# Calories Burned on Apps

How do they come up with the calories burned figure on exercise apps. Th elliptical machine at the gym says 400 in 30 minutes. One biking app says 1000+ for a 20 mile bike ride in 1 hour 20 minutes. A different app says 550 for the same ride. I’m not counting calories, just curious about the method they use to calculate.

I’ve seen legit exercise studies that show on how many calories are burned under different cricumstances. I know how they measure it; however, these are estimates at best and depend greatly on the conditions, your fitness level, etc. For example, I do a lot of hiking and have seen apps that give me 100 to 200 calories burned for every mile I hike. The app knows my speed and elevation changes, but it’s still just an estimate. Whether I am burning 100 or 200 calories for every mile I hike doesn’t matter much to me, as long as I am burning calories!

it’s a technology called “WAG” or Wild-Assed Guess. If the tech is a bit more advanced, it uses things like asking for your weight, measuring activity (movement) with the sensors on the phone (or Apple watch) etc. All to better hone that guess.

But yes, my Bowflex C6 bike will tell me that I performed 375 calories of exercise, my Apple watch says 290, and the Peleton app on the iPad says 165. The bike is probably most accurate, since it is using electrical resistance to put a load on the pedals, monitors speed, and knows how much energy I actually need to turn the wheel.

The Apple watch can get my resting and active heart rate, to make a better estimate than just “guess”. The Peleton app only knows the pedal cadence, not the resistance setting, so is making a less refined estimate. (and I probably weigh more than their typical client).

I wonder if some apps are calculating how much mechanical work you’ve done and expressing that in calories, while other apps might be assuming a value of thermodynamic efficiency for the human body and calculating how many calories of food you need to take in to offset the mechanical work you’ve put out. The latter would be of more interest to people, because it would tell them how many energy bars they could eat without expecting to gain weight.

Most calorie-counting apps probably use a pre-determined metabolic equivalent of task value for the activity, and then a simple formula to factor in duration and your weight. That’s why the apps will have specific activities you can select, but also a custom workout that asks you to rate the intensity of the workout.

As a for-instance, this website uses:

Total calories burned = Duration (in minutes)*(MET * 3.5 * weight in kg)/200

So an elliptical at the gym probably (WAG here on my part) determines your calories burned as an ongoing recalculation of your MET based on your speed/resistance/elevation, as well as other provided data (a lot of them let you enter your age and weight, and have ways to track your heart rate). Or possibly it doesn’t measure anything and just has pre-determined values based on a single setting.

But it’s never going to be more than a very broad estimate.

In a lab, they can measure it by hooking up hoses to an athlete’s face, and measuring the amount of oxygen they’re consuming. The metabolic processes are fixed and known, so given the amount of oxygen, you can determine the number of Calories. Presumably, they do this for a whole bunch of test subjects of different heights, weights, genders, etc., so they can interpolate what any given person will burn.