my sons age is 12and 1/2 for his skating purpose can he do gym to develop his thigh muscle,by lying on a machine and pushes the weight by his leg,around60 kgs,what r the side effects by doing this he does not lift it on his shoulders ,iheard some telling for boys gymming s not good and in future their sperms nos will reduce. is that true or not Doctor can u suggest me ,he started a month back.whether to continue it or not. thankyou Dr