The foot–ground or foot–footwear interface is important as all body weight acts on the area of contact. Foot deformities, ulcers, corns, calluses and bunions are generally caused by excessive pressure and/or friction mainly due to improper design of footwear.
Pressure on the foot depends on factors such as body weight, type of activity performed and the type of footwear worn. Excessive pressure will make people experience discomfort or even pain and can cause leg fatigue and overall stress with a reduction in people’s efficiency and productivity. Many researchers and practitioners have investigated and attempted to increase the area of contact, thereby reducing pressure, through various means to reduce discomfort and pain and possibly increase comfort.
The optimal force distribution to minimise pain or discomfort at the foot–shoe interface is still not known. Most shoe related products attempt to distribute the load uniformly without much consideration to the bony and soft tissue regions.
The authors did an experiment to first determine the pressure pain threshold (PPT) and tissue deformation on the plantar surface of the foot. Circular probes of areas 0.5, 1.0 and 2.0 cm2 at indentation speeds of 0.5, 1 and 2 mm/s showed that PPT depends on the location stimulated, area of stimulation and the indentation speed. The results also showed that tissue stiffness is quite low for small deformations (,4 mm), but significantly higher at large deformations (.4 mm).
The data were further used to develop a model with PPT, deformation and stimulated area.
The authors concluded that manipulating supporting surface stiffness and surface contours can help minimise pain.