# Changes

## Relative Running Economy

, 19:13, 26 December 2011
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==Measuring Efficiency==
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.]]
==The Calculator==
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.
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==What do the efficiency numbers mean?==
The number reflects how many times your heart beats when you run a mile. The higher the number, the more efficient you are running and the less often your heart is beating over the distance. Because the numbers are based around your heart beat, they are mostly useful for comparing your runs or comparing parts of the same run, rather than for comparing different runners' performance.
===Changes in efficiency ===
There are a number of reasons why your efficiency can change.
* Obviously changes in your running economy will change the efficiency numbers. For instance, a higher [Cadence] should improve your economy and increase your efficiency numbers.
* Running up hill or downhill will dramatically change the energy cost of running, so your efficiency numbers will change. If you want to compare you efficiency running uphill or downhill, it's best to compare numbers from the same slope.
* Dehydration will cause your heart rate to rise for the same work effort. Looking at changes in efficiency can be used to detect dehydration.
* If you look at your efficiency numbers for speed work, your heart rate will tend to lag behind your work effort. If you change from running at a 9 min/mile pace to a 6 min/mile pace, it will take time for your heart rate to rise up in respond to the extra demands. Likewise, dropping your pace will have a similar lag before your heart rate drops.
==A more impressive alternative==
[[Alternative Efficiency Calculator]] uses age, gender, and weight to calculate Calories consumed, and therefore the absolute efficiency. While this is more impressive and allows for comparison between runners, it makes quite a few assumptions in the calculations. If you know your VO<sub>2</sub>max, this calculation becomes somewhat more accurate, but should still be considered only a rough approximation.
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