http://www.vice.com/read/yes-you-act...-your-dick-253
A group of Brazilian doctors recently published a paper in the academic journal Advances in Urology identifying "woman-on-top" (aka cowgirl) as the most dangerous sex position in terms of the sheer number of dicks broken mid-fuck. Analyzing data from three accident and emergency units in the Brazilian city of Campinas over the past 13 years for clear cases of penile fractures (in which the ligament in the penis either tears or overextends, often with a loud, painful crack), the doctors determined that half of all such fractures came when women rode men, with 29 percent resulting from over-vigorous doggy-style and 21 percent resulting from missionary sex.
Those who made it trough the wince-inducing study may have tried to take comfort in the fact that sex-related injuries are rare. As it turns out, that's not entirely true. Urologists at the University of Washington Medical School alone say they see at least one or two penile fractures a month. More generally, a British study found that up to five percent of the workforce takes time off for expressly sex-related injuries every year. And although there's a great deal of under-reporting, self-treating, or misreporting of sex-related injuries, most estimates say that up to one-third of adults will suffer some kind of injury during or directly from the dirty deed—often without realizing the pain they're in until the morning after, thanks to our lovely, sexed-up endorphins.
Many of these injuries could happen outside of carnal embrace: carpet burns, pulled muscles, sprains, and the like. But many more are fairly serious, associated with specific sexual scenarios, and utterly avoidable with the proper precautions.
To save ourselves some grievous harm at the most unfortunate of times, VICE dove into the literature on sex-related injuries and spoke with renowned sex therapist Dr. Kat van Kirk to create a list of the six most injurious heterosexual sexual positions and situations. (While there is overlap between heterosexual and homosexual sex injuries for both men and women, there are enough differences to merit their own future posts.)
Our rankings were based on the severity of injuries involved and the frequency with which practitioners encounter them. We also identified the safest heterosexual sexual position, and a few very simple tips to help you avoid serious harm in any position to make sure sex doesn't wreck your bits.
SIX OF THE MOST DANGEROUS HETEROSEXUAL SEX POSITIONS
WOMAN-ON-TOP / COWGIRL
The boys from Brazil were right about this one— it's fairly easy to hit things at the wrong angle and get a snap-crackle-pop when a woman puts her full body weight down on a penis.
"This issue is basically the woman's pubic bone," explains Dr. Van Kirk. "It's slightly differently positioned in each woman. At times there's not enough lubrication when the woman goes to sit on the penis if there's enough force or friction or the penis catches on the pubic bone, that's when that bend will occur in that ligament. That is more common than people think."
FYI: Apparently, the angle involved in reverse cowgirl is even more dangerous than cowgirl.