I have trained about 8 to 10 and work with 6 different players currently,, a couple have had these issues and was worked out once the grip was fix and the arm strengthened to deal with the new muscle memory that was built.
Also I have had to deal with more injuries due to the nature of sports I have experienced with over the years , you tend to learn a few thing over the years with experience.
Fair enough. But most would still not recommend poly at high tension and stiff frames for young kids.
"More Sureshs, less Maxima for a better TT." - Power Player