I use 'fit as a fiddle' for a general statement of health, and 'fighting fit' if I have something to do that needs energy or effort to achieve (and I use it as a statement of physical or mental readiness for battle!). I guess you could say that if I'm fighting fit - I'm ready for battle!

Hi Anoush, I honestly never heard of “fit as a fiddle”, but my initial thought is this refers to someone who has great cardiovascular endurance and, because of this, great energy. Now, “fighting fit” is a little different. This would be a person who has great cardiovascular endurance AND muscle strength. “Fighting fit” doesn’t mean they are trained to combat. It basically means that they can defend themselves if they ever need to, because they are so fit and strong. I hope this helps 🌈 Nicky

Hi Anoush, Fit as a fiddle is probably used more for someone who is naturally fit while fighting fit is used for someone who tries and exercises to stay in shape. You don't hear these idioms too often, rather we'll probably say he or she is very fit.

I would never say either. ‘Fit as a fiddle’ sounds old-fashioned. ‘Fighting fit’ isn’t common enough to be idiomatic but implies that the fitness is for a purpose.

These are not used very often. 'Fighting fit' could be how you refer to someone after they have been unwell but is now better or ready to resume their previous level of activity.' Fit as a fiddle' is an old saying but basically means very well.