>11. Medial and lateral longitudinal arch height have very significant effect on MTJ sagittal plane stiffness due to engineering principle that states that stiffness of a material is directly related to the cross-sectional thickness of that material.
>This statement mixes two engineering principles and some clarification may be helpful to lessen any potential misconceptions.
1. The cross-sectional thickness of a material is proportional to its stiffness.
2. MLA and LLA heights are shape functions, however, not thickness functions. Shape exerts a large influence on stiffness.
As an example - corrugated iron is more resistant to bending, in certain planes, than a flat sheet of steel (even though both sheets have a uniform thickness).
Feet with arches will be more resistant to bending (particularly in the sag plane) than "flat" feet - assuming similar dimensions and that the joints remain appropriately stable.
Elegant engineering designs generally tend towards the minimum of material, but achieve the desired stiffness by virtue of their "shape". Feet are not linear blocks, but elegantly shaped structures.
If you really want to master this subject, and have nothing better to do with your spare time, try, Benham & Warnock, "Mechanics of Solids and Structures". ;-)
Regards,
Stephen
Stephen Urry PhD
Lecturer
School of Public Health
Queensland University of Technology
Brisbane
4059
Australia
CRICOS No 00213J
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