Exercising too much, which can be bad for your body.
Overexercising can be seen as a negative thing because it can hurt your body.
Examples:
She is overexercising and not resting enough.
Overexercising can make you feel very tired.
He is overexercising every day and not taking a break.
I think I'm overexercising my brain with all this thinking!
She's overexercising so much, she's starting to feel sick.
I'm not overexercising, I'm just getting stronger!