Sir I m a sports person. Somtime I mastabate. Some of my friend says mastabation makes people thin and weak? Is it true? Please tell me

Possibly. Sperm production has been shown to be physically tolling on the body and it might even be one of the many reasons women have longer lifespans than men. However if you masterbate on occasion, hydrate regularly and sleep well you should be fine. Most sports related weakness is due to dehydration.