The iliotibial band is a thick band of fibrous tissue that runs down the outside of your leg and helps provide stability to the outside of the knee joint. IT band syndrome is when this band becomes inflamed.
Moving your knee becomes painful; it worsens with continued movement, and it resolves with rest.
The cause is usually a sudden increase in activity. Runners who increase their mileage too fast often develop iliotibial band syndrome, as do individuals with biomechanical problems with their gait such overpronation, leg length discrepancies, or individuals who are bow-legged, or those who have dominant pelvic rotation.