Patellar tendinopathy, also known as jumper's knee, is a chronic overuse injury caused by repetitive stress on the knee extensor mechanism from activities like jumping, running, and kicking. It results from microtears in the patellar tendon from forces that are 3 times greater than normal during movements like acceleration, deceleration, takeoff, and landing. Symptoms include dull aching knee pain after exercise that worsens with sitting or stairs. Treatment focuses on eccentric strengthening exercises and bracing to promote healing of the tendon.