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There are several components that make up running ability, including [[VO2max|V̇O<sub>2</sub>max]], and economy. [[VO2max|V̇O<sub>2</sub>max]] is the ability of our bodies to generate energy for running and is the focus of a lot of our training. Running Economy is how far and fast you can run with a given amount of energy. Good economy is a critical part of running, and [[Cadence]] is one element I recommend runners focus on. (For the financial cost of running, see [[The Cost of Running]].)
=The Importance of Improving Running Economy=
Running Economy can vary by as much as 30% between runners of a similar [[VO2max|V̇O<sub>2</sub>max]]<ref name="Daniels-1985"/>. The two charts below show the [[VO2max|V̇O<sub>2</sub>max]] and running economy of Paula Radcliffe over a 10 -year period<ref name="Jones2006"/>. Over that time Paula Radcliffe's race performance dramatically improved even though her [[VO2max|V̇O<sub>2</sub>max]] did not. This suggests that for elite athletes at least, improvements in running economy are critical.
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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). Such testing would require controlling the time of day, day of the week, diet, and footwear for each test<ref name="Pereira-1997"/> as well as specialist equipment that is not available to recreational runners. (Systems such as Cosmed's K5, PONE, and VO2 Master's VM Pro are becoming available, but cost thousands of dollars. Because this is not practical, the best measure we have of energy consumption is our [[Heart Rate]]. This is far from perfect, as [[Heart Rate]] [[Heart Rate Drift| can vary for other reasons besides supplying O<sub>2</sub> for energy production]]. However, I believe it is a useful approximation and so I developed the simpler "Relative Running Economy." I've created an improved version called "HR-Pwr" which used the power estimate from [[Stryd]] to give a more useful estimate.
=HrPwr Estimate of Running Economy=
My initial approach was to use heart rate to estimate energy cost and distance covered to measure the effort. This works okay on the flat, but is thrown off by changes in elevation. The [[Stryd]] footpod estimates the power output based on pace and elevation changes, which solves this problem nicely. It also gives the possibility of comparing data from running with cycling, though I've found the Stryd power estimate to be much higher for a given perceived effort than cycling. The formula I use is milliwatts per Kg per heartbeat, which I've called [[HrPwr]] (It's available as a [[Connect IQ]] data field.)
=Relative Running Economy=
This Relative Running Economy calculates a value based on how many heart beats are used for the distance covered. The formula that is shown below and there are more details at [[Relative Running Economy]].
The calculated [[Relative Running Economy]] cannot easily be used to compare different runners. It can be used as to track how your running economy is improving over time, though it is also influenced by changes in fitness. Over the weeks and months of training your Relative Running Economy should gradually improve. For instance, I've seen my RRE go from 110-120 to 130-150 over a period of a few months. Sadly, I've also seen my RRE drop when I put on body fat (see [[Weight Loss and Performance]].) This evaluation of my fitness this proved to be remarkably useful to me.
=Relative Running Economy to detect Glycogen Depletion=
Another use for the Relative Running Economy 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 glycogen depletion causes more fat to be burned, and fat requires more oxygen to provide an equivalent amount of energy. 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|300px|Efficiency value over a 35 mile run.]]
=Billat's Cardiac Cost=
Veronique Billat produced a similar formula called "Cardiac Cost" in a research paper on marathon pacing<ref name="BillatPalacin2020"/>. The formula
Cardiac Cost = (Heart Rate / Speed) / 6000
Where the speed is in Km meters per minute. The Billat's formula does not adjust uses [[Heart Rate]] on its own rather than adjusting for [[Resting Heart Rate]]. This formula is inverted, because it's looking at cost rather than efficiency. However, but otherwise will result you can see the similarity below. (Note that Billat's paper shows the speed in both meters/minute and Km/minute. I queried this with Billat by email and confirmed this should be meters/second.) [[File:RRE and CC.jpg|center|thumb|600px|Top to bottom: relative running economy, cardiac cost, heart rate, pace (form [[Stryd]].]]
=References=
<references>
<ref name="Pereira-1997">MA. Pereira, PS. Freedson, Intraindividual variation of running economy in highly trained and moderately trained males., Int J Sports Med, volume 18, issue 2, pages 118-24, Feb 1997, doi [http://dx.doi.org/10.1055/s-2007-972606 10.1055/s-2007-972606], PMID [http://www.ncbi.nlm.nih.gov/pubmed/9081268 9081268]</ref>
</references>