An idiomatic expression meaning that something is hard to do, requires a lot of effort, or is laborious; to be troublesome or demanding.
このプロジェクトは調整が多くて本当に骨が折れる。
This project requires a lot of coordination and is really hard work.
彼のために書類をそろえるのは骨が折れたが、喜んでもらえた。
It was a lot of trouble to gather the documents for him, but he was pleased.
新入社員の教育は時間も気力もかかり、骨が折れる仕事だ。
Training new employees takes time and energy; it's a demanding task.