I am just gonna post my personal experience here. I had been doing cardistry for almost 2 years now and in the past 6 months, after learning bullet and kryptonite and etc, I started feeling a kind of numbness and tingling in my left hand's fingers. After doing some research and consulting a neurologist, I found out that I have CTS(Carpal Tunnel Syndrome). If you dont know what it is, it's basically a problem in which the carpal tunnel in your hand becomes smaller and starts putting pressure on your median nerve which is what we use to move our thumb, index and middle finger. It is caused by excessive repettetive wrist work. (Which I do a lot while practicing cardistry). It is fairly dangerous since after a while, your hands could be paralysed from wrist down completely. I dont say this will happen to everybody but it might, so be careful how much you are using your hands.
P.S. Shin lim has the same problem, which is why he doesnt play the piano anymore.
P.S. Shin lim has the same problem, which is why he doesnt play the piano anymore.