A hyperelastic constitutive law, for use in anatomically accurate finite element models of
living structures, is suggested for the passive and the active mechanical properties of incompressible
biological tissues. This law considers the passive and active states as a same hyperelastic continuum
medium, and uses an activation function in order to describe the whole contraction phase.
The variational and the FE formulations are also presented, and the FE code has been validated
and applied to describe the biomechanical behavior of a thick-walled anisotropic cylinder under
different active loading conditions.