how to determine how many calories an activity burns?

[dreamache]

I know there are tons of sites out there that show you how many calories an exercise will burn depending on your weight, age, intensity and how long the activity was performed...

but how exactly do they arrive at these numbers, if anyone knows the equations and such i'd appreciate it! thanks!

[paul1454]

Well it has to do with the amount of work required to do certain activities. Work is simply Force x distance. So all you really have to do if figure out about how much force, in Newtons, something takes to perform then multiply by distance (distance is probably an average because people are different heights, so with longer legs arms distance would be greater). Then they average how many times you would produce that amount of work if you were to do that activity for an hour (because it is usually measured per hour). Work is measured in Joules just as energy is. Calories are units of energy. I can't remember the conversion right off the top of my head, but I'm sure that wouldn't be terribly hard to find on the internet. Then they convert from Joules/hour to calories/hour. If this is confusing, sorry. It is really a lot of information that is required to get to those numbers, but I tried to simplify it as much as I could.