Running economy is the amount of oxygen consumed at any given velocity. Reduced need for oxygen at a given speed means economy has improved because less energy is needed to maintain that velocity. A new study in the Journal of Strength and Conditioning Research explored the relationship between the lower body and running economy.
Running Economy and the Lower Body
Even with similar VO2 max and experience level, it’s possible for two runners to have different levels of running economy. Since many researchers now believe that running economy is more important than VO2 max to predict running performance, it’s a necessary attribute to develop.
There are several factors known to influence running economy. The new study focused on the lower body. The researchers examined numerous physiological, biomechanical, and neuromuscular factors of the legs in 63 men and women to get answers.
Women had consistently better running economy at every velocity, but this seems to have been due to their smaller size. When relative economy was considered, the men fared better. The researchers found no clear delineating factors that could define the difference between running economy in individuals or between men and women.
Two major factors did stand out as consistently impacting running economy, although they affected it differently depending on the individual. Those were lower body muscle and tendon stiffness and the moment arm of the ankle.
Muscle and Tendon Stiffness
Stiffness refers to the degree of slack in the muscles and tendons as they store and utilize elastic energy. In the case of this study, high stiffness was a good thing, because it correlated with greater ability to store energy. Imagine the difference between a brand-new rubber band and a well used one that no longer has the same stretch. Interestingly, despite more flexible ankles on average, women proved to have greater Achilles stiffness.
It is theorized that stiffness can be improved, but how to do it is not presently well understood. Since plyometrics have a well-demonstrated relationship with improvements in running, it’s possible that they are a method for developing this quality and thus improving running economy.
The other quality, moment arm, is one that can’t be changed. Moment arm is a term in mechanics, and in this case it is measured as the approximate distance from the bump of your ankle joint to the back of your Achilles tendon. A shorter moment arm creates a more rapid stretch, and thus more elastic energy. Being smaller, women also had superior moment arms.
These two qualities had a huge impact on running economy, but they did not fully explain the forces at play. From a lower body perspective, women have all the goods for prime running economy, but still have lower economies pound-for-pound when compared to men. While more study is needed, for now, working on your Achilles and calf stiffness may improve your running performance, regardless of gender.
1. Kyle Barnes, et. al., “Lower-Body Determinants of Running Economy in Male and Female Distance Runners,” Journal of Strength and Conditioning Research, 28(5), 2014
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