Of course the 'fiddle' here is the colloquial name for violin. 'Fit' didn't originally mean healthy and energetic, in the sense it is often used nowadays to describe the inhabitants of gyms. When this phrase was coined 'fit' was used to mean 'suitable, seemly', in the way we now might say 'fit for purpose'.
Thomas Dekker, in The batchelars banquet, 1603 referred to 'as fine as a fiddle':
"Then comes downe mistresse Nurse as fine as a farthing fiddle, in her petticoate and kertle."
Not long afterwards, in 1616, there's W. Haughton's English-men for my Money, which includes:
"This is excellent ynfayth [in faith], as fit as a fiddle."
It means completely healthy, but it's not an idiom. When you see "AS ___ AS ___" you're dealing with A Simile.
As fit as a fiddle means to be in very good health.
As fit as a fiddle means to be in very good health.
As fit as a fiddle.
Fit as a Fiddle - in good health; in fine shapeorigin: This expression dates from at least the 1600s. A fiddle that is fit is well-tuned and in good shape and can play terrific What_is_the_origin_of_the_idiom_'fit_as_a_fiddle'. So , it was combined wth the word 'fit' to become an alliteration.
to be healthy
It means to come in behind someone else, as if they were the first fiddle in the orchestra and you were the second one. The second fiddle in an orchestra supports the first one and plays harmony for them - someone who is playing second fiddle supports the other person and backs them up.
As fit as a fiddle means to be in very good health.
As fit as a fiddle means to be in very good health.
As fit as a fiddle
As fit as a fiddle.
I feel fit as a fiddle today.
Fit as a Fiddle was created on 1997-03-11.
Fit as a Fiddle - And Ready for Love - was created in 1932.
Fit as a Fiddle - in good health; in fine shapeorigin: This expression dates from at least the 1600s. A fiddle that is fit is well-tuned and in good shape and can play terrific What_is_the_origin_of_the_idiom_'fit_as_a_fiddle'. So , it was combined wth the word 'fit' to become an alliteration.
to be healthy
You are fit and healthy!
fiddle
It was about as fit as one!