hena-hena
Describes losing all physical strength — knees buckling, body going limp. Often from shock, relief, or sudden exhaustion.
💡After hearing shocking news — 'My legs went hena-hena and I had to sit down.'
驚きで膝がへなへなになった。
My knees went hena-hena weak from surprise.
After running the marathon, my legs went ___ and I collapsed.
マラソンを走ったあと、足が○○になって倒れた。