What is it and What Does it Feel Like? The term tendonitis refers to acute inflammation of the tissue and tendinosis is a chronic inflammation and thickening of the tendon resulting in degeneration over time. These conditions are both characterized by pain, inflammation, stiffness and limited tolerance to activity.  What Causes the Pain? The pain in both these conditions is a result of altered mechanics over time, repetitive stress as well as intrinsic factors in the body.  Diagnostic Testing It is important to obtain diagnostic testing prior to treatment of achilles conditions. Bony calcificatons, blood flow, and degree of thickening of tissue can be determined with imaging studies and ultrasound.  …