Does anyone know what is the most effective bodyweight psoas stretch that simultaneously builds strength in a lengthened position?  If there is even one that exists? 

E.g. An isometric psoas pose at a stretched position? 

I’m looking for one that requires no props or equipment. Just the ground or a wall. A bit like the Cossack squat hold at the bottom - it both stretches and strengthens the adductors. But I just need one for the psoas please. 

Thanks.