The plantar-foot comprises viscoelastic tissue of several different layers. Previous studies have investigated properties such as Pressure Pain Threshold (PPT), Pressure Discomfort Threshold (PDT) and Stiffness of the plantar foot. However, only a handful of studies have evaluated the viscoelastic properties. Even though past studies have recorded the properties of the plantar-foot, it is not possible to compare the results across the studies due to testing location mismatches.

In this thesis a generalizable grid was developed for the foot using anatomical landmarks. The grid had 95 points, and each point was tested using an automatic tissue tester with a 0.5 cm² soft edge cylindrical probe at an indentation speed of 1mm/s. Reliability of the grid was tested by measuring and co...[ Read more ]

The plantar-foot comprises viscoelastic tissue of several different layers. Previous studies have investigated properties such as Pressure Pain Threshold (PPT), Pressure Discomfort Threshold (PDT) and Stiffness of the plantar foot. However, only a handful of studies have evaluated the viscoelastic properties. Even though past studies have recorded the properties of the plantar-foot, it is not possible to compare the results across the studies due to testing location mismatches.

In this thesis a generalizable grid was developed for the foot using anatomical landmarks. The grid had 95 points, and each point was tested using an automatic tissue tester with a 0.5 cm² soft edge cylindrical probe at an indentation speed of 1mm/s. Reliability of the grid was tested by measuring and comparing the PPT, PDT and stiffness. Between subjects similarity of the grid was investigated using Morisita’s similarity index. PPT and PDT showed a Morisita’s similarity index value higher than 0.9 in male participants and higher than 0.75 in female participants. Spatial auto correlation was calculated using Moran’s I index. PDT and PPT had Moran's I index values of 0.7. K means clustering was used to developed maps for PPT, PDT and Stiffness over the plantar-foot surface.

The perceived feeling of hardness was tested over the plantar-foot surface in another experiment. Three Ethyl Vinyl Acetate (EVA) materials of different hardness were used for the four regions of Heel, Mid-foot, Forefoot, Toes. The heel hardness had a significant (p<0.05) influence on the perceived hardness rating of the other regions. When harder materials were in the heel region, regardless of what materials were in the other regions, participants felt a higher perceived hardness and vice-versa.

The viscoelastic properties of the plantar-foot skin were evaluated using F = kX + cX̍. Three indentation speeds (1 mm/s, 3 mm/s and 5 mm/s) were used to determine the mechanical properties of five different locations in the plantar-foot in East Asian and South Asian participants. The model F = kX + cX̍ fits the experimental data with a relatively high coefficient of determination (R² > 0.84) for each subject and each testing location. Both, the testing location and the ethnic groups showed significant effects on the 'k' and the 'c' values.

Indentation area dependency on 'k' and 'c' values were evaluated in another experiment with twenty-four South Asian participants using three different indentation areas at five different testing locations in the plantar-foot. The indentation area and the testing location showed significant effects on k' and 'c' values. Plantar-foot skin deformation can be modeled in the form of F = (j (A) + k)) X + (m (A) + n) X̍.; where j, k, m, n are constants at each testing location.

The results can be used to develop new designs for footbeds considering gender and ethnic group differences.