Hi, thanks for writing to HCM.
There is absolutely no relationship or correlation with masturbation
and weakness in the bones and joints. Its more a psychological issue -The more you think of it, the more weakness you feel.
I suggest you to concentrate more on you academic career, have a healthy life style, take a balanced diet rich in fruits and vegetables along with calcium supplements
Develop a positive attitude and go ahead.
Hope this information is helpful. Good day