As a mere mortal of speedrunning I've never touched on a game like NES Tetris and nor do I intend to 😂 But I've come to a point where to better a time in one of my runs to WR level I need to hypertap with my middle finger for short intense bursts, so the more windows of runs I can have per day the better my chances. I'm doing really good at it and eating more helps a bit (as in Xmas levels of sugary stuff, I'm being careful about that) but I am curious whether anyone much more used to constant hypertapping or mashing has any specific exercises they do to maintain or increase their finger stamina/power. At the moment I am not able to run as many times a day as I want to because I lose power.

Back when I was still trying to run Sword Master, my left thumb would start giving me major exhaustion pains halfway through just from the sheer amount of movement and diagonals I'd have to use. I'm not sure if it would increase stamina or power, but I used to slowly press each finger against one another with variable pressure (particularly the thumbs). After a few reps I'd slowly ball my hands into fists a few times with the thumbs alternately on the inside and the outside. I'm not sure if it actually helped, but the placebo effect might. To be fair, I couldn't run Sword Master more than once a day because my hands would be so exhausted.

As for hypertapping, I usually use my index finger and rapidly shake my whole arm while angling the controller away from me. I don't usually have to do any high-speed mashing in my runs, so my method might be slower. I may try it with the middle finger sometime to see if it works any better for me.

That's all I've got, though. I'm sure someone here has a secret method for improving mashing.

The trick is using both hands. Or at least multiple fingers, alternating. As someone who struggles with some minor hand pain daily even without speedrunning, save your hands, don't try to make single fingers faster - you'll just hurt yourself.

Exercise is unlikely to help with this much unless it's just stretching. Stretching is always good.