One of the machinist toys I built some years ago was a "finger treadle" Simple toy that has a place for a finger to press, connecting rod, and little 3" diameter flywheel.

I couldn't keep the rhythm to keep it spinning. My wife and kids didn't have any problem, but I would "miss a beat" on timing...

I can not post links at the moment, but google "Finger Treadle"

When I start wearing off my hands have a very difficult time typing, or controlling a mouse. When that happens I'll use microsoft voice recognition for email.