Those two mincers on "Myth-Busters" did a busting session on the brace position. They got some wallahs to sit in a mock-up and assume the position before the entire arrangement was dropped from a height onto the ground.
When the dust had settled it emerged that they slightly less intense permanent back difficulties if they used the position.
As a long-term sceptic, I was moved.
The real question is, if they can make the black box (aka flight data recorder) out of light-weight indestructible materials, why not make the entire aircraft that way?