Crossunder?
Ah, I did wonder if you were meaning backward runs/progressives but the forwards direction scotched that! Still not quite sure I'm with you but I think you mean the push given by the inside leg in crossovers...?
A coach showed it to us once. She was a whizz at it. Over 50 and still burning up the ice, outrunning the youngsters, perfectly extended free leg, great upper body posture...