There are several components that make up running ability, including V̇O₂max, and economy. V̇O₂max 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.)

Running Economy can vary by as much as 30% between runners of a similar V̇O₂max^[1]. The two charts below show the V̇O₂max and running economy of Paula Radcliffe over a 10-year period^[2]. Over that time Paula Radcliffe's race performance dramatically improved even though her V̇O₂max did not. This suggests that for elite athletes at least, improvements in running economy are critical.

Paula Radcliffe's V̇O2max

Paula Radcliffe's Running Economy (V̇O2 consumption at 16 Km/hr, 6:00 min/mile)

There are several approaches that may improve your running economy. For details see The Science of Running Economy.

• Weight Loss. Losing weight can dramatically improve your running economy, as shown in my Running Calculator. (For those paying close attention, running economy is often normalized to the runner's weight, so that specific metric won't improve.)
• Cadence. The right Cadence is a key to efficient running and avoiding injury.
• Running Form. As well as Cadence, there are other aspects of Running Form that can improve running economy. For instance, step width can change running economy by 11%^[3].
• High Intensity Interval Training. There are several studies that have shown that High Intensity Interval Training improves running economy.
• Heavy Weight Training and Plyometrics. Studies show these interventions can improve running economy by as 4-5%. Heavy weight training is 10 or less repetitions at 70% of 1 repetition maximum, using leg press, squats, etc. Plyometrics are explosive movements, such as Jumps. See Plyometrics for more details.

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 O₂ we consumed and how much CO₂ 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^[4] 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 can vary for other reasons besides supplying O₂ 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.

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.)

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.

Total Beats = (Average Heart Rate – Resting Heart Rate) * Time in Minutes
Work Per Mile = Total Beats / Distance in Miles
Efficiency = 1 / Work Per Mile * 100,000

Note that the difference between Heart Rate and Resting Heart Rate is used to calculate the heart beats used for movement. Ideally the Heart Rate for standing would be used, but typically Resting Heart Rate is taken seated or lying down.

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.

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.

Efficiency value over a 35 mile run.

Veronique Billat produced a similar formula called "Cardiac Cost" in a research paper on marathon pacing^[5]. The formula

Cardiac Cost = (Heart Rate / Speed) / 6000

Where the speed is in meters per minute. Billat's formula 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, 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.)

Top to bottom: relative running economy, cardiac cost, heart rate, pace (form Stryd.

1. ↑ JT. Daniels, A physiologist's view of running economy., Med Sci Sports Exerc, volume 17, issue 3, pages 332-8, Jun 1985, PMID 3894870
2. ↑ Andrew M. Jones, The Physiology of the World Record Holder for the Women's Marathon, International journal of Sports Science and Coaching, volume 1, issue 2, 2006, pages 101–116, ISSN 1747-9541, doi 10.1260/174795406777641258
3. ↑ PU. Saunders, DB. Pyne, RD. Telford, JA. Hawley, Factors affecting running economy in trained distance runners., Sports Med, volume 34, issue 7, pages 465-85, 2004, PMID 15233599
4. ↑ 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 10.1055/s-2007-972606, PMID 9081268
5. ↑ Véronique Louise Billat, Florent Palacin, Matthieu Correa, Jean-Renaud Pycke, Pacing Strategy Affects the Sub-Elite Marathoner's Cardiac Drift and Performance, Frontiers in Psychology, volume 10, 2020, ISSN 1664-1078, doi 10.3389/fpsyg.2019.03026