It's been one of the more enduring concerns for men who have taken up cycling in the past couple of decades.
Yes, riding a bike is a great way to get fit and stay healthy. But can sitting on a bike saddle for extended periods be a cause of erectile dysfunction and urinary problems?
In the past 20 years, a number of studies of cyclists have issued warnings about the possible effects of pressure on the perineum – the area between the legs that holds vessels that transport blood and urine.
But research published this month in the US Journal of Urology has drawn an interesting comparison between different sports.
The multinational study (which included Australia) compared three groups of male athletes – 2774 cyclists, 539 swimmers and 789 runners – who were surveyed using Facebook ads and outreach to sporting clubs for athletes.
Participants completed a range of questionnaires focusing on sexual health and prostate symptoms, and answered questions about urinary tract infections, urethral strictures and genital numbness.
"This is the largest comparative study to date, exploring the associations of cycling, bike and road characteristics with sexual and urinary function using validated questionnaires," said lead investigator Dr Benjamin Breyer, of the University of California in San Francisco, in a press release.
Cyclists were also asked a range of questions including about their choice of bike, saddle, saddle angle and whether they wore padded shorts. They were also divided into a high intensity group (men riding for more than two years who rode at least three times a week with a daily average of more than 40km) and a low intensity group.
So what were the study's conclusions?
"In general, when compared to swimmers and runners, cyclists' sexual and urinary health was comparable, although some cyclists were more prone to urethral strictures," the study found.
High-intensity cyclists also recorded slightly better erectile function scores than low-intensity cyclists.
"The difference wasn't huge at all," Breyer said by email. "I think a possible theory is that high-intensity cyclists have a bike that is professionally fit (important to limiting perineal trauma), they are in better shape and more careful to avoid trauma."
While he believed the benefits of cycling far outweigh any risk, "I would avoid numbness wherever possible," Breyer said. "Getting a bike that is fit to your body is critical to protecting yourself."
Professor Eric Chung, Head of the Andrology Group for the Urological Society of Australia and NZ, agrees that strategies to prevent excessive pressure are important.
"If someone cycles a long period of time whereby they are constantly having pressure round the perineal area, and depending upon the type of bicycle they use – especially the seat design – that can put more pin-point pressure onto some nerve and vascular bundles and that can increase the risk of health problems."
Staying fit and healthy is important and cycling was an exercise he would definitely recommend, "but if people start complaining of any adverse symptoms they need to seek appropriate advice," Chung said.
Of course, many sports cyclists find a comfortable fit through advice and careful choices when purchasing their bike and saddle, and by trial and error (and personal research) when adjusting their set-up.
Key contact point
But there are those who turn to a bike fitter for assistance, especially if they are struggling to find a comfortable position on their bikes.
"Saddle comfort is something a lot of people battle with," says Andrew Steel of Body Care Solutions in Melbourne. "It's a key contact point for riding the bike.
"I had a customer who had been riding for three or four years who just thought numbness in that area was normal … he thought everyone had it," Steel said. "And it wasn't until I asked him that specific question about saddle comfort, that he mentioned he always found it hard to urinate after getting off the bike."
Neill Stanbury, of Neill's Bike Fit in Melbourne, says that many riders of both genders suffer in silence with bike discomfort "or they curtail their distance – they say, 'oh, if I ride more than 50km I get a lot of pain, so I just ride 40ks. They simply think 'I'm middle-aged, I'm on a road bike, things are bound to hurt', and so they'll put up with knee pain, saddle pain, whatever."
While saddle choice can make a lot of difference to a rider in discomfort, Stanbury says the first approach is to "fix the position", making sure that saddle and handlebar height, cleat position and all other aspects of the bike's geometry are suited to the rider. "Once the position is fine and there's still a problem, then we'll try changing saddles," he says.
Eliot Denver of Body Mechanic in Sydney agrees that a correct position is the first step, but says that improved saddle design – especially saddles with a "cut-out" section in the middle – has helped to increase comfort for some riders.
"If anyone has any discomfort in the perineal area – both males and females – we'd recommend a saddle with a cut-out, which essentially takes the pressure off that area," says Denver.
More streamlined riding positions – either when the rider is holding the "drops" (the lowest parts of racing handlebars) or using elbow supports on a time-trial bike – are when saddles with cut-outs are especially helpful, Denver says.
"Obviously, a female pelvis is broader than a male's. So if I'm looking at someone sitting on a saddle, be they male or female, you need to get good pressure on the two bones in your bum called the ischial tuberosities – they need a saddle that's an appropriate width.
"It's about getting the right shape and the support where you need it and relief where you don't need pressure."
Studies into the effects of cycling are ongoing, with Breyer's team now "looking more closely at those who reported numbness to see if this is a predictor for future problems".
Meanwhile, one finding of the study was that increased standing on the pedals while cycling was associated with lower odds of numbness. It's a good reason to keep attacking those hills.
Fairfax journalist Michael O'Reilly has written the On Your Bike blog since 2011.