# How many calories did I really burn on that run?

It’s pretty common for exercise apps, running machines, etc. to quote a number of calories burned during a work out. How are these numbers calculated?

The amount of “useful” work done should be pretty easy to estimate, i.e. you’ve moved a Akg body at Bm/s for Cs, so you’ve done X calories of work.

But as the human body is machine, and its not 100% efficient, you have actually burned far more than X calories, you have burned eX calories where e is the efficiency of your body, as a machine for converting chemical energy into kinetic energy. e seems much harder to estimate sensibly. and seems like it will vary greatly between people (I am sure an Olympic athlete would barely break a sweat on a work out that would half kill me).

Is there a some agreed upon estimated value for e everyone uses to give you a “calories burned” number? Do they just assume a value of 1.0 (i.e. your body is perfectly efficient)? Or are there more complicated formula that take into account weight, age, height, heart rate, etc?

Here’s a chart from the Mayo Clinic - http://www.mayoclinic.org/healthy-living/weight-loss/in-depth/exercise/art-20050999?pg=2

Your bodyweight is probably the biggest variable in the equation. I’m sure age and body composition also factor in but my uneducated guess is that they’re relatively minor. The references to that chart may have more detailed methodology.

Thanks. Its not exactly what I was after. but sounds like MET is as close as I am going to get. Don’t exactly see how that maps to mechanical efficency, but I think it must to some degree.

The other issue, as explained by **DSeid **here http://boards.straightdope.com/sdmb/showpost.php?p=18054392&postcount=15 is that those estimates are usually what you burned. Not what you burned in excess of what you would have burned sitting in a chair breathing & keeping your body alive but idling.

And only that excess represents progress towards a goal of weight loss. Not everybody exercises for the purpose of weight loss, but folks interested in calories usually are.

The MET values I mention above do take that into account (basically MET of 1.0 is basically defined as what an average adult would use sitting on the couch)

That’s why it seems like an mechanical efficiency value is useful. If you are actually interested in getting from A to B then you want to be efficient. You want as much energy as possible expended doing useful work (as in converted to kinetic energy). If you are just interested in losing weight you want to as inefficient as possible (as you don’t care if the energy is “useful” or not you just want to “use it up”).

Inefficient exercise may not be enjoyable, and you’ll do less of it. If I’m out for a bike ride I’d rather be on an efficient, well tuned bike so I can cover more ground and see more things. That makes my ride more enjoyable and I’m more likely to keep going.