Idiom: "(to) knock oneself out"

Definition:

to work very hard at something (sometimes too hard)

Examples:

1) Larry knocked himself out trying to study for his GREs.

2) Don’t knock yourself out trying to help Sam.  He won’t appreciate it anyway.

中文解释：http://www.youzienglish.com/main/idiom_of_the_day/to_knock_oneself_out/cn/