They are the two most common injuries. Tendonitis is an inflammatory response of tendon tissue accompanied by redness, swelling, fever, and pain, which is a stress response of the body’s immune system after detecting inflammation. Tendon degeneration is a degenerative change in tendon tissue and does not cause an immune response. The tendon tissue is subjected to repetitive strain over a long period of time and the collagen fibers are damaged and degenerate, making the tendon weak and less tense.