Hip Flexor Stretch - Video
This stretch is typically performed by resting the toes on a chair or some steps. Alternatively, if this is too hard to do, it can be performed by simply drawing the leg back so the toes are in contact with the floor. Once in this position the steps are:
(1) Straighten the back knee out.
(2) Make sure you're standing upright.
(3) Clench your buttocks.