I checked and found that the source the above ‘Phrase Finder’ response was the 15th edition of “Brewer’s Dictionary of Phrase and Fable.” After I looked at some other reliable sources, however, it was clear to me that the 15th edition of Brewer’s made the mistake of saying that the allusion IS, to street fiddlers, making it sound as if that were definitely known – it isn’t. The exact origin of the expression is unknown. But I do agree with the comment in #1962 that its staying power is probably due to its alliterative qualities. I was surprised to see that Brewer’s, a usually reliable source, would make such a mistake and then noticed that in the 16th edition they corrected their error (see below). The fact is, some think that the allusion is to the ‘fiddler’ and others think it is to the ‘fiddle’ and no one really knows for certain.
Brewer’s Dictionary of Phrase and Fable (16th edition)
AS FIT AS A FIDDLE: In a very healthy condition; in excellent physical form. The allusion is ‘probably’ to a street fiddler, who sways and swings about as he saws energetically with his bow. [[the ‘energetic’ did just fine in the 15th edition and the ‘sways and swings, saws, and bow,’ although colorful, add nothing new except extra words!]]
Facts on File Dictionary of Clichés
In excellent health, in good working order. The likening of human good health to a fiddle dates form1600 or earlier, but there is no completely convincing explanation of the analogy. It appeared in print in the early 17th century and was in John ray’s proverb collection of 1678. ‘Fit’ in those days meant ‘appropriate,’ as ‘fitting’ still does, but why a fiddle should be considered especially appropriate is unknown. It was only in the 19th century that the meaning of physical fitness was attached to the expression, where it remains today.
Facts on File Encyclopedia of Word and Phrase Origins
FIT AS A FIDDLE: Someone or something that is fit as a fiddle is, of course, in great shape. The common expression is about 400 years old, first recorded in 1616 in England, but that is all we know about its etymology. Perhaps a fiddle was considered fit because musicians always treated their instruments, the source of their livelihood, with tender, loving care [[how lame can you get!! How about the fiddle FIT in its case just perfectly!]]
Morris Dictionary of Word and Phrase Origins
FIT AS A FIDDLE means in tiptop condition. Its origin is obscure, but Charles Earl Funk [[of dictionary fame]], in his amusing ‘Heavens to Betsy,’ has the theory that two hundred years ago people thought of fiddles as instruments of great beauty—which, in the proper hands, they are. Anyhow, says Funk, ‘to have one’s face made of a fiddle’ was to be exceptionally good looking. To ‘play first fiddle’ was to occupy a leading position, and a man [[very un-PC]] was to occupy a leading position, and a man [[well at least he’s consistent]] ‘fit as a fiddle’ was beyond need of improvement in health.
Ken G – February 6, 2003