It incorporates the piriformis as well as the gemellus superior and inferior. The obturatus internus and externus are involved along with the quadratus femoris, which all work together in the rotation of the femur joining to the pelvis.
Don't ever under estimate the importance of stretching and the benefits it holds.
The Standing leg tuck hip stretch is useful in helping with sporting injuries such as piriformis syndrome, snapping hip syndrome and trochanteric bursitis.
Always rememberthat while stretching may be recommended to aid recovery out of injury, you should always be very careful when stretching through rehabilitation. Your soft tissues are likely to be more vulnerable to re-injury if you stretch too much or too hard during this time. Always check with your Health Care Professional who is guiding you through your recovery to make sure it is appropriate to start stretching, and please - ALWAYS FOLLOW THE RULES FOR SAFE STRETCHING (The first posting on this stretching blog).
Image taken from "Lower Body Stretches" wall chart by B. Walker.