Last week we showed how you can easily convert an existing training schedule into a training schedule based on power. The great thing is that you can personalize it if you know what your running efficiency is.
With the help of a running power meter, you can attach a value to your running efficiency. And if you have a value, you can use gait training to improve your running performance. This is not always easy. Habits are hard to change.
The value we’re talking about is the specific energy, the amount of energy you need per kilogram of body weight to run a kilometer. The commonly used term is Energy Cost of Running (ECOR). The corresponding unit is kJ/kg/km. A typical trained athlete who has had running training has an ECOR of 1.04 (including running wind, on a virtually windless day). For the newest shoes the ECOR might be 4% less: 1.00 kJ/kg/km. A recreational runner may be at 1.10 or even higher, which means he or she uses relatively more energy to perform the same as the skilled athlete.
Measuring is knowing
We explained how to calculate your ECOR last week. You calculate this from your power data from fast training sessions and races over 5 to 15 km on days with little wind, on a flat course with hard surface. When the wind blows and on a hilly course, running takes more energy. The calculated ECOR may be interesting, but is not suitable as a measure of your running efficiency.
ECOR and RE Relationship
Traditionally, runners know the concept of Running Efficiency (RE). Running Efficiency is defined as the specific oxygen consumption (in ml O2/kg/km). It can be determine during a treadmill test at a sports medical advisory centre (SMA).
There is a fixed relationship of the specific energy consumption ECOR (in kJ/kg/km) with the specific oxygen consumption RE (in ml O2/kg/km). The energy production of 1 ml O2 is equal to 19.5 Joule and the muscle efficiency, 25% for top athletes. A RE of 201 ml O2/kg/km corresponds to an ECOR-value of 201*19.5*0.25/1000 = 0.98 kJ/kg/km.
This 0.98 is less than the ECOR 1.04 kJ/kg/km that we mentioned earlier. In the 1.04 the running wind is also comprised. The 0.98 applies to running on a level treadmill.
The ECOR and the RE are not for everyone and in all conditions equal to 0.98 kJ/kg/km and 201 ml O2/kg/km. There are many articles and books that describe that the RE may be lower or higher. Some marathon runners, especially Kenyans and Ethiopians, have a very efficient running style, which means that they consume less oxygen and therefore have a low RE.
Together with the Radboud University in Nijmegen (the Netherlands), we have done practical research into the relationship between ECOR and RE. In that study, we found that untrained runners had a muscle efficiency (metabolic efficiency) of 23%. The trained runners were with 24% significantly more efficient. This means that when they run with the same power they needed 4% less oxygen than the untrained runners. Elite athletes have a muscle efficiency of 25% and therefore run even faster.
As an example we give the ECOR of the top athletes who assisted Eliud Kipchoge to run the marathon under 2 hours (Vienna 1:59:40): 0.93 kJ/kg/km. This is 5% better than 0.98!
With a running power meter with the accuracy of a Stryd, you can express your running efficiency in a number, the ECOR. And since you now know that ECOR has a direct relationship with the RE, you don’t necessarily have to go to the exercise laboratory of a sports medical centre anymore. And by regularly calculating your ECOR, you can now check for yourself whether your running training is paying out or not.
According to the literature, the running efficiency is determined by our physique and our running style. The theory of biomechanics shows the following factors for the physique:
- Weight legs (light/slender lower legs are favorable)
- Lever Achilles tendon (small feet are beneficial)
- Leg length (long legs are beneficial)
- Hip angle (narrow and flexible hips are beneficial)
We cannot control these factors ourselves. At most, by losing weight, we can remove some excess fat from our legs and calves. However, we can try to get our joints, especially ankle, knee and hip, as flexible as possible through exercises and running training.
The most concrete factor we can work on to improve running efficiency is the running style. This includes, for example, a short and springy ground contact, avoiding heel landing, using the arms to support the running movement and stretching the toes at the push-off. Runners do differ in opinion on what is the optimal running style with the highest efficiency. The factors that we can most easily influence ourselves are the cadence, the stride length and the vertical oscillation.
How much effect does ECOR have?
For this article, we calculated the potential effect of a higher or lower ECOR. In addition to the standard value of 1.04 kJ/kg/km (including running wind) we also took 2 alternatives:
- a higher ECOR of 1.10 kJ/kg/km (this higher ECOR means that the runner consumes more energy and more oxygen and therefore runs less efficiently)
- a lower ECOR of 1.00 kJ/kg/km (this is a low value that we see in the highly efficient elite athletes)
In the table below we show what this would mean for the achievable speed and duration of our character Marathon Man who runs 3:30 on the marathon and weighs 70 kg. You can see the effect of the ECOR on the race times. For fast times it is important to run as efficiently as possible.
Our book ‘The Secret of Running’ is for sale in our webshop. Also available in German as ‘Das Geheimnis des Laufens’, and in Italian as ‘Manuale completo della corsa’.