彼は子供の頃から病弱で、学校を休みがちだった。
He has been sickly since childhood and often missed school.
病弱な母の代わりに、姉が家事を引き受けていた。
My older sister took on the housework in place of our frail mother.
病弱を理由に、彼は兵役を免除された。
He was exempted from military service on the grounds of poor health.