Carbon Graphite Shoe Inserts – can I use a single insert or are they better as a pair?

How do carbon graphite insoles affect gait?

Part 1 – Legs and levers

A common question that we hear from customers is whether a carbon graphite shoe insole can be used as a single shoe solution or should they purchase as a pair to balance gait.  Does a single carbon graphite insert effect gait in a detrimental way?  Let’s take a closer look at carbon graphite shoe inserts and their effect on gait.

How do carbon graphite shoe insoles affect the lever mechanics of the lower extremity?

Walking can be described as a controlled forward fall, regulated by a lever arm we know as the leg, ankle, and foot.  Levers typically include three parts; the effort arm, the resistance arm, and the fulcrum.  In this example, the leg is the effort arm, primarily dominated by the function of the soleus muscle.  The foot becomes the resistance arm of the lever where the biomechanical force generated by the effort arm is manifested.  The ankle is the fulcrum, the hinge that translates the force generated by the effort arm to the resistance arm to create work.  We call this work walking.

In the leg, the soleus muscle is the slow twitch muscle that dominates the effort arm and acts to decelerate the forward motion of the tibia as it moves forward over the foot during the stance phase of gait.  During stance phase, the soleus muscle is undergoing eccentric muscle contraction – providing force while lengthening.   

How does a carbon graphite shoe insert effect the lever mechanic of the lower extremity? 

Think of carbon graphite inserts as a brace for the foot much akin to a rigid shank in the shoe – the shank being the portion of the shoe extending from the heel to the ball of the foot.  A carbon graphite shoe insert is intentionally used to stiffen the shank.  Referring back to lever mechanics, use of a carbon graphite insert effectively lengthens the resistance arm of this lever.  Lengthening the resistance arm increases the power of the entire lever.  The result becomes:

• Increased duration of the stance phase of gait
• Increased force to the forefoot at the toe-off phase of gait
• Empowerment of the soleus muscle (increased duration and amount of eccentric contraction)
• Increased mechanical load applied to the lower leg, knee and upper leg
• Increased mechanical load applied to the hip and lumbar spine

Lengthening of the resistance arm can indeed result in increased load applied to the leg, hip, and back.  Lengthening the resistance arm can also result in prolonging the stance phase of gait, decrease propulsion at toe-off and result in steppage gait.  Steppage gait describes lifting of the foot rather than actively pushing off with the ball of the foot. 

Are these mechanical changes caused by a carbon graphite shoe insert necessarily a bad thing?  Are they detrimental to gait?  In some respects, yes.  But these changes in gait are often off-set by use of what's called a forefoot rocker.

Let’s jump to part 2 of this conversation – rocker mechanics.

Jeff  

Jeffrey A. Oster, DPM 

Medical Advisor
Myfootshop.com  

Updated 3-11-2021

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