Why Do Treadmill Calorie Counters Vary with Speed?

[pushkarvaidya]

I have a very basic question related to energy here.
We all know that calorie is a measure of energy.
Also Energy spent = work done (ignore efficiency)

When you walk 1 mile on a treadmill you are doing some amount of work. Based on the above equation you are using up some amount of energy. This energy is measured in calories.
Now suppose you walk the same distance, but in half the time, you are still doing the same amount of work (of walking 1 mile) so you are using the same amount of energy. The only difference is that you are doing it at a faster rate.

Why does the calorie counter on a treadmill give dramatically different values in both of the above cases.
Is the work done in both cases not the same? Should the calories burned not be the same?.

Please help me resolve this question.

 

[FredGarvin]

Mechanical work is not the same as the chemical work your body has to do. While you are still going the same distance, think of how many more times during that mile that you breathe and your heart beats. Think of how much warmer your body becomes. All of that is the extra work you are not accounting for by simply looking at the mechanical work.