expression, ichidan verb
be hard (to do); be difficult; require much effort; be laborious
Idiomatic expression literally meaning 'bones break', used to describe a task that is physically or mentally demanding, troublesome, or requires great effort. Often used with a verb in the て-form or a nominalized clause.
この問題を解くのは骨が折れる。
Solving this problem is hard work.
Preparing for the move was really laborious.