Oh no, I didn't say that the penis was a muscle. In fact, I did some research on qfac.com, a site for exersizes/muscles and that sort of thing.
Originally Posted by http://www.qfac.com/articles/love_muscle.html
By now with the Viagra kick flying in high gear, most guys know about the blood holding spongy tissue of the penis and why it's so important to erections. Some guys even know about a particular muscle called the Pubo Coccygeal (PC), that helps maintain your erection and can control premature ejaculation.
But the PC is not the do all-end all of penis muscles! In fact aside from maintaining your erection, the PC does little to contribute to the overall size and thickness of the penis. What most folks don't know is that besides the spongy tunnel that holds blood, the thickness of the penis is determined by two muscles; the Ischio Cavernous (IC) and Bulbo Cavernous (BC). These two sheets of voluntary (striated) muscle wrap around the shaft of the penis like the belts on a radial tire. When pumped and contracted they give added rigidity and thickness to the shaft. As with any of the voluntary muscles, these can be exercised and both their strength and size improved.
I don't belive they mean masurbation increaces size, as said on Jackinworld.
In conclusion, the penis might get somewhat bigger through sertain exersizes. I wouldn't take the time to do it, unless I was an adult and my penis was under 5.2 inches or so.