Meaning of the word "fit as a flea" in English

What does "fit as a flea" mean in English? Explore the meaning, pronunciation, and specific usage of this word with Lingoland.

fit as a flea

US /fɪt æz ə fliː/
UK /fɪt æz ə fliː/

Idiom

very healthy and strong

Example:
My grandmother, at 80, is still fit as a flea and goes for a walk every day.
After a month of intense training, he was feeling fit as a flea.