As you rise to the occasion, your penis contains spongy erectile tissue that fills with blood, thus determining the size of your erection. Unfortunately, the tissue isn’t easily changed, according to Walsh. "These fibrous cylinders are fixed to the pelvic bone, and by virtue of being fixed to the pelvic bone, they are not easily manipulated,” he says. “They are fixed in place, and for most men, the length of the penis that they achieve through puberty becomes their maximum length.”
Stretching with weights. Weights or stretching exercises won't bulk up your penis -- it's not a muscle. But hanging weights off your flaccid penis may stretch it a bit, O'Leary says. The catch is that it requires a freakish degree of dedication. "You might have to wear a weight strapped to your penis eight hours a day for six months," says O'Leary. At the end of it, you could be lucky enough to gain about half an inch. Risks include tearing of the tissue, burst blood vessels, and other problems.