Motor unit (MU) magnetic resonance imaging (MUMRI) is a non-invasive technique which detects muscle fibre micro-contraction and is based on diffusion weighted MRI. To date MUMRI has been applied in conjunction with in scanner electrical stimulation to study MU activity in the lower leg. Here we present the first use of MUMRI in the upper limbs to study single human MUs. The acquired images show low levels of distortion and good fat suppression, allowing single human MU sizes and shapes to be determined. This is of interest in neuromuscular diseases as it is a non-invasive way to study MU morphology.