Does working out in a gym affect piano playing ?
Does it makes your fingers hard ?
Physical fitness is crucial for a good solo piano performance, naturally. From my own experience, piano playing is exercise enough for the fingers and lower arms, but the rest of the body should be exercised separately, especially when studying pieces that demand lots of physical energy, such as Beethoven piano sonatas.
About the fingers .. Once, when preparing for a solo piano recital, I tried strenghtening just my fingers by using those whattayoucall'em... hard rubber rings you squeeze to increase hand strength? .. but I found my fingers were becoming more "clumsy" and the playing precision was becoming worse, so I quickly dropped that exercise.
(EDIT): I didn't go to the gym when practicing, I just used old-fashioned exercises like running and push-ups so I cannot comment on the direct relationship between using exercise machines and piano playing..
I think the most important thing to never overlook is stretching properly and "everytime" you workout regardless of wieghts, running or whatever.
I personally recommend more demanding stretching like yoga or similar. Not only does it make you very limbre/relaxed(muscles), it is a workout as well in addition to wieghts. Streching also lengthens the muscles. Ever see those guys who bulk up but tend to just show BULK and start looking a bit clumsy in movement? They do not stretch. The muscles/tendons start tightening up into "balls". So stretching(properly) imho is probably the most important thing to do, well there is diet as well lol
I personally prefer the yoga stuff(learned most on the internet) as it has many benifits on its own. You can stay limbre/relaxed, helps to keep focus, increases circulation, ect ect ect. It also as I have noticed tends to keep the bulky/clumsy look at bay and creates a more "lean muscle mass" look.
I'm a Masters Swimmer. Swimming definitely builds hand strength, but with the hand open. It's not a gripping or closed fist exercise, nor is it a "power" exercise, so it's probably more compatible with piano and string playing.
That said, there is no doubt that the hands (and most everything else) are fatigued after a few thousand meters. Don't schedule your piano lessons or a recital right after swim practice!
Another thing to consider is the difference between a regular athlete and somebody who has just decided to get into shape. When you start a new workout, you're using untuned muscles. Progress is slow and you ache for the first weeks. I think you have to reach an equilibrium before judging how an exercise will affect piano playing. Some years ago I went waterskiing for the first time. That night I couldn't play a simple bar chord. The problem wasn't waterskiing. The problem was that I spent the day using muscles that didn't hardly exist!
Exercising your hands causes a continuos ringing of concert A in your ears. As symptoms progress you'll begin having late night visions of pre - 20th century composers who compell you to write 3 chord orchestral riffs, while the percussion section gets extended solos....