For a fitness story with legs -- and real public impact -- it's hard to top the one that ran in a 1997 issue of Bicycling magazine.

The article cited an unpublished study by nationally prominent urologist Irwin Goldstein suggesting that bike seats crush the main artery to the penis, causing permanent impotence.

Soon the story was picked up by "20/20" and an impotence warning was appearing in just about every article about biking and injury. Goldstein, whose comments in the initial article were somewhat guarded -- "I cannot say that sitting on a bicycle seat causes impotence," he told the magazine, and "I can't claim that long-term compression causes impotency, but I kind of think it does in a very small percentage of cases" -- was soon dispensing irresistible quotes, such as, "There are two kinds of cyclists: those who are impotent and those who will be." Even a single ride on the wrong seat can do major and permanent damage, he says, and the only safe way to cycle is on a recumbent bike.

Anxious to quell fears raised by these remarks, manufacturers rushed to produce anatomically contoured bike seats for both sexes. (Goldstein says women cyclists also face reproductive health concerns.) These presumably safer seats are now sold widely, but consumers still worry.

"[The issue] comes up every day," reports "Faruq" Robinson, a salesperson at City Bikes in Adams Morgan, who says bike shoppers regularly ask him if a cycle they are eyeing will cause numbness and harm their sexual ability.

He tells them the truth: He doesn't know. In fact, aside from the self-assured Goldstein, no one seems to know what to believe.

Four years after Goldstein's bombshell, many experts retain grave doubts about the evidence on which it rests. Goldstein's findings have never been reviewed and assessed by his peers, published in an academic journal or tested and replicated by other researchers.

And while other studies suggesting a link between cycling and genital numbness or impotence have been published in scholarly journals, experts say these reports are flawed. Biking on a narrow, rock-hard seat -- or any ill-fitting or uncomfortable saddle -- may numb your privates, but there's no clear proof that temporary discomfort or lack of feeling is linked to impotence.

Those at odds with Goldstein include four well-regarded urologists. Contacted for this article, each said that while it is possible for male cyclists to damage the sexual apparatus in an accident -- especially by smashing the crotch against the top tube, the horizontal bar between the seat and the handlebars -- the chances of doing lingering damage by just sitting tight and pedaling are very low.

"It's safe to bicycle," says William D. Steers, chairman of the urology department at the University of Virginia School of Medicine in Charlottesville. "That's an easy one. This whole [impotence-cycling] thing is really out of proportion. In China 90 percent of the male population cycles, and they don't seem to have a problem maintaining the population."

The cycling-impotence question, Steers says, has diverted attention from behavioral factors -- like smoking, overeating and inactivity -- that are far riskier to male reproductive health. "I find it disconcerting that attention to unhealthy behaviors hasn't been raised, when a healthful activity is getting this huge scrutiny."

Goldstein says he became convinced of cycling's ill effects after noticing in the mid-1980s that many of his male patients with complaints of sexual dysfunction were cyclists. He wondered if some of these problems stemmed from sitting on a narrow saddle for prolonged periods. His theory was that the saddle pushed into the perineum -- the soft tissue between the sit bones of the pelvis. Routed between those bones are the major blood vessels that feed the penis. Compressing soft tissue between a hard saddle and a hard bone, he suggested, was courting disaster.

After months of requests for copies of his initial study and a second one (also unpublished), Goldstein failed to provide much of that research for this article, saying the information was not readily available. But he agreed to describe his findings by phone.

According to the magazine article, Goldstein assembled a test group of 100 bike-riding men who had come to him for treatment of impotence. He measured blood flow to the penis while they lay flat on their backs and he applied pressure to the perineum with one of two cycling saddles or a chair. Goldstein says he found a 66 percent average reduction in blood flow from a narrow saddle, a 25 percent reduction from a wide saddle and no reduction from a chair. From this, he concluded that repeated compression of the penile artery would cause it to flatten or become blocked, which would eventually result in impotence.

Goldstein says he presented these findings at an American Urological Association conference. (He said he couldn't recall exactly when and where this meeting occurred, and the organization was unable to verify when Goldstein made this presentation.)

Goldstein says he followed his compression research with a second study, showing that cyclists had more than three times the impotence rate of runners, which he presented at another medical convention. Arthur Burnett, associate professor of urology at the Johns Hopkins Medical Institutions in Baltimore, calls this study, based on questionnaires to members of a running club and a cycling club, "terribly flawed."

"I think the premise was inflated; to presume that [cycling] is a major cause of erectile dysfunction in America is not correct," says Burnett. Goldstein's hypothesis, he says, "needs to be corroborated by other studies that show how real it is."

Goldstein says he's been too busy to submit his studies for publication in a peer-reviewed journal and that it's hard to find sponsors to pay for corroborating research. His critics, he says, "are welcome to their own opinion. I see patients with this problem all of the time."

Over the last two decades, more than a dozen studies examining the relationship between cycling and impotence have been published in medical journals. Steers says all of them have problems, such as an inadequate control population of non-cyclists of the same age and physical condition, and small sample size. "To power a study you need thousands of men," says Steers, while the largest of the published reports included only 160 men.

From where he sits -- with a professorship at the Boston University School of Medicine, honors from his professional colleagues and a practice where he treats as many as six patients a week for impotence that he believes is related to cycling -- Goldstein says he needs no further convincing. "If you sat in my chair, it would be clear. The impotent come in here, and I am the advocate for them."

While advocacy may not foster dispassionate research, it sells in the free market. Former emergency physician and inventor Roger Minkow used Goldstein's data to design a saddle with a channel cut to relieve pressure on the perineum. The Specialized Body Geometry saddle has sold 1.3 million units and sparked a design revolution. Minkow says his seat -- if it is properly fitted to the rider -- is as easy on the perineum as a chair. He also says he has research -- unpublished -- to back up this claim.

While the hazardous-saddle question remains unresolved, some riders clearly like having a choice of seat configurations. Says Robinson at City Bikes, "I had one of my customers kind of barge in on a crowded day and holler, 'Hey guys, my new saddle is great! My penis doesn't fall asleep anymore.' That's the level of enthusiasm." Split saddles, now a cycling industry staple, are designed for comfort -- and quelling fear.

Padded seats with channels, like the Tricot Split Rail, relieve pressure on the perineum.