Healthcare providers usually call pain at the front of your knee or under your kneecap patellofemoral pain syndrome. Most often, this pain occurs after exercise, but you may also feel it if you sit too long. Over time, your knee may begin to hurt during exercise or throughout the day. You may feel a nagging ache or an occasional sharp pain. This pain may cause you to limp and may limit your activities. Read full article (PDF) 
Perspectives for Patients – Knee Pain from the Journal of Orthopaedic & Sports Physical Therapy
