Skeletal muscles are geometrically complex 3D structures, and cannot be fully characterized by 2D imaging. Therefore, a complete understanding of mechanisms of force transmission and strain development in relation to muscle architecture during contraction requires a 3D approach. We measured strain rate in the lower leg using a 4D accelerated Phase Contrast protocol and 3D muscle architecture with DTI. Our 3D strain rate data revealed a planar pattern, with one negative and one positive strain rate eigenvalue. Strain rate data combined with 3D muscle architecture, suggested a complex and heterogeneous behavior of strain development during muscle contraction.