Hi Zoe! Tendon injuries can be very frustrating!
The damage of tendon tissue is characterized by inflammation, with the hallmarks of inflammation in any tissue being the presence of heat, pain, and swelling. It is therefore appropriate to call most tendon injuries a tendonitis.
It is commonly agreed upon that tendonitis results from excessive stress on the tendon that stretches and ruptures the tendon fiber bundles. most cases of tendonitis are thought to result from an "additive" effect of previous and repetitive low-grade tendon fiber disruptions. With each repetitive stress, there is minor disruption or tearing of the tendon fibers.
This damage causes some degree of inflammation in the area and causes edema (collection of fluid) within and around the tendon as well as the production of inflammatory enzymes that further damage the collagen fibers of the tendon. The net result of the inflammation created by the tendon fiber tearing is a series of events that further damage and weaken the surrounding tendon fibers.