You love to run. Climbing the hills on your usual route used to be a pleasant challenge. Now it hurts to even climb the stairs. What's going on?

Your knees may be telling you that it's time to take a break.

The cartilage under your kneecap (patella) is a natural shock absorber. But it doesn't come with a lifetime guarantee. Overuse, injury or other factors may lead to a condition known as chondromalacia patella — a general term that indicates damage to the cartilage under your kneecap. Chondromalacia patella is more accurately referred to as patellofemoral pain.

The most common symptom of patellofemoral pain is knee pain that increases when you walk up or down stairs. It also may hurt to kneel or squat. Simple treatments — such as rest and ice — often help, but sometimes more aggressive treatment is needed.