Now you can yourself guess the reason why he mustn't do anything to over-exert his heart.
Might not the child be attacked in the same way if obliged to over-exert herself?
In his state of health, he's been fool enough to over-exert himself.
It is too far and Mrs. Case warns us not to over-exert, paddling.
You had better go with them, and see they do not over-exert themselves.