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Big Question: Why does it hurt so much when I stub my toe?

The expert: Chris Geiser, clinical assistant professor of exercise science and director of Marquette's athletic training program in the College of Health Sciences

"This is not as straight forward a question as you might think. There are a number of factors to consider.

"First, our feet and hands are our interface to the world. As such, they are highly innervated with nerve endings that provide sensory feedback to our central nervous system, which uses this information to guide our actions. With our toes and feet, this is as simple as sensing the shape of the ground, the incline, the pressure that our shoes create on our feet, or the slipperiness of the surface we are standing on all very important information if we are to successfully navigate our world.

"However, all of these nerve endings are capable of relaying pain sensations to our central nervous system when an insult occurs. Furthermore, our brain gives that type of information from our feet the highest priority if we are walking onto or into an unsafe or potentially hazardous place, that is critical information for the brain to deal with. Hence, stubbing your toes hits a densely populated area of nerves that gets high priority in conveying the pain information to our brains.

"Secondly and related to the first point, there is very little tissue in our toes to absorb this type of impact. Much like hitting our shin, there is no fatty tissue or muscle tissue overlying the bones in the toe to cushion the impact. Every bit of the kinetic energy created in moving our legs forward is absorbed by the skin and bone of the toe, resulting in very high compressive forces on the many nerve endings that reside there. Because the foot is at the end of the longest lever system in the body the leg feet tend to be moving much faster than any other part of the body when they come into contact with an unknown object. For these same reasons a pitcher can throw a baseball 90-plus miles per hour and a soccer player can strike the ball at roughly the same speed; the further away from the axis of rotation, in this case our hip, the faster the end of that segment is moving. Add the mass of our entire leg to this equation, and there's a large mass applying force to the toe at a great velocity in a small area not capable of adequately dissipating that impact. OUCH!

"The last part of this explanation comes from an evolutionary perspective. In the not so distant past, infections killed many people. Stubbing a toe can open wounds on the feet, which are constantly in contact with the bacteria-laden environment. It has been suggested that individuals who received lots of sensory information from their toes were less likely to strike them, creating an evolutionary advantage for people blessed with this type of sensory information. So there are many components to this amazingly painful question."


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Comments


Comment by dave rogers at Aug 04 2012 04:05 pm
The "last part of the explanation" is most significant, I think. Evolutionarily, immobile humans were at a terminal disadvantage when it came to survival. Every horror movie viewer knows that those who lose the ability to walk, lose their lives.
This had to be one of the quicker selective traits to dominate: more nerves in feet = survival.
Comment by Pedro at Aug 05 2012 09:46 pm
Surely the last part, evolution is the reason for all of our current body configuration!? =o
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