Tendons are the tough, fibrous cords that connect muscle to bone. Tendinitis is inflammation of a tendon. Injury, overexertion, infection and, occasionally, other diseases can cause inflammation. But most of the time, it's caused by too much stretching of the tendons. The condition is characterized by pain when touched or moved, and limited range of motion and movement.
Tendinitis occurs more often as one gets older.
However, it is also relatively common in young people who exercise vigorously or perform repetitive physical tasks. Certain tendons are more susceptible to inflammation than others. Tendons in hands and arms are especially at risk. Some tendons are covered by tendon sheaths. Normal tendons slide easily in and out of the surrounding sheaths.