Motor units (MUs) play a fundamental role in muscle physiology and disease. They can be imaged using a diffusion weighted imaging technique, motor unit MRI (MUMRI). Previous work activated MUs using electrical stimulation, limiting MUMRI to muscles innervated from superficial nerves. Here, we demonstrated the feasibility of MUMRI during volitional muscle activation. We confirmed that the MU activity detected with MUMRI during muscle contraction increased with b-value, force level and was dependent on the diffusion-sensitisation direction. This work allows us to image MUs in situations reflecting real muscle physiology making it a promising tool for studying motor neuron diseases.