Why does patellar tendinitis cause knee pain?

The patellar tendon transfers force from the thigh muscles through the kneecap to the lower leg. Running, jumping, repeated squats, or a sudden increase in training can place more load on it than it can comfortably manage. The tendon may become painful and less tolerant of pressure. Symptoms are often felt just below the kneecap and may be sharper during jumping, stairs, or rising from a chair. Pain that persists at rest, follows a major injury, or is accompanied by marked weakness needs a broader assessment.

Temporarily reduce activities that provoke pain, especially repeated jumping and deep knee bending, while keeping gentle movement within comfort. Ice wrapped in cloth can help after activity. A physiotherapist can guide gradual strengthening of the thigh, hip, and tendon; increasing load too quickly can bring symptoms back. Return to sport or heavy work in stages, using pain and next-day response as useful feedback rather than pushing through a sharp increase.

Arrange an assessment if pain is worsening, limits ordinary walking, or has not improved after reducing aggravating activity. Seek urgent care after a sudden tear-like event if the knee gives way or you cannot actively straighten it. Rapid swelling, redness with fever, or a hot joint also needs prompt evaluation.

Ask which activities are safe now, how to progress tendon loading, and whether your training technique or footwear may be contributing. Find out what improvement should look like and when persistent pain would justify imaging or another diagnosis.