Bend Over Backwards

[Shatnerfan]

Why is 'Bending Over Backwards' a phrase for being extremely helpful?

[Quizmonster]

As Tartanwizard says, there is always an element of inconvenience there. Also, there is often the idea of going to the opposite extreme in order to avoid any suggestion of bias...sometimes even one that you are going almost too far in an effort to overcome your natural 'inclination' perhaps NOT to help. The phrase first appeared in the 1920s.