  The Finite Element Method (FEM) is a well-established procedure for computing
approximate solutions to deterministic engineering problems described by
partial differential equations. FEM produces discrete approximations of the
solution with a discretisation error that can be an be quantified with \emph{a
posteriori} error estimates. The practical relevance of error estimates for
biomechanics problems, especially for soft tissue where the response is
governed by large strains, is rarely addressed. In this contribution, we
propose an implementation of \emph{a posteriori} error estimates targeting a
user-defined quantity of interest, using the Dual Weighted Residual (DWR)
technique tailored to biomechanics. The proposed method considers a general
setting that encompasses three-dimensional geometries and model
non-linearities, which appear in hyperelastic soft tissues. We take advantage
of the automatic differentiation capabilities embedded in modern finite element
software, which allows the error estimates to be computed generically for a
large class of models and constitutive laws. First we validate our methodology
using experimental measurements from silicone samples, and then illustrate its
applicability for patient-specific computations of pressure ulcers on a human
heel.
