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This Is How Many Calories You're Actually Burning When You Work Out

Because the treadmill lies.

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1. First, you should know that the number you see on the treadmill and other gym equipment is probably wildly inaccurate.

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"Usually exercise equipment – like ellipticals and stair climbers – isn't the best thing to go off of [when it comes to judging calorie burn]," Luke Corey, a registered dietician and sports nutritionist for high level athletes with EXOS Performance Training, tells BuzzFeed Life. "[Machines] only require you to enter your age, height, and weight and then compare it to the average. The calories you burn is extremely specific to your body, which is why we don't even look at those numbers here with our athletes." Research backs this up.

2. And that's because the calories you burn depend on a lot of factors that the machines at the gym can't track.

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A lot more goes into determining how many calories your workouts burn than just your age, weight, and gender.

"There are so many factors that go into how many calories you burn that the gym machines don't consider, such as the level of intensity you're working out at, your body temperature, your workout environment (temperature, wind, rain), your muscle mass, your resting metabolic rate, your fitness level, and they're also horrible at tracking your heart rate." says Heather Milton, M.S., C.S.C.S., exercise physiologist at the Sports Performance Center at NYU Langone Medical Center. "The fitness trackers at the gym aren't individualized enough and that's why they're usually so far off in their estimates."

Your daily diet, sleep habits, body-fat percentage, and general metabolism also come into play. Here's a lot more information on that, if you're curious.

3. Let's go over how your body burns calories. It's actually all about oxygen consumption.

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You’ve probably noticed that when you are pushing yourself hard in a workout your heartbeat increases and your breathing gets short and rapid. This happens because your heart is trying to get as much oxygen as it can and pump it out to your muscles so they can produce ATP [adenosine triphosphate] energy, which is what fuels your body during the workout.

Now, for every one liter of oxygen you breathe in, you burn five calories. So people who huff and puff more during their workouts will be burning more calories than people who don't breathe as heavily. This means that a workout will be more taxing — and will therefore burn more calories — for someone who is in worse shape.

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4. There's an equation you can use to get a general sense of how many calories you burn during a workout.

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"Bear in mind this is another imperfect estimate based on lack of consideration of fitness level, age and gender," Milton says. "But it does get you a pretty accurate number of how many calories you're burning." Here it is.

Don't worry, it's a lot simpler than it seems. We'll break it down for you:

Let's say a 150 pound woman went on a 30 minute run at a 5 miles per hour pace (12 min/mile) and wanted to know how many calories she burned.

1. First you have to figure out the intensity rate at which you're working out, also known as your metabolic equivalent or MET. Your MET number can range from 0.9 (when you're asleep) to 23 (running at a 4:17 mile pace.) Here you can find a list of activities and the metabolic equivalent to go along with it. In this case, for a woman running at 5 miles per hour, her MET would be 8.3.

2. Then you need to multiply the MET number by 3.5 because you consume 3.5 milliliters of oxygen per kilogram of body weight. So it would be 8.3x3.5 = 29.05.

3. Once you've found that number, multiply it by your weight in kilograms (if you're converting from pounds divide your weight by 2.2046.) So 150/2.2046 = 68.04 kgs. Then 68.04x29.05 = 1,976.562.

4. Next, you take that number and divide it by 1,000 to get the number in liters. 1,976.562/1,000 = 1.976562.

5. Then multiply the number you got by 5, because as we said earlier, for every 1 liter of oxygen breathed in that's 5 calories burned. 1.976562x5 = 9.88281

6. And finally take that number and multiply it by the amount of minutes you worked out for, and that is the number of calories you ~burned~. 9.88281x30 = 296.4843.

Therefore, the 150-lb woman jogging at 5 miles per hour for 30 minutes would have burned around 296 calories during that workout.

5. But if math isn't really your thing, there are apps and wearables that will do the work for you.

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"As long as an app or wearable takes into consideration your heart rate, the duration of your exercise, the type of exercise, and your weight, age, gender, and fitness level, it should be able to give you a good estimate," Milton says.

She recommends MyFitnessPal for getting an estimate of calories burned during specific exercises, but says to keep in mind the number is only based on the duration you exercised for, the type of exercise, and your weight. She also suggests the calorie burning calculator on Health Status because it considers height, weight, gender and age, and Why I Exercise, which uses METS to estimate the different calorie burns for different exercises at different weights (basically what the calculation above does.)

Other apps you can try are the Nike + Running app which you can sync with a heart rate monitor, and the Azumio Instant Heart Rate, which will detect your pulse and tell you how hard you're working.

6. The wearables that accurately track your heart rate are going to be the best at estimating the calories you've burned.

"If your goal is to be more mindful of being more active, than any of the fit technologies and websites will be useful," Milton says. "But if you're talking about accuracy of the device in telling you something specific about your workout such as heart rate or how far you've run, then that's going to determine the wearable you wear."

If you're trying to record calories burned for specific endurance exercises, like running or cycling, you need to accurately track your heart rate, and the best way to do that is with a chest heart rate sensor. Corey and Milton recommend the Polar H7 heart rate sensor, which has an adjustable strap and can be worn comfortably under your clothes.

Some other great options are Jawbone wearables for tracking heart rate, Garmin watches for tracking distance (because of the GPS), and Fitbit wristbands, which track heart rate as well as other areas of health that improve your quality of life.

Heads up, though: Trackers won't be as accurate if you're working out smaller muscle groups — like if you're doing bicep curls, for example. That's because the blood volume you're using is going to go up and your heart rate will go up, but it won't be burning as many calories because it's not a total-body expenditure, like running is.

7. Knowing the number of calories you're burning in a workout can help you better understand or improve other aspects of your health and fitness.

8. But in reality, calories are definitely not the be all end all. There are other awesome ways you can track your fitness progress that don't involve calories at all.

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"The take home is that so much goes into your calorie burn and weight loss that dwelling on specific calories is never a good idea because it can cause stress and frustration when the calories in: calories out math doesn't lead to the desired pound loss or gain on the scale," Milton says. "Choosing a specific, reasonable and obtainable performance goal to track can be much more beneficial for improving outcomes, health, and quality of life."

Basically, if you're trying to lose weight, it's not as simple as cutting 3,500 calories and losing one pound. Instead, Corey recommends a lot of 'self monitoring'. "If you're gasping for breath and you feel like your workout intensity is an 8 on a 1 to 10 scale, then you're probably burning a lot of calories," he says. "Try to focus on the progress you're making, whether it's if you're running longer or lifting heavier. That will be a good indication of how hard you're working."

Instead of focusing on the amount of calories you're burning, you can try setting goals for yourself and measuring your progress that way, whether it's improving your 5K time, trying to stick to a specific workout schedule, lifting progressively heavier weights, or just enjoying the way your clothes fit or how healthy you feel.