Lie on one side. Grasp top ankle or forefoot behind. Pull ankle or forefoot to rear end.
Straighten hip by moving knee backward. Hold stretch. Repeat with opposite side.
During stretch, do not allow knee to flare upward away from floor. If knee is not completely flexed, Iliopsoas wil be stretched more than Quadriceps. Bottom hip and knee can be bent 90° thereby decreasing anterior pelvic tilt so upper leg will not need to be pulled back as far during hip extension. See Lying Tibialis Anterior Stretch for similar exercise which can be combined with this stretch and performed simultaneously.