Tendonitis refers to a type of sterile inflammation that occurs in the tendons and surrounding tissues due to various reasons. Its formation typically follows these four causes: First, acute injury, which usually occurs after the tendons are impacted violently, causing tears or ruptures and leading to an inflammatory reaction in the tendon and surrounding area. Second, long-term wear and tear. This is primarily seen in tendons that are repeatedly subjected to abnormal, unhealthy wear and tear, leading to increased tendon burden or instability at the attachment points, which then causes a surrounding inflammatory response. Third, increased tendon load, leading to damage in the tendon itself, and even causing tears and bleeding, forming a reactive inflammation. The final cause is due to excessively long exercise periods or overloading the tendons through exercise, causing tendon congestion and edema, and eventually leading to inflammation. This can occur in individuals who suddenly engage in heavy exercise after a period of inactivity, or athletes who train daily for extended periods without adequate rest, causing the tendons to be under constant stress. Over time, like a bowstring, this can lead to slackening or rupture, causing an inflammatory response around the tendon or in the tendon itself. Thus, tendonitis generally arises from the reasons mentioned above, often seen in chronic strain and improper posture during exercise, and less commonly from acute injuries and increased loads.