Flann O'Brien famously advanced the "Mollycule Theory" in The Third Policeman, according to which "people who spend most of their natural lives riding iron bicycles over the rocky roadsteads of the parish get their personalities mixed up with the personalities of their bicycles as a result of the interchanging of mollycules of each of them". Unfortunately, the truth of the relationship can be a little less romantic.
Down there. It's not the most transcendent of themes, but sooner or later, every cyclist has to deal with it. Not surprisingly, it is a sensitive and touchy subject.
Bum just about covers it, but the vernacular simplifies quite a complex junction. When you sit on a bike saddle, your weight is borne at three pressure points: two are bony - your ischial tuberosities, or "sit bones"; one is soft tissue - the perineum. The difficulty with the latter is that this strip of flesh carries arteries, vessels and nerves that supply the genital area - and which get squeezed when you ride a bike. It is this fact that led a urologist named Dr Irwin Goldstein to make his notorious 1997 claim: "There are only two kinds of male cyclists - those who are impotent and those who will be impotent."
Apart from the fact that even professional cyclists seem able to procreate, one's own anecdotal experience would, it is hoped, suggest that Goldstein was overstating his case. Still, the idea of a link between cycling and erectile dysfunction took root, so to speak, even though the evidence is at best contradictory. Two Boston-based studies, for instance, found slightly higher rates of ED among cyclists (4%) than among runners (1%) or swimmers (2%). But we would need to know the age of the cyclists concerned, since the rate of impotence in the general population is thought to be about 2% for 40-year-old men and 25% for 65-year-olds - averaging out at perhaps 10% for men of all ages.
Impotence, anyway, is not the whole story; or even part of it, for female cyclists. Such studies as there are suggest that women experience many of the same issues as men: soreness and chafing, "saddle sores" (cysts), and nerve damage and numbness (the "numb nuts" phenomenon, as it is known, among male cyclists). When I interviewed the great Irish cyclist, Sean Kelly, recently, he told me that he had pain peeing for three days after the Paris-Roubaix race. But that's what you get for riding more than 250km in a day, large chunks of it over murderous cobbles.
Yet it's not all grim down south. These problems are manageable: a bike that fits well, wearing padded shorts and shifting position frequently all help. As does pedalling harder - it means more of your weight is carried by your legs - and avoiding cobbles.
But the real clincher is the mound of medical evidence about the cardiovascular benefits of exercise. One doctor researching exercise and sexual function among men with heart problems compared the effect of cycling with that of Viagra. In general, anyone who exercises is likely to enjoy a better sex life, while obesity, diabetes and heart disease all correlate with ED. Aerobic exercise also helps beat depression, commonly associated with loss of libido.
So, it isn't so bad to be one of those people O'Brien's police sergeant spoke of "who are nearly half people and half bicycles". Perhaps his real point was that cycling, like sex, is as much in the head.
Bike doc
Dear Matt
My left leg bends only 90 degrees following a motorbike accident. But my young daughter would love me to go cycling with her. Is there any form of cycle I could use? Dorothy Byrne
If the saddle is at a correct height (your leg should be nearly straight when your foot is at the furthest extent of the pedal stroke), you would barely bend the leg past 90° anyway. Have you tried cycling on a conventional bike with the saddle as high as it will comfortably go? You may have to ride higher than the ideal, but at least you could ride.
Assuming you have tried this and it doesn't serve, then options are, I'm afraid, rather limited. There are hand-cycles for more severely disabled people, but that seems too extreme a solution for your needs.
I have seen people cycle very effectively one-legged. It may work best if you use a fixed-wheel bike, and that would take some practice. But if this were to be the best solution, then you would want a bike adapted with a footrest for your left leg, which would need some consultation with a specialist frame-builder.
· Please send your cycling queries to bike.doctor@theguardian.com