Inflexibility & Running Economy

Physiology Running Form

 

Being flexible get all the glory.

Yet, is there such a thing as too much flexibility?

 

There are multiple studies available that have looked at how increased flexibility may influence running economy. Three of them are below.

First, what is running economy?

Ross Tucker explains it as “analogous to cruising-efficiency in a car (not entirely, but we’ll get there!). If you think of a human, we can measure the maximum volume of oxygen that can be used, and this is called the VO2 max or VO2 peak. The problem is, for most running events (certainly above about 5000m), runners don’t use this “maximum” amount – they are sub-maximal. And so therefore, a more important measure becomes the volume of oxygen that is used up when the runner is going at a sub-maximal speed. So to return to our fuel analogy, it’s saying that the car is cruising along at a speed lower than maximal, and we’re interested in how much fuel it uses per kilometer.

Back to how flexibility may influence how economic your body is or is not..

The first study we’re going to look at was published in the International Journal of Sports Medicine and looked at looked at the relationship between running economy and lower body flexibility in thirty-four international standard male distance runners. Their results “suggest that the least flexible runners are also the most economical. It is possible that stiffer musculotendinous structures reduce the aerobic demand of submaximal running by facilitating a greater elastic energy return during the shortening phase of the stretch-shortening cycle.

Another study from the Journal of Strength and Conditioning Research states that “Flexibility has been controversially suggested as one of the biomechanical factors contributing to the variability observed in running economy among distance runners.” and they compared the classic sit and reach flexibility test to running economy in eight collegiate runners. They also found that “less flexible distance runners tended to be more economical, possibly as a result of the energy-efficient function of the elastic components in the muscles and tendons during the stretch-shortening cycle.

Finally, our third study from the ACSM’s Medicine Science in Sports and Exercise looked at measures of limb and trunk flexibility to compare to running economy and found that “Although speculative, these results suggest that inflexibility in certain areas of the musculoskeletal system may enhance running economy in sub-elite male runners by increasing storage and return of elastic energy and minimizing the need for muscle-stabilizing activity.

So basically,

Having greater flexibility may reduce your running economy because your body may require greater stabilization and receive less “free” elastic energy return.

Think of this elastic energy return like shooting with a sling-shot. If the sling is too loose you don’t get as much oomph when released, but if it is too stiff you can’t pull it back as much.

Further Thoughts,

Two things I like to keep in mind about flexibility are that “Flexibility is about relaxation, not stretching” and this means that the ability to have a good range of motion is not about stretching the tissues, but allowing those tissues to relax and be stretched.

Second is that “too much mobility without adequate stability is dangerous”. Consider the pronating ankle, which moves inwards when your foot is on the ground. If you have excessive mobility it moves inwards too much, may cause you ankle discomfort, and is referred to as over-pronation. However if you develop adequate foot strength to control this pronation (not with a supportive shoe) you can reduce the degree of pronation to a more acceptable amount.

Plyometrics are an incredibly sport specific method of strengthening the legs and improving how they move.

TL:DR The least flexible runners are also the most economical. It is possible that stiffer musculotendinous structures reduce the aerobic demand of submaximal running by facilitating a greater elastic energy return during the shortening phase of the stretch-shortening cycle.

 

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