backwards and forwards

in both directions alternately; to and fro

来来回回

he paced backwards and forwards nervously.

他紧张地来回踱步。

bend (或 fall 或 lean) over backwards

(informal)make every effort to achieve something, especially to be fair or helpful

(非正式)竭尽全力（尤指为实现公平或给予帮助）

we have bent over backwards to ensure a fair trial for the defendants.

我们竭尽全力保证对被告公平审判。

know something backwards

be entirely familiar with something

了如指掌