Thanks for you comments.

Part of the concern is how athletes are making best usage of their
calf muscles, which are quite powerful muscles, as experienced in
running.

Calf muscle usage is obvious during "jump" skate, but what about other
technique ?

At the end of the side push, their is a little time for best using
them, I think.
But at the end of the push, the legs is rather backward. The more you
step forward, the more backward is the pushing leg.
I noticed that Northug (unfortunately not in my video) does
"something" at the end of his pushes with his foot/calf, as seen when
how the tip of his ski returns. I'll try to compile or find another
video depicting that.