Sensitive Soles

As humans age, the less sensitive our feet become. As a result, balancing whilst walking on rough surfaces, like cobblestones, becomes more difficult.

A study in the journal Nature found that calluses from walking barefoot don't reduce how sensitive your foot is.

According to biomechanist Kris D'Août, from the University of Liverpool, the data contains “information that we can use to stay stable. It makes sense to wear shoes that are inspired by the calluses, in the sense that they might have to be fairly hard so they transmit the information from the substrate onto the skin”.

Researchers travelled to Kenya, and measured the thickness of the callus on the bottom of participants’ feet using ultrasound images - like those used to scan unborn babies.

Half of the people regularly wore shoes, and they had very thin calluses. The other half, who often walked barefoot had formed thick calluses on the base of their feet from their toes to the heel.

On top of that, the scientists found that the thicker these calluses are, the more they resisted any indentations into the foot. Which makes sense, the thicker the callus, the harder it will be to put a dent in it.

Then they had to check if a thicker callus reduced how sensitive the participants' feet were. They measured the sensitivity of each participant’s foot using a machine that creates vibrations on the base of each subject’s foot, both at the heel and the ball of the foot.

Special types of cell, called mechanoreceptors, that are present in the outer layer of the skin detect any changes in pressure associated with each vibration. The scientists designed the vibrations to mimic a human being walking on two feet.

The pressure changes during the vibrations are similar to those that a human foot is exposed to when the foot is placed against the floor during walking.

Surprisingly, the researchers found that the thickness of the callus did not have a noticeable effect upon the sensitivity of the skin to the vibrations. D'Août compared calluses with cushioned shoes and commented that the “thick cushioned sole might protect you very well against sharps, but you have a reduced sensation of what is happening beneath your foot sole”.

Why are these results important? D'Août pointed out that we could “help people that are getting older and have reduced sensation naturally” by “learn(ing) from nature”.

Today we have become accustomed to wearing shoes a lot of the time. They keep our feet warm and provide an additional layer of protection from sharp surfaces.

There are also a lot of social aspects associated with wearing shoes. Hopefully with this new set of data, we can adapt the design of our shoes to improve our stability and balance.