It’s a common injury among runners and other athletes, and now researchers say they know exactly what causes the painful and often debilitating condition known as runner’s knee.

Research done at the University of North Carolina at Chapel Hill and published in the November issue of the American Journal of Sports Medicine found that there are several causes of the condition formally known as patellofemoral pain syndrome.

Scientists say the pain associated with the condition can be explained by a number of different factors coming together to create a focal point of pressure between the kneecap and the underlying bone. These factors include weaker hamstring and quadricep muscles, a smaller knee flexion angle and a larger navicular drop in the arch of the foot.

The study is believed to be the first long-term research looking at issues of strength and biomechanics that could affect the condition before it occurs.

Patellofemoral pain syndrome affects about one out of every four athletes. "It can be devastating. The pain can severely curtail a person’s ability to exercise and the symptoms commonly reoccur," said the study’s co-author Dr Darin Padua.

He also says the good news is that the study appears to confirm that if people can change the way they move and improve their leg strength, they can prevent or correct the problem.

Other common treatments for runner’s knee include icing the knee after activity and wearing proper, supportive footwear, according to CoolRunning.com.