This five and a half minute movie is to help you isolate your Psoas and over-ride the instinct to use your Abdominals and Quadratus Lumborum to hold your posture.
I need to point out that Brian had his arms high to be out of the movie...which pinched his Scapula and splayed his ribs. A better way to do this exercise is with your ribs relaxed on the floor.
With that said:
It is very difficult to have a neutral pelvis. The best way to find out if your pelvis is neutral is to mark on the front of your hip (the Anterior Superior Illiac Spine) and the back of your hip (the Posterior Superior Illiac Spine). Then use a straight stick/ruler/level to show if your two Illiac spines are level with each other OR spilling one way or another.
After personal dance accidents and uneducated instructors I recovered from an anterior pelvic tilt only to fall into a posterior pelvic tilt. These exercises, done for two years, have created an equilibrium. I now enjoy a neutral pelvis and less Lumbar pain.
Begin: (Always check with your doctor to make sure your personal body ailments can withstand new exercises. If you're poor? Avoid sharp or needle-like pain. No pain? You gain.)
Start by laying on the ground with your arms to your sides. Raise your knees (like those old fashioned sit-ups) with your feet hip width apart. Check to make sure your back is spread on the floor and your lower ribs are pressing into the floor as well (not raising to the sky).
Now rock your hips back and forth. Anterior, Neutral, Posterior, Neutral, Anterior, etc. Try to keeps your ribs down while doing this.
If this causes pain? STOP! Go to a Chiropractor or Sports Therapist. They have the technology to take X-rays and see what your personal ailment includes. (Sorry to all those doctors...I never had much help from you in this regard.)
From neutral press your lower back into the ground (posterior pelvic tilt). Lengthen the angle from your hip to your thigh. slowly roll up to a plank position. Do this one vertebrae at a time. You can use the image of your hips trying to reach the top and your ribs being too comfortable with the floor to comply easily.
When your reach the plank or diagonal hold it there for a few seconds. Make sure that your back is not curved to the sky. If it is you went too far. Your body should be flat like a board.
As you roll down try to leave your hips in the air as long as possible. Your ribs will start and try to reach the floor first.
Stretching? Watch the movie for some lower lumbar stretches. Another, not included, is to sit and stretch your body directly to the side. Do it in both directions.
Be gentle. Be careful. Repetitions. Patience.