Recently I came across a good technical piano text by Wayne Hawkins of the jazz faculty at the University of Kansas, called "Piano Aerobics".
In his book, Wayne mentioned the following true story of his, I quote its entirety here:
"Back when I was still in my twenties, I had the good fortune to meet professional baseball pitcher Tom Seaver when I playing in a jazz club. I had an interest in pitching for baseball and he had an interest in jazz piano. I inquired about the technique in throwing a slider. He replied, "Well, show me how to play [the piano] like that and I'll show you." I responded, "Pretend you have a baseball in each hand. Turn your hands over and you will have good hand position [for playing the piano]....."
Wayne continued, "Here are some things to keep in mind regarding this technique:
- Turn both palms up.
- Put a baseball (or softball for larger hands) in each hand.
- Take care to not grip the baseball.
- Treat it more like an egg.
- Turn palms down and let baseballs drop.
- Place your hands over the piano keys."