You need to be examined thoroughly. Shrinking and trembling can be due to many cause from some functional or mental to neural or muscular diseases. doing hand practice is common and if it is in controlled frequency then not harmful at all. So if your limbs are shrinking then there can be some other reasons too.
Next Steps
So don't be shy and consult Homeopathic consultant who will diagnose your problem and cure it. And also will help you controlling your hand practice if needed.
Health Tips
Don't be judgemental and don't be shy. Visit Doctor and get yourself thoroughly examined.