プログレッシブ和英中辞典(第4版)の解説
あしこし【足腰】
年を取ると足腰が弱くなる
As we get older, our legs [leg muscles] weaken.
足腰が立たなくなる
become unable to stand
足腰が立つうちは働きたい
I want to work as long as I'm able (to get around).
足腰が立たなくなるほど痛めつける
beat a person until he can no longer stand