I have heard from a (usually very knowledgeable) friend before, that a human can only tap his fingers 7 times per second.
I generalized this to "our muscles are limited to 7 hertz"
When my wife heard this she was like "no way, I'm faster" and we recorded a video of her blinking as fast as she could (her eyes hurt afterwards) and over 5 seconds she averaged exactly 7 blinks per second.
I can't find any articles on the subject, but I did find this video of a drummer doing 1208 beats in 60 sec, setting him up at 20.13hz, meaning 10hz each hand. However if you look at his hand, his muscles are not even really tapping, they are just in a vibration (like a spasm), while holding the drumsticks, which than do all the tapping...
Ussain Bolt sprinted 100m in 9.6 seconds, with 41 steps, that's a little over 4 steps per second.
Both these are very impressive. The drummer sticks out for coordinating his 10 taps per second on each hand, alternating with the other hand, while the motion is certainly faster then our eyes can see.
So what's up with the 7 Hz speed limit? Is it a thing, or did the drummer disprove it? Could the 100m world record be beaten by another 25% when we can find a tall guy capable of doing 7 or even 10 steps per second?