Quartz has a piece with tips on handwriting, where exercising your hand and lower arm is mentioned:
Typing doesn’t build the hand and finger strength necessary to hand-write for long periods, Blain points out. Squeezing a stress ball can help with that. So can stretching out your writing hand to avoid arm injuries. An 80,000 word hand-writing binge last November landed Blain at a physical therapist for an elbow injury, because she hadn’t stretched out her arms or taken enough breaks.
Useful advice if you’ve a mind to write a longer piece, a book perhaps, by hand.