Getting a good psoas stretch is necessary in order to get its opposing muscle, the glutes (your butt muscles) to activate.
The key to doing this lies in performing a posterior pelvic tilt. When you split your stance so that one leg is quite a bit behind your body, then squeeze your butt muscles, and bring the front of your pelvis up toward your chest, you'll feel the psoas stretch very strongly.
Hold for 20-30 seconds, for 1-3 reps on each side.
Sam Visnic--
