Fig. 4. (A) Transverse slab S through the muscle tissue (red), for one side of the body. Medial plane (dark blue) is straight (reference configuration). Global coordinate system (x, y, z) is indicated. (B) Similar to A, but with curved medial plane. (C) Muscle portion from the slab of A₀, infinitesimal fibre element in red; area A₀ is shown in green. (D) Similar to C, but with curved medial plane and added shear deformation. (E) Projection of the muscle portion of C onto a horizontal plane with y constant. Projection of muscle fibre segment is shown by red line. (F) Similar to E, but with added shear deformation and curved medial plane. Local Cartesian system (x', y', z') has its origin (0,0,0) in the centre of curvature. The x'-axis and the z'-axis are shown as broken lines. For further explanations, see main text.