The studies add to earlier evidence that traditional bicycle saddles, the kind with a narrow rear and pointy nose, play a role in sexual impotence.
Some saddle designs are more damaging than others, scientists say. But even so-called ergonomic seats, to protect the sex organs, can be harmful, the research finds. The dozen or so studies, from peer-reviewed journals, are summarized in three articles in September’s Journal of Sexual Medicine.
In a bluntly worded editorial with the articles, Dr. Steven Schrader, a reproductive health expert who studies cycling at the National Institute for Occupational Safety and Health, said he believed that it was no longer a question of "whether or not bicycle riding on a saddle causes erectile dysfunction."
The studies, by researchers at Boston University and in Italy, found that the more a person rides, the greater the risk of impotence or loss of libido.
This does not mean that people should stop cycling, Dr. Schrader said. And those who ride bikes rarely or for short periods need not worry.
But riders who spend many hours on a bike each week should be concerned, he said. And he suggested that the bicycle industry design safer saddles and stop trivializing the risks of the existing seats.
"Most people are not riding long enough to damage themselves permanently," said the spokesman, Marc Sani, publisher of Bicycle Retailer and Industry News. "But a consumer’s first line of defense, for their enthusiasm as well as sexual prowess, is to go to a bicycle retailer and get fitted properly on the bike."
Researchers have estimated that five percent of men who ride bikes intensively have developed severe to moderate erectile dysfunction as a result.
But some experts believe that the numbers may be much higher because many men are too embarrassed to talk about it or fail to associate cycling with their problems in the bedroom.
The link between bicycle saddles and impotence first received public attention in 1997 when a Boston urologist, Dr. Irwin Goldstein, who had studied the problem, asserted that "there are only two kinds of male cyclists — those who are impotent and those who will be impotent."
The bicycle industry listened, said Joshua Cohen, a physical therapist in Chapel Hill, N.C., and the author of "Finding the Perfect Bicycle Seat."
Manufacturers designed dozens of new saddles with cut outs, splits in the back and thick gel padding to relieve pressure on tender body parts.
The area in question is the perineum, between the external genitals and the anus. "When you sit on a chair you never put weight on the perineum," Dr. Schrader said.
"But when you sit on a bike, you increase pressure on the perineum" seven-fold.
In men, a sheath in the perineum, called Alcock’s canal, contains an artery and a nerve that supply the penis with blood and sensation. The canal runs along the side of a bone, Dr. Goldstein said, and when a cyclist sits hard on a narrow saddle, the artery and the nerve are compressed. Over time, a reduction of blood flow can mean that there is not enough pressure to achieve full erection.
In women, Dr. Goldstein said, the same arteries and nerves engorge the clitoris during sexual intercourse.
