Viscoelasticity in Foot-Ground Interaction

Abstract

Mechanical properties of the plantar soft tissue, which acts as the interface between the skeleton and the ground, play an important role in distributing the force underneath the foot and in influencing the load transfer to the entire body during weight-bearing activities. Hence, understanding the mechanical behaviour of the plantar soft tissue and the mathematical equations that govern such behaviour can have important applications in investigating the effect of disease and injuries on soft tissue function. The plantar soft tissue of the foot shows a viscoelastic behaviour, where the reaction force is not only dependent on the amount of deformation but also influenced by the deformation rate. This chapter provides an insight into the mechanical behaviour of plantar soft tissue during loading with specific emphasis on heel pad, which is the first point of contact during normal gait. Furthermore, the methods of assessing the mechanical behaviour including the in vitro/in situ and in vivo are discussed, and examples of creep, stress relaxation, rate dependency and hysteresis behaviour of the heel pad are shown. In addition, the viscoelastic models that represent the mechanical behaviour of the plantar soft tissue under load along with the equations that govern this behaviour are elaborated and discussed.

Can plantar soft tissue mechanics enhance prognosis of diabetic foot ulcer?

“…This is also indirectly supported by the 121 reported significantly higher heel pad stiffness in people with 122 higher levels of Fasting Blood Sugar [24]. in the clinic [25]. This study by Naemi and co-workers [25] 146 indicated that compared to non-ulcerated group, the ulcer-147 ated group had a significantly lower heel pad stiffness [25].…”

“…in the clinic [25]. This study by Naemi and co-workers [25] 146 indicated that compared to non-ulcerated group, the ulcer-147 ated group had a significantly lower heel pad stiffness [25]. Table 2 shows the categorical parameters including sex, smoking, Oral Hypoglycaemic Agent (OHA) use, insulin only use, OHA & insulin use, history of eye surgery, Edema/swollen feet, tineapedic, onychomycosis, callus, history of ulcer, history of callus and foot shape abnormality for the participants and also for each group.…”

Diabetes Status is Associated With Plantar Soft Tissue Stiffness Measured Using Ultrasound Reverberant Shear Wave Elastography Approach

“…The plantar soft tissue of the foot consists of highly specialized tissues which present with complex nonlinear, visco-elastic mechanical properties in addition to a complex internal structure comprising of both skin and plantar fat pad [1].…”

“…The plantar soft tissue of the foot consists of highly specialized tissues that present with complex nonlinear, viscoelastic mechanical properties in addition to a complex internal structure comprising of both skin and plantar fat pad. 1 Previous studies show that diabetes is associated with changes in the plantar soft tissue mechanical properties as a result of glycation which is associated with an increased blood sugar level over prolonged periods of time. Specifically, the plantar soft tissue in people with diabetes compared with the age-matched groups of people without diabetes is thicker, 2 stiffer, 3,4 harder 5 , and also tends to have less energy return efficiency.…”

The Effects of Walking Speed and Hardness of Terrain on the Foot-Terrain Interaction and Driving Torque for Planar Human Walking

“…However, the effect of soft tissue deformation is so small that can be neglect compared with that of terrain deformation in the off-road walking occasions. More practically, soft issues at heel pads interacting with rigid ground were often described by non-linear viscoelastic models [32]. The linkages among heel, phalangeal joint, and toe (can be approximated by three spheres [33]) will add viscosity and response delay for the total system.…”