Input geometry for CA. Blue dots represent muscle tissue, green dots correspond to the conducting system, where the excitation propagation speed is much higher.

All simulations used the same FE mesh. Due to symmetry, only one half of the ball was used. Two different CA inputs served for the activation computation.

• Case A: 25x50x50 cells, half-sphere (-> border effects), 5 FE step ~ 1 CA step.
• Case B1: 100x100x100 cells, sphere, 5 FE step ~ 1 CA step.
• Case B2: 100x100x100 cells, sphere, 1 FE step = 1 CA step.

It has been observed that the dynamic response of the structure heavily depends on time step relations of both computations since, for the case when several FEM time steps use one CA step, the activation changes can be rather abrupt. The same holds for coarse cell arrays. Just look at case A animation and compare them with those of case B1. The coarser the CA cell array, the higher is the propagation speed relative to the structure size and hence the activation changes in case A are faster than in case B1. Case B2 was a special run where the step mapping was one to one. However the mesh movements are very small in this case, because the wave propagated too fast to overcome inertial effects.

The material consisted of a hyperelastic matrix, passive viscoelastic (connective) fibres (PF) and active (muscle) fibres (AF), both in two preferential directions (dir1, dir2).