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In an ideal world, we’d be able to easily measure our [[Running Economy]] and see if things are improving. If we could measure our breath, find out how much O<sub>2</sub> we consumed and how much CO<sub>2</sub> we produce, we’d know how much energy we burned (and from fat or carbohydrate). Sadly, this is not practical, so the best measure we have of energy consumption is our
heart rate. This is far from perfect, as heart rate can vary for other reasons besides supplying O<sub>2</sub> for energy production. However, I believe it is a useful approximation.
=How to use the efficiency value=
The calculated efficiency value cannot easily be used to compare different runners. It can be used as to track how your running efficiency is improving over time. Over the weeks and months of training your efficiency value should gradually improve. For instance, I've seen my efficiency go from 110-120 to 130-150 over a period of a few months. Sadly, I've also seen my efficiency dropped when I put on body fat (see [[Weight Loss and Performance]].) This evaluation of my fitness this proved to be remarkably useful to me.
==Efficiency and Glycogen Depletion==
Another use for the efficiency value is to compare values within a run. [[Glycogen]] depletion will result in a drop in efficiency, and this can be seen in the efficiency value. The graph below shows my efficiency value during a long run, consisting of pacing a 3 hour marathon, then adding on 9 extra miles at a slower pace. You can see my efficiency value staying reasonably constant, with some variation for the hills, until about mile 19. From 19 to 26 you can see my efficiency value gradually dropping due to
glycogen depletion. After the marathon distance you can see some recovery as I refuel somewhat.
[[File:Efficiency and glycogen depeletion.jpg|none|thumb|500px|Efficiency value over a 35 mile run.]]
Assuming you know the distance you ran, your average
heart rate and the time it took, you can calculate your efficiency. If you know your resting heart rate, enter that as well to optimize the calculation.