The hip flexors are a group of muscles in the hip joint that move the hip and by extension the leg forward while running or walking. The hip flexors also work with the abdominal muscles and work when the stomach is moved toward the legs, as in sit-ups. Hip flexor stretches can help improve general back health. Learn how to stretch the hip flexors from a chiropractor in this free back health video. Learn also what are the hip flexor strain treatment.