Muscle fibres have a complex hierarchical internal structure which leads to a marked decrease in the observed MR diffusion coefficient with diffusion time. We expect the form of this diffusion time dependence to be highly sensitive to changes in this internal structure. However, characterising the diffusion time dependence in tissue can be highly demanding of total acquisition time. We examine the time-dependence of diffusion indices in human calf muscle in healthy volunteers in a clinically feasible scan time. We find significant time dependence and diffusion restriction in all directions, including longitudinally, due to the internal structure of muscle fibres.