While taking their usual bath, the boys discuss how much Kyotaro is like an old man. The next day, when they go to school, they find themselves exhausted by climbing up the stairs... and learn that they're all becoming old men!
The change in temperature puts a strain 
on the body, particularly the heart.
يشكّل التغيّر في درجة الحرارة جهداً على الجسم
ولا سيّما القلب
und das Herz überlastet!
El cambio de temperatura
afecta al corazón.
El cambio de temperatura
afecta al corazón.
subit un choc thermique
qu’il supporte mal.
Il cambio di temperatura stressa il corpo,
in particolare il cuore.
A mudança de temperatura cria uma tensão
no corpo deles, principalmente no coração.
Всё это создаёт нагрузку на сердце.