Btw, I'm kind of surprised what does the weight of "баба" have to do with the activity of breaking the eggshell?
Beside breaking eggshells a typical "баба" was supposed to stop a horse on the run, enter the house on fire,… make buns, after all. You can make sure yourself how true that might have been. Just take a look at the “volumes” of the peasant’s spouse on the video below ... well it’s simply the result of the natural selection, survival of the fittest, the byproduct of the evolution of species, etc…

http://www.youtube.com/watch?v=6DfDcqYCwis