Studies have shown that less flexible runners have greater running economy. With so much focus on the importance of stretching you may be wondering how this makes sense. Why stretch if it decreases running economy and why is running economy improved if you are less flexible? Is stretching making us slower runners?
Running economy is how efficiently a person uses oxygen at a given pace. So two people may be running at the same pace but the person who is more economical will be using less oxygen
To understand why flexibility can be detrimental to running economy we need to understand what is meant by flexibility and how the elastic property of muscles and tendons can be taken advantage of to improve our ability to run.
Flexibilty
The studies measured passive or static flexibility. Static flexibility is what most people think of when they think of stretching – ie reaching forward and holding a stretch. Passive range of movement is where somebody moves your limbs for you to see how much range of movement you have.
It is obvious when watching middle distance runners on a track that they have good flexibility. Their large stride length and the way their heels come up and almost kick their butts indicates flexibility greater than average. The flexibility they possess is dynamic and is very different to static or passive flexibility.
Elasticity in Running
Muscles and tendons can be stretched in a similar way to a rubber band. Once they have been stretched they can “spring” forward in the same way a rubber band does when released. In running the energy required to stretch the band comes from momentum, gravity and landing forces so is essentially free, i.e. at no cost to the body.
However unlike a rubber band, the time between stretching and release must be short. The more time between stretching and release, the more energy lost via heat mechanisms and therefore less “spring” occurs in the muscles and tendons. This is why being more flexible can hurt your running economy.
A very flexible runner has muscles and tendons like long skinny rubber bands. These take time to stretch back far
enough to store enough elastic energy to fly forward. Unfortunately when we run we have very little time for the stretch to occur as our foot is only on the ground for 0.1-0.3 of a second. The stretch must occur quickly or the potential to store and use elastic energy is lost.
So ideally we would like to train our muscles and tendons to become like short fat rubber bands – needing very little stretching to generate enough force to fly forward.
If you watch a fast runner compared to a slow runner you will see what I mean – the fast runner seems to skim the ground, feet barely touching whereas the slower runner will crash into the ground with every step and then heave themselves off again with great effort. The faster runner is in fact using less energy ( more economical) since much of the energy required is coming from elastic energy.
Can we improve the ability of our muscles and tendons to use elastic energy?
There are two forms of training that can improve the bodies ability to use elastic energy – plyometric training and dynamic stretching.
I have discussed plyometric training in an earlier blog.
How can dynamic stretching be of benefit when I have just mentioned that less flexible runners have greater economy?
Dynamic stretching (discussed here) is not designed to increase the passive range of movement in a joint. It is used to either increase dynamic flexibility and/or increase the elastic recoil of muscles and tendons and therefore will improve running economy.
A good dynamic flexibility program will train muscles and tendons to work dynamically, storing and releasing elastic energy through the range of movement required in a particular sport.
