Pompe disease is a rare genetic disorder leading to progressive muscle weakness due to a glycogen storage defect, which currently lacks a non-invasive method for early detection and treatment monitoring. This study aims to address this critical need by employing a new MRI technique, Carbon Spectroscopy, which detects the Carbon present in the glycogen of the muscles and therefore allows us to measure glycogen levels in patients with Late-Onset Pompe Disease (LOPD). By tracking changes in muscle glycogen over time there is potential to improve the management of Pompe disease, leading to earlier intervention, improved treatment outcomes, and a better quality of life for patients.