長い入院生活で祖父の足腰がすっかり弱ってしまった。
My grandfather's legs grew very weak during his long stay in hospital.
夏の暑さで体が弱っているから、無理をしないでね。
Your body is worn down from the summer heat, so don't overdo it.
台風は上陸後、次第に勢力が弱ってきた。
After making landfall, the typhoon gradually lost strength.