Well after 6 pages that I quickly skimmed, I saw lots of discussion about arm muscles. It's the fingers that do the work. Well I guess the muscles that control the fingers are in the forearm..
My playing table tennis proofed that the fingers deliver the power. Playing baseball I learned that the fastball and change up and curve or slider All had the same body and arm movements. The fingers could change the pitch. A pitcher had to be able to disguise the pitch. With the same visible delivery, the subtle input of the fingers was much harder for a hitter to detect.
Piano players tickle the ivory. The subtle input from wrist and fingers deserves attention.
Most shots get a gentle caressing the break shot gets a bitch slap.

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