To finally get moving or take action after reluctance or delaying; to rouse oneself to do something one has been putting off.
週末にやっと重い腰を上げて部屋の掃除をした。
I finally got off my backside and cleaned the room over the weekend.
彼はずっと先延ばしにしていた書類作成に、ようやく重い腰を上げた。
He at last mustered the energy to start the paperwork he'd been postponing.
先生が声をかけたおかげで、クラス全員が重い腰を上げて準備を始めた。
Thanks to the teacher's prompting, the whole class finally got moving and started preparing.