This is a really tough exercise for me. I can’t do it yet like the person modeling it. I’m guessing fake it til I make it will work? Maybe just get good at extension before moving my extremities will be a baby step. 

James  Some of the challenge is also hip flexors, and open shoulders.   Extension of the spine is also a factor, yes, just practice but watch if you are uncomfortable in your lower back.  Maybe practice lifting your limbs, wiht your head down so see if you can even lift Right arm, left let, etc.   That is a good start, and ofcourse, practice.   Great question!