the bullshit stoners and anti cannabis people come up with... ill never understand. smoking cannabis will not make your muscles weaker or make it harder for you to get stronger. anything you put in your lungs that isnt supposed to be there is more than likely not going to be good for you. i will say that if youre hitting the bong multiple times a day it's going to affect your lung capacity. do some breathing excersises and some cardiovascular work outs to counter act it.