Relative Running Economy

1 Introduction

There are two components to running ability; fitness and economy. Fitness is the ability of our bodies to generate energy for running and is the focus of a lot of our training. 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 focus on.

2 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 O₂ we consumed and how much CO₂ 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 O₂ for energy production. However, I believe it is a useful approximation.

3 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.

4 The Garmin Utility

If you have a Garmin GPS, this utility will analyze the TCX files to calculate efficiency. You can download it from http://fellrnr.com//Utilities/GarminEfficiency/GarminEfficiency.exe (you'll need .NET 4.0 if it's not already installed.)

5 The Efficiency Calculation

The formula that is used is

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

6 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.

6.1 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.

7 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 VO₂max, this calculation becomes somewhat more accurate, but should still be considered only a rough approximation.