The hip flexors are the muscles that cross the front of the hip, including the quadriceps and the iliopsoas. They bring the thigh up for activities such as going up stairs or running. Tight hip flexors are quite common, especially amongst those who spend the majority of their time seated. When these muscles are tight, it can affect the alignment of the pelvis, which connects with the lower back and hip. Having strong and mobile hip flexors can help improve posture, reduce hip and low back pain, and improve efficiency of movement.