The goal of this observational study is to test whether a new ultrasound method, called SUper Resolution ultrasound imaging of Erythrocytes (SURE), can image the small blood vessels found in tendons of persons with a tendon overuse injury (tendinopathy). The main questions it aims to answer are: * Is the method sensitive enough to detect the smallest blood vessels * What information about the blood flow can be obtained (flow velocity, pressure, shape of the vessels) * Can the flow in an injured tendon be distinguished from that of a healthy one Participants will receive a non-invasive ultrasound examination of their Achilles (heel) or patellar (knee) tendon, using an advanced high frequency research ultrasound system. Researchers will compare participants with either an Achilles or patellar tendon overuse injury to participants with healthy tendons, to see if there are distinct differences in the blood vessels that could help diagnose and treat the injuries.