Neuromuscular diseases can lead to characteristic changes in the anatomy of motor units (MU). In this study we developed an MR approach to image motor unit activity. In-scanner electrical stimulation of MU was synchronized to a pulsed-gradient spin-echo imaging sequence sensitive to microscopic contraction of muscle fibers. Experimental data was compared to a simple theoretical model and scan parameters evaluated. The spatial pattern of muscle fibers forming different MU was imaged for the first time in healthy controls.