Being “fit as a fiddle” means you’re in good health and in fine shape.
This expression dates from at least the 1600s. A fiddle that is fit is well-tuned and in good shape and can play terrific music, just like the human body. “Fiddle” was combined wth the word “fit” because we all love alliteration.
“Fit” didn’t originally mean healthy and energetic. When this phrase was coined, “fit” was used to mean suitable, seemly, correct, or proper, in the way we now might say, “fit for a purpose.” Thomas Dekker, in The batchelars banquet, 1603, said this: “Then comes downe mistresse Nurse as fine as a farthing fiddle, in her petticoate and kertle.”
Soon afterwards, in 1616, W. Haughton’s English-men for my Money includes: “This is excellent ynfayth [in faith], as fit as a fiddle.”
One theory suggests that: “As fit as a fiddle” used to be “as fit as a fiddler,” because a fiddler jumped and danced around so much while playing that he had to be in good shape.
However, it seems more likely to have arisen from the maintenance involved in keeping a musical instrument in good condition. Indeed, instruments like guitars, flutes, drums and others require a lot of care to keep them in good shape and functioning properly.
In order to keep a fiddle, or any stringed instrument, in a working state, its strings must be replaced if they break, tiny pegs need to be kept tightened, and it should be cleaned every now and then to prevent dust buildup.
Such maintenance keeps the violin healthy or “fit,” so to speak, just as going to the gym and working out keeps a human body in good shape.
Gym? What is this word “gym”? No, don’t tell me. It sounds like way too much work.