The more well-toned the pc muscles are, the easier it is to control them, and whatever the muscles are doing will be more effective--whether it's holding pelvic muscles in place, or pushing out a baby.
This logic is discussed in Susan McCucheon's Natural Childbirth the Bradley Way
. I don't own the book, but borrowed it from the library over a year ago--
--and the part of the book that was SO VIVID for me and memorable was the idea that the stronger the pc muscle is, the EASIER it is to control it and use it to push the baby out. Slack, lazy, pathetic muscles will not make it 'easier' to push out the baby, rather, they could be an impedement. Pc muscles are there to be used, not to atrophy. You got it right, kama'aina mama, but I wonder if doing them 'wrong' is really detremental--I would think it'd just be lame or a waste of time, vs. truly harmful.
Honestly, let's think for two minutes about how retarded it is to suggest that a stregthened muscle = an overly tense muscle...do marathon runners have trouble walking 'cause their leg muscles are so strong that their legs are too tense to bend?
I don't know....I know how 'someone said their midwife/OB said Fact X' can carry weight, and I'm glad we're talking about it here, because I really hate it when crapola advice or foolish ideas about birth are perpetuated--we have ENOUGH of that going on in our culture, IMHO.