Beginner question on hollow body.

[Guest Esa Lackström 173096]

Should i keep the natural curve of my spine on this exercise?

I have understood this that i should press my lower back to floor completely, and after i while i start to shake visibly. I can still hold the position, i can breathe and talk. My core just shakes uncontrollably. 

[Alessandro Mainente 10,593]

It is a natural sign of weak core, if the spine it is held in a neutral position why we should call it "hollow"?