Footbed effects on perceived sensations and predictive models of footwear fit
by Channa Patuwatha Witana
Ph.D. Industrial Engineering and Logistics Management
xxxii, 282 leaves : ill. (some col.) ; 30 cm
The interaction between the loaded foot and the footbed is critical for footwear fit and comfort. Previous studies have shown that altering plantar pressure distributions can affect comfort. Hence a good fitting footbed is important for improving footwear comfort. The focus of this thesis was to investigate the necessary shape for the footbed in order to improve comfort for any foot shape....[ Read more ]
The interaction between the loaded foot and the footbed is critical for footwear fit and comfort. Previous studies have shown that altering plantar pressure distributions can affect comfort. Hence a good fitting footbed is important for improving footwear comfort. The focus of this thesis was to investigate the necessary shape for the footbed in order to improve comfort for any foot shape.
The perceived footwear fit in midfoot and forefoot in medio-lateral sides was highly correlated with the dimensional differences between foot and shoe-last in the corresponding regions. A fit that is neither tight nor loose can be achieved when the dimensional difference is around 8 mm on the width at toe region and around 15mm on the midfoot width.
In order to study various footbed shapes, a novel mechanical device was invented. The device was able to vary heel height, heel wedge angle, heel seat, shank shape, arch length and toe spring. The footbed shape deformations were estimated using structural bending theories where the largest estimation error found was 3.70mm at the midfoot region. Thereafter, the effects of footbed shapes on the plantar foot shape were studied in detail since the changes in foot shape have to be accounted for when designing shoes. It was found that the structure of the midfoot can change independently thereby creating changes in its plantar shape. The participants taking part in the experiment were able to judge these shape changes in the midfoot region and showed different preferences for different midfoot shapes.
Knowing the characteristics of midfoot deformation, various footbed shapes were studied at different heel heights to understand their relation to perceived footwear comfort. It was found that there exists a unique footbed surface shape for the foot to feel comfortable at each tested heel height. In order to obtain such a footbed shape there are three conditions that have to be satisfied simultaneously: the contact area has to be higher than that of when standing on a flat surface, the peak pressure has to be lower than approximately 100 kPa and the percentage of force acting on the forefoot has to be approximately within 15 % to 22.5% of the total force. Prediction models (i.e. for each heel height) were proposed and validated based on the comfortable footbed shapes to predict the required footbed shape for given basic foot dimensions. An algorithm was proposed to transform an unconstrained 3D foot shape (when standing on floor) in to a shape where the foot is supported on a comfortable footbed shape. The accuracy of the above mentioned 3D foot modeling algorithm was within ± 1.02 cm.
The findings from this thesis, including the footbed prediction models and the invented device, have the potential to be integrated into footwear design, thus improving footwear comfort.