Quantifying Running Economy with a Power Meter

The last few decades have seen a revolution in the personal quantification of running performance.

Background of Technology Breakthroughs in Measuring Running Performance

Stop Watch

Timex Ironman Watch

Timex Ironman Watch

The revolution started with sport wrist watches like the Timex Ironman back in the 1980s that allowed athletes to conveniently record and recall split times while running. No coach standing on the side of the track yelling out splits needed.

This gave us instant feedback on time to cover a known distance and thus deriving pace. This knowledge was so handy and useful for interval training on the track for example.

Heart Rate Monitors

Polar Heart Rate Monitor

Polar Heart Rate Monitor

Shortly after the sports watch, came heart rate monitors from Polar that gave us real time insight into our heart rate. The heart rate monitor gives instant feedback on cardiovascular effort. Information on heart rate is useful for monitoring effort to prevent over or under exertion.

Heart rate is very individualized as everyone is different in cardiac capacity and output. Heart rate is a great measure of effort and useful for comparisons between workouts for an individual. It has little value in comparisons between different people. A race is not won by the person with the highest or lowest heart rate, but by the person that is the fastest over the distance no matter what the heart rate.

There is a whole science that has evolved around training using heart rate. And a whole science that has evolved about using heart rate variability to measure health and monitor for adaption to training and over trained states.

GPS

Within a few years after the availability of heart rate monitors was the GPS revolution. One of the first on the market was Garmin with watches that would display running speed (pace), average speed, distance traveled, elevation gain etc. GPS became an extremely useful and convenient technology for directly quantifying running performance.

Power Meters

Next stop and the current stop on the technology train is Power Meters. Bicycles have had Power Meters for a decade or so now, but this technology is just now becoming available to runners.

RPM2 rpm2.com

Stryd stryd.com

The beauty of a power meter is that it gives real time feedback on energy expenditure and physical effort.

In my opinion, power meters will bring on a change and revolution in training as great as heart rate monitors and GPS devices did previously. Having a power meter will change the way you train.

For bicycles, the use of power meters has focused on maximizing power output and maintaining power output during a workout or race. Less attention has been paid to efficiency or economy. This is because on a bike, economy is less dependent and in control of the biker and more dependent on the bike hardware.

For running, efficiency and economy is primarily in the control of the runner. So it is natural to want to focus attention on economy and maximize economy as well as power output. So the question becomes, how does one attain a useful value of running economy from a power meter?

Proposed Useful Mathematical Formula for Running Economy

Here is my proposal for a useful mathematical formula for running economy. It is only possible to get a real time value of running economy when you couple a power meter with a GPS device. Once you know your instant value of your running economy, you can experiment and modify the way you run and get real time feedback on what helps and what hinders your running economy. This is my wish list for the companies that are developing power meters for runners.

If I still had an engineering business and a budget I would develop a watch size wearable GPS device that could continuously monitor and display a value of running economy. A shoe or foot bed with force plates and accelerometers would have to communicate wirelessly (blue tooth) with the watch. An accelerometer clipped to the waist and one in the watch would add more data refining the calculation of power. Once you have pace from the GPS and power from the power meter you can derive running economy. The definition of Running Economy becomes:

Running Economy is Ratio of Pace to Power

Running Economy = Pace / Power

To get values of Running Economy that are simple to work with, I propose using SI units of Meters for distance, Watts for Power and Pace expressed in Meters per Minute.

Using these units will typically yield values near but less than 1.0. Some may prefer to represent this as a % by multiplying by 100.

Some examples are helpful to illustrate the calculations. These examples are derived and simplified from some actual personal measurements and tests.

Example A

  • Running Economy of 0.75
  • Pace of 300 Meters per Minute (5:20 per Mile)
  • Power of 400 Watts
  • Running Economy = 300 Meters per Minute / 400 Watts = 0.75

Example B

  • Running Economy of 0.67
  • Pace of 240 Meters per Minute (6:40 per Mile)
  • Power of 360 Watts
  • Running Economy = 240 Meters per Minute / 360 Watts = 0.67

Example C

  • Running Economy of 0.80
  • Pace of 200 Meters per Minute (8:00 per Mile)
  • Power of 250 Watts
  • Running Economy = 200 Meters per Minute / 250 Watts = 0.80

It is interesting to note that this particular runner is less efficient at a moderate pace as compared to a fast pace and an easy pace. A possible explanation (this is from firsthand experience of this particular runner’s training history) is that the runner had developed better economy at the paces that they spend the most time training at. In this case, fast interval running is done at 5:20 pace (300 Meters per Minute) and easy running is done around 8:00 pace (200 Meters per Minute). This particular runner is less experienced at running 240 Meters per Minute and has not naturally developed their economy at this particular pace.

Obviously power will go up with the weight of the runner lowering running economy. So it may be helpful to normalize Running Economy by Weight. Doing this, Running Economy by Weight can be compared between different runners.

These are just some preliminary thoughts on Running Economy. It will be interesting to see what products and their features become available in the next few years. It is my desire to see a real time read out of Running Economy on a watch. With that information, a runner has feedback on what form, cadence and other adjustments maximize their economy.

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About Bridger Ridge Run

The Bridger Ridge Run blog is an information portal for all those seeking to learn more about the Bridger Ridge Run event held every second Saturday of August in Bozeman Montana. This blog contains notifications about important registration dates and deadlines, history of the event, training advice and other stories and entertaining tidbits of information about the Bridger Ridge Run.
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