And some bicycle saddle designs are more damaging than others, scientists say. But even so-called ergonomic seats, designed to protect the sex organs, can be harmful, the online edition of The New York Times reported.
According to research studies published in The Journal of Sexual Medicine, when riders sit on a classic saddle with a teardrop shape and a long nose, a quarter of their body weight rests on the nose, putting pressure on the perineum or lower pelvic region.
The amount of oxygen reaching the penis typically falls 70 percent to 80 percent in three minutes. "A guy can sit on a saddle and have his penis oxygen levels drop 100 percent but he doesn't know it," Joshua Cohen, a physical therapist, said. "After half an hour he goes numb." "Numbness is your body telling you something is wrong," said Irwin Goldstein, a Boston urologist.
Today's ergonomic saddles have splits in the back or holes in the centre to relieve pressure on the perineum. But this may make matters worse: the ergonomic saddles have smaller surface areas, so the rider's weight presses harder on less saddle, Steven Schrader, a reproductive health expert, said.
The arteries in the perineum can come under more pressure when they come into contact with the edges of the saddle. Thick gels on saddles can also increase pressure to the perineum because the material can migrate and form clumps in all the wrong places, the study said. Just as many smokers do not get lung cancer, many cyclists will never develop impotence from bicycle seats, the scientists said.
What makes one person more vulnerable than another is not known. Body weight seems to matter - heavier riders exert more pressure on saddles. Variations in anatomy may also make a difference.
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, 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."
Manufacturers designed dozens of new saddles with cut outs, splits in the back and thick gel padding to relieve pressure on tender body parts.
This does not mean that people should stop cycling, 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