Tendinitis is the inflammation of the tendon and results from microtears occuring when the musculotendinous unit is acutely overloaded with a tensile force that supercedes the capacity of the tendon.  Tendinitis is a very common diagnosis, although was is thought to be tendinitis is most likely usually tendinosis.

Tendinosis is what occurs with frequent/unaddressed tendinitis.  It is a degeneration of the tendon’s collagen in response to chronic overuse without proper healing of the tendon.