The iliotibial band is a thickening of the fascia lata, the deep fascia of the thigh. Think of it as a thick long ligament like structure that connects the hip to the lower leg along the outside of the thigh. Tightness in the iliotibial band can cause patellofemoral pain, trochanteric bursitis, and friction syndromes at the knee. This is a hip stretch I commonly prescribe to runners and people suffering from knee pain.
A sedentary lifestyle can lead to having weak and tight hip flexors as they are always in the shortened position. Tight hip flexors can lead to a limited range of motion, poor posture, lower back and hip pain, and even injuries. These muscles need to get a workout when you are standing and doing movements such as raising your leg to climb stairs, run, or ride a bicycle.