A method is proposed for myocardial strain estimation, based on 3D isotropic cine MRI. A free-breathing, motion-corrected super-resolution acquisition is used to obtain the 3D isotropic cine dataset. Then the left ventricular (LV) myocardium is manually segmented using a sparse segmentation technique. Finally a registration-based technique is used to obtain displacement fields that best match diastolic and systolic 3D isotropic masks of the LV, and subsequent Lagrangian strain estimates. The method was evaluated in 20 Duchenne muscular dystrophy patients. Segment-wise analysis showed that the proposed radial strain estimates correlated well with the presence of fibrosis.