a small piece of your total energy expenditure (TEE) on a given day. That’s not to say that exercise isn’t important for fat loss—it plays a role in overall calorie balance. But the number of calories you burn during exercise is dependent on lots of variables, and most gym equipment, trainers, and exercise systems will grossly overestimate calorie expenditure in an attempt to oversell their product. Fortunately, science can help us determine the real calorie expenditure from exercise. With the truth about energy burn, we can get a better handle on how our exercise (and nutrition!) will work with us on a journey toward our better selves.
So, let’s jump into the meat of it: How do we determine calorie expenditure, how does it affect our TEE throughout the day, and how important is all this for achieving our goals?
The Important Factors For Burning Calories
As mentioned, there are several factors that influence energy burn, including intensity, duration, and the type of exercise. The frequency of exercise also becomes a key factor in deciding energy expenditure over several sessions.
Intensity refers to the amount of effort used while exercising. Essentially, the intensity of the exercise will determine the rate at which calories are burned. More intense types of exercise burn more calories per unit of time than less intense types of exercise—and that probably doesn’t blow your mind. For example, brisk walking is considered moderate intensity, jogging is vigorous intensity, and sprinting is high intensity . However, it’s important to know that intensity is also relative to your capability. A brisk walk could be easy, moderate, or hard, depending on who’s walking. This is one reason why exercise equipment isn’t very accurate: it doesn’t take the exerciser’s fitness (or lack of fitness) into account. Usually, this means they overestimate calorie burn!
The duration and intensity of exercise work together to determine calorie burn. The number of minutes that you exercise (duration) is multiplied by the rate of energy use (intensity) to estimate a total calorie expenditure for the exercise . When it comes to body composition changes, this is incredibly important, because even though a given exercise bout may feel extremely hard, you still need to spend enough time doing it to burn a lot of calories. For instance, one full-out 200-meter sprint is going to feel much harder than jogging 1,000 meters. But the calorie expenditure is likely much greater for the jog compared to the sprint, because the jog took longer.
When it comes to frequency of training we have to think about the effect our training session has on the week as a whole. When durations are equal, there’s no doubt that higher intensity exercise burns more calories. However, that intensity comes at a price, because it’s a lot harder to recover from high-intensity exercise. A crushing interval workout might leave you sore and exhausted for several days, and research shows that athletes and non-athletes alike typically require at least three days to fully recover from these sessions [6,11]. If you wait until you’re fully recovered, you’d only manage two sessions (at best) each week. While a less intense session may burn fewer calories, you’ll be able to exercise more frequently which could lead to greater calorie burn in the long run.
Heavy Weights for a Heavier Burn?
The popularity of resistance training (lifting weights) is on the rise, and so is the focus we give it for burning calories. The metabolic demands of picking things up and putting them down again are much different compared to aerobic exercises, like running. While resistance training doesn’t burn as many calories as aerobics do, some claim that the benefit of lifting weights comes later—after the session is over. Because your body is burning extra calories while recovering from training in the gym (a fancy bodily feature called Excess Post-Exercise Oxygen Consumption, or EPOC) proponents will argue that lifting weights has a big effect on TEE. But does resistance training really burn as many calories as people claim?
One study found that a typical bodybuilding-style workout using three sets of nine exercises with 90 seconds of rest burned around 230 calories . They also found that the subjects burned about another 25 calories from EPOC after training was completed. These results are fairly typical for how many calories are burned during heavy resistance training and the EPOC period that follows. Interestingly, circuit-style training burns more calories compared to heavy resistance training, although the difference between the two isn’t considered significant . The reason for the slight bump in calorie expenditure is likely due to the shorter (or non-existent) rest periods in traditional circuit training. However, the EPOC from heavy resistance training is significantly greater than that of circuit training , so it balances out.
While it’s clear that 25 calories of EPOC seems not that significant, we also have to examine the effect that resistance training has on metabolism outside of that initial two hours. Resting metabolism tends to remain elevated for up to 21 hours after heavy resistance training . Also, the increase in muscle mass from lifting weights has a positive effect on overall metabolism. In fact, TEE can be elevated by about 180 calories per day as a result of gaining four pounds of muscle . These small bumps in metabolism can make a meaningful change when it comes to overall calorie burn.
Cardio and Burning Calories
In most forms of cardio—like sprinting, jogging, swimming, biking—you’re going to be moving your own body around, a lot. That’s a little different from resistance training, which (by definition) involves a resistance from the outside, like a dumbbell. Because it’s your body against the clock, the amount of energy you burn along the way depends greatly on your fitness level, efficiency, and body mass. Two people jogging at 5 miles per hour are likely going to burn different amounts of energy. But even the differences in how each exercise mode is performed will change the calorie expenditure. This makes relying on calorie estimates from cardio a tricky business.
One study investigated the difference between running and walking a mile on both the treadmill and on the track. They showed that running a mile (at 6.3 mph) burned about 115 calories compared to just 80 calories from walking the same distance . Obviously running is more intense than walking, which explains some of the difference in calories burned. But factors like the amount of movement, stride length, stride frequency, and aerodynamics are just a few factors that also contribute to the discrepancy. Cycling can burn anywhere from 50-75 calories per mile depending on riding speed, pedal rate, combined body/bike weight, etc. That means that if you rode 10 miles, you could burn 500 calories or 750! That’s a big difference, and it makes it hard to rely on calculators or equations to predict calorie expenditure from exercise.
What we can rely on is the old intensity and duration rule. In terms of cardiovascular exercise, we might compare something like high-intensity interval training (HIIT) to low-intensity steady state (LISS) exercise. While sprinting burns a lot of calories, you often spend less time doing it compared to going for a jog. However, when you look at TEE, it turns out that HIIT causes a similar increase compared to LISS, despite burning fewer calories during the actual session . That’s because sprinting has a robust effect on EPOC.
Research shows that intensity is the most important factor that contributes to the EPOC from exercise .
One benefit of highly intense exercise is that you get more calorie burn with less time invested. But remember that highly intense exercise may keep you down and out for several days while you recover. Two bouts of steady state exercise are better than one bout of HIIT in this case. So, you have to pick your battles when it comes to cardio.
The Reality of Energy Burn
While exercise is an important part of the energy balance equation, remember that it’s only a tool. Although it may add several hundred calories to our TEE, we will still burn thousands of more calories throughout the day from general activity, organ functions, and even sleep!
Also, because it’s so hard to accurately guess the calorie expenditure from exercise, it’s not a good idea to assume you’ve burned a certain number of “extra” calories from working out. The best way to ensure fat loss is to control your macros and calories, and make sure that number is smaller than your calorie expenditure for the day. But whatever exercise you choose for your journey, remember that you have to push yourself in order to get results. New exercise styles that boast huge calorie burns with less effort are always too good to be true. Don’t seek out gimmicks and the hot new trends. In the end, a well-controlled diet with a fair amount of exercise will result in long-lasting changes to your body composition and health.