Many people who work with their hands find them sore and tired at some point. Book conservators are especially hard hit, since most of the time our hand skills involve depressing a small key a couple of millimeters while staring at a screen. Then we have to put in some long hours at the bench with a variety of knives, spokeshaves and other hand tools.
This exercise comes from Adrian Peter Schmidt’s 1901 Illustrated Hints for Health and Strength for Busy People. He self-published the book, and was the illustrator. Doing this exercise a couple of times a week has increased my finger, hand and forearm strength.

You simply take a sheet of newsprint, then proceed to crumple it up in your hand using only that hand. Then do the same to the other hand. Or do them both at the same time once you get the hang of it. Step two is to squeeze the crumpled ball a few times. That’s it.
He considers this deceptively simple exercise a warm up, to “stimulate energy in a mild way on mornings when you do not feel inclined to exert yourself.” I’m not sure how much energy it stimulates, but it certainly works the hands in what seems an even manor.
And I swear I’ve seen Schmidt walking around in Brooklyn.