How are calories burned by exercise determined?
A calorie is a measure of energy. Even at rest, the body requires a certain amount of energy to stay alive. Exercise raises that requirement. To test how much energy expenditure a given exercise will require per minute, say, can be done in several ways. One way is to get a lot of people to exercise under very particular circumstances over the course of a few months and monitor their weight, then do the math. How much metabolic energy is stored in a given mass of body fat is a known quantity, so determining how much of it was used, plus energy from food, minus baseline energy requirement, divided by the time spent exercising, determines the rate of calorie burn of that level of exercise. I say “a lot of people” because you’re going to want an average value from as large a sample size as possible, so that incidental factors will tend to cancel out. None of the numbers you see for this sort of thing will be exact. They’re all approximate. Even the amount of calories in the food you eat is
