How do we know how many calories are burnt?

Question

For example one burns about 200 calories while taking a walk.
Who figured that out and how?

In: 8

Answer 1

We can do indirect calorimetry. One liter of oxygen consumed equals 5 kcal (how that was determined, I don’t know). So we can do experiments to measure how many calories are used, such as having someone walk on a treadmill using a mask connected to a metabolic cart that measures how much oxygen they are using, then convert that to calories.

This process is used often in measuring efficiency and economy (for, say, a new type of athletic shoe or bike handlebar system).