Motor units are fundamental components in the process of contraction of skeletal muscle. Motor unit morphology changes in response to pathologies including motor neurone disease and sarcopenia. Currently the clinical method to investigate motor unit morphology and activity is invasive needle electromyography. Here we present a novel diffusion weighted imaging technique, motor unit MRI (MUMRI). MUMRI has been used to investigate the morphology of single human motor units, producing quantitative data on cross sectional area and dimensions of human motor units. This data agrees with current literature. MUMRI has detected statistically significant changes in the morphology of motor units.