From anatomical and histological observations, the plantar aponeurosis tissue  appears to be made up of a ground matrix and reinforced by collagen fibers that are mainly oriented along the proximal-distal direction.
These constitutive parameters are obtained by a fitting procedure of the hyperelastic model to experimental data of the plantar aponeurosis elastic response, taken from the literature [5,13].
In fact, it is possible to observe that the model well fits both average data from tests at different levels of strain applied (Figure 2) and global average data from the two different plantar aponeurosis mentioned above (Figure 4).
As expected, according it viscoelastic properties, the plantar aponeurosis tissue exhibits an increasing stiffness concurrently with the strain rate increase.
The limits of the present work must be considered in order to evaluate its significance and to plan further investigation on the mechanics of the plantar aponeurosis.
The analysis of the viscoelastic behavior of the plantar aponeurosis along the medial-lateral direction could require distinguishing between viscous behavior of ground matrix and fibers that in this work are not considered.
The study could comprise the evaluation of the viscoelastic phenomena in plantar aponeurosis of younger subjects and, if need be, how these phenomena could differ from those reported in the present work where donors were over 65 years of age.
The investigation is mainly addressed to viscous phenomena of the plantar aponeurosis according to different samples and placement of the samples.
The main purpose of defining this constitutive model for the plantar aponeurosis is the adoption of this model for investigating foot biomechanics using a numerical approach.
The ESWT content The moment of Number of Area on which the shocks were applied application applied of the ESWT shocks Monday 4000 Calcaneal plantar side, aponeurosis insertion, plantar aponeurosis
Thursday 4000 Calcaneal plantar side, aponeurosis insertion, plantar aponeurosis