Bend over backwards
(PW) try very hard
He’ll bend over backwards to help any of his friends.
(MW) bend over backward or bend over backwards : to make extreme efforts
(yourdicitionary)
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.
(freedictionary) 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). He will bend over backwards to help you. I bent over backwards for you, and you showed no thanks!
bend/lean over backwards to do something (British, American & Australian) also fall over backwards to do something (Australian)
to try very hard to do something, especially to help or please someone else Banks are bending over backwards to help those in difficulties.
(urbandictionary)make a very big effort
My sister bends over backwards to help the doctor check her temperature
(thePhraseFinder)
If you bend over backwards for someone, you're going out of your way to do make an extra effort to do something for someone.
Clearly bending over backwards is doing something extraordinary (hell knows it's a huge physical effort to me - I can't bend over backwards very far) - but it's also a very strange thing to say or do. Does anyone know when and why anyone would dream up such a contortion to describe an extraordinary deed?
(goEnglish) inconvenience yourself to help another ...
You bend over backwards when you put yourself in an uncomfortable position in order to help another person. Example: "We bent over backwards to help him, and he never even thanked us!"
It is difficult to bend over backwards, and it feels awkward, but you are willing to do it to help certain people. Example: "My dad knows that I would bend over backwards to help him if he needed it."
At other times you are only willing to help when it is convenient for you, and you would not bend over backwards. Example: "I will help you out if you need it, but I am not bending over backwards for you."