Tactile Sensitivity of the Sole of the Foot as a Factor of Shoe Comfort
The tactile sensitivity of feet, considered to be one of the factors influencing shoe comfort, was examined in order to develop a system that assess shoe comfort, without actually trying on shoes. The tactile sensitivity of the feet of 84 healthy Japanese adult males and females between the age of 18～39 (males 53, females 31) was measured and the following 4 points were examined by nonparametric tests:
- Gender difference: Does foot sensitivity vary between males and females?
- Inter-location difference: Does foot sensitivity vary across the regions of the foot?
- Is there any typical sensitivity pattern in particular foot regions?
- Is the sensitivity consistent across the sole of a single foot?
How to Measure Tactile Sensitivity
Tactile sensitivity was quantified by the pressure sensory threshold which was measured using the Semmes-Weinstain monofilament testing method.
- In this method, the pressure sensory threshold is measured by using 20 testers to which thin nylon filament of a fixed length is attached. Each monofilament has a known diameter and buckling force.
- The examiner poked the subject's foot skin with the tip of a filament. The pressure sensory threshold of the stimulated location was determined as the buckling force of the filament [log0.1mg] when, without looking at their foot, the subject correctly recognized where the filament was contacting.
- By considering the contact areas between feet and shoes, the pressure sensory thresholds were measured at 17 foot locations. These locations were measured in a random order.
Gender difference: Does foot sensitivity vary between males and females?
The results were as follows:
- There was no significant gender difference found for tactile sensitivity (Mann-Whitney's U test).
- Significant differences in tactile sensitivity were found between 17 locations. (Friedman's test, p < 0.01).
- A typical pattern was found for the inter-location differences in sensitivity. (Ranks of Friedman's test)
- The order of sensitivity, from least sensitive to most sensitive was: the plantar region excluding the plantar arch (p-5 to -8, p-10 to -12), plantar arch (p-9) and side region (s-13 to -17), and dorsal region (d-1 to -4).
- The areas that bear high weight loads tend to be less sensitive than areas that do not bear appreciable weight.
Is the sensitivity of the sole consistent across the same foot?
Although individual differences can be found, with the exception of the arch, the sole of the foot is a relatively unresponsive region when compared to other foot parts.
We studied the relationships of the tactile sensitivity of 3 parts of the sole to find, for example, if a person with a more unresponsive posterior sole also has a less sensitive anterior sole (Speaman's rank correlation coefficient).
- It was found that the correlations between regions are weak. The plantar region was a less sensitive region as a whole, but not uniformly so.
- Shoe comfort can be improved individually by harmonizing the material property of a shoe sole with the sensitivity characteristics of an individual's sole.
- For example, an insole combining materials of different properties for posterior, middle, and anterior parts of the sole, may be a simple solution for improving shoe comfort.
- M. Dohi, M. Mochimaru, M. Kouchi : The Distribution of the Tactile Sensitivity of a Foot and the Softness of its Skin, Proceedings of the 32nd Convention Meeting of Kanto Branch of the Japan Ergonomics Society 2002, pp90-91, 2002
- M. Dohi, M. Mochimaru, M. Kouchi : The Distribution of the Tactile Sensitivity of a Foot and the Softness of its Skin, Proceedings of SICE SI 2002, Volume 3, pp189-190, 2002
- M. Dohi, M. Mochimaru, M. Kouchi : The Tactile Sensitivity and Elasticity of the Sole of the Foot as Factors of Shoe Comfort, Proceeding of IEA2003, 2003
- M. Dohi, M. Mochimaru, M. Kouchi : Distribution of Tactile Sensitivity and Elasticity in Japanese Foot Sole, Kansei Engineering International, Vol.5 No.2 pp9-14 2004