Many musicians complain of numbness and pain in the hand, forearm and arm. They can prevent repetitive strain injury, ease pain and tension by stretching regularly.
This finger exercise is one I learned at one of my early piano lessons, many moons ago. It's a hand exercise to strengthen those musical fingers, especially our very weak finger #4.
I detested it during those early piano practices, but I must say, my Finger #4's are better because of it. My students and I have dubbed it "Finger Push Ups":