head down, bum up

Etymology
From an assumed position of strenuous work. Compare.

Adverb

 * 1)  Hard at work; preparing oneself to work hard.
 * 2) * 2007 April 6,, "Call of Sea Sirens":
 * Hadn't heard a thing. Hard at work, head down, bum up.

Usage notes
Not to be confused with the American forms /,  in reference to being a position to be sexually exploited. Similarly, neither is equivalent to, meaning to avoid notice.