This may be old news, since the WSJ piece on yo-yos ran in July, but check out this angiogram of yo-yo pro Dave Schulte’s hand, in particular the lack of circulation in his index finger due to crushed veins:

So I had a look around to see what kind of yo-yoing could wreak such havoc. Looking into competition, my head was turned by two divisions; 4A, where the yo-yo isn’t actually attached to the string (!) and 5A, where you don’t loop the yo-yo around your finger, as it instead has a counterweight on the other end. YouTube has HD video of the 2008 Asia Pacific 4A champion and the 5A champion.
(via tmn)
