There are products out there like finger weights, grip strengtheners or weights that supposedly make your fingers longer. I won't link to any of those pages from here, because I don't want to give them any more traffic. These devices were very popular in the late eighteenth and early nineteenth century; Clementi made a big part of his fortune by actually inventing one. There's a reason why people stopped using them. They don't work. Not only do they not work, you can injure yourself to the point where you will never play again, which is what happened to Schumann.
We use very small muscles to play the piano, and we don't need a lot of strength to play. Using these devices to get better at the piano is like hanging weights from your ears in the hopes that it will give you perfect pitch.
DON'T USE THEM.