When someone overtrains, they train too much, usually in sports or exercise.
Overtraining can be bad for the body because it can make you tired or hurt.
Examples:
She overtrains for the race and now she is tired.
Overtraining can lead to injuries.
He overtrains every day and now he feels sick.
He overtrains so much that he falls asleep during the game.
She overtrains like a hundred hours a day!
Overtraining is like eating too much candy; it feels good at first, but then it makes you feel bad.