1
general::
Phrase(s): bend over backwards (to do something)
Go to fall over backwards (to do something)., Phrase(s): bend over backwards (to do something) (for someone)
Fig. to work very hard to accomplish something for someone; to go out of one’s way (to do something) (for someone). (See also fall over backwards (to do something).) • He will bend over backwards to help you. • I bent over backwards for you, and you showed no thanks!
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Also, lean over backwards. Exert oneself to the fullest extent, as in Dad bent over backwards so as not to embarrass Stasia's new boyfriend. This phrase transfers the gymnastic feat of a backbend to taking a great deal of trouble for someone or something. [c. 1920] Also see under FALL ALL OVER.
American Heritage Idioms