Why do my knee caps hurt when I run, squat or descend stairs?

The causes for pain behind the knee cap can be coming from any number of problems or multiple issues combined. Getting your legs assessed by a trained movement assessment specialist for possible faulty alignment issues in the leg joints,insufficient muscle strength, sport training errors, and overly tight muscles is a good start. As the knee cap is often overstressed and thus giving you a pain message to change your movement or sport training.