Natural Running Efficiency: Using Elasticity in the Lower Leg
28 July 2011
By Douglas Bertram, MTCM, L.Ac.
Several studies have shown a direct link between Achilles tendon length and the amount of energy the tendon can store. The tendo-muscular structures of the posterior lower leg often become shortened by wearing shoes with an elevated heel. Shorter tendo-muscular structures significantly reduce the elastic recoil potential; therefore it is recommended to wear level running shoes. The ramp angle or heel-toe drop is determined by measuring the difference of height between the heel and the forefoot of a shoe. A heel-toe drop of more than 3-4mm will start to change the ability for the tissue of the posterior leg to store and release energy.
The plantar fascia also acts as an important spring. When landing on the mid-foot/forefoot with the foot under the center of mass, the longitudinal arch should lengthen. This lengthening of the arch stretches the plantar fascia and aids in shock absorption as well as increased elastic recoil. By releasing the stored energy from the plantar fascia, significantly less active muscular effort is needed to lift the foot back off the ground. Less active push off means less wasted energy. In order for the arch to naturally lengthen there must be enough room in the shoe. Ridged structures “supporting” the arch do not allow for this natural motion. Stiff running shoes and rigid hard plastic orthotics might have a place for some foot pathologies, but will significantly alter the natural spring mechanics of efficient running.
A slow cadence has the same effect of reducing efficiency. Optimal cadence is around 180 steps per minute because this is the speed of which tendon is able to store and release energy. It is the frequency of elastic recoil. Shoes that are made of soft “cushioned” EVA foam will slow down your cadence because it interferes with the body’s ability to sense the ground. The more “cushion” between your foot and the ground, the more time your foot will stay on the ground due to a reduction in afferent feedback. The quicker the foot can find the ground, become stable and release, the quicker your cadence will become. Most people will speed up their cadence by 10 -15 steps per minute by running barefoot or in lightweight firm shoes (firm under the ball of the foot, not the arch). Look for a shoe that offers a good amount of protection, yet gives good afferent feedback. This will help you take advantage of the passive energy of elastic recoil and make you a more efficient runner.
Finding The Proper Fit
Standing with your heels pulled to the back of your shoes, you should have at least a thumb’s width in front of your longest toe. Many people wear their shoes too short, too narrow and laced too tight. The ball of your foot freely spreads upon loading, allowing the spring-like mechanism of the longitudinal arch to lengthen, and the transverse arch (from the 1st to the 5th metatarsal head) to widen. The spreading of the foot aides in both shock absorption and stabilization, as well as helps facilitate the mechanics of elastic recoil. If the shoe is too narrow and the arch too stiff, natural motion of the foot is prevented.
Lacing a shoe too tightly is a habit that forms from running in a shoe with a significant ramp angle, where the foot tends to slide forward, thus creating the need to lace tightly to prevent this motion. When transitioning into a level shoe, there is not the same need to stop this forward motion. The foot needs room to rise and fall to be efficient.