Dr Jeroen Swart answers:
From the male perspective, making your wife pregnant requires you to have working sperm, and apparatus that works. The first is assessed clinically by measuring the number of sperm per unit of semen, and also the quality of those swimmers. Are they all the right size and shape, and do they swim with vigour?
A study conducted on cyclists’ semen has shown that cyclists produce the same volume, similar numbers of sperm and similarly-moving sperm (motility) as non-cyclists do. However, cyclists have a lower number of normally-shaped sperm (50% lower), and a higher rate of significantly abnormally-shaped sperm (500%) than their non-cycling brethren. This is most probably due to the tight-fitting shorts, and consequently the increased temperatures experienced around the scrotum during cycling. Those little guys need a cooler area to mature, which is why the scrotum allows the testicles to hang away from the body and run at a slightly lower temperature.
Which brings us to the second question: Whether cycling can cause your equipment to malfunction.
After a prolonged cycle race, between 4 and 25% of male participants experience penile numbness and
erectile dysfunction. The longer the race, the worse things get. These problems tend to resolve after a week or two, however.
In contrast, long-term studies indicate that cyclists have a similar incidence of erectile dysfunction to non-cyclists – or lower. This is probably due to the benefits of exercise on arterial health. But there are still a few factors that increase the likelihood of having ‘flat tyres’.
In both men and women, the skin and deeper tissues between the legs, and the external sexual organs, are supplied by the pudendal (deeper) and perineal (superficial) arteries and nerves. These all cross the perineum from back to front and can therefore become compressed anywhere along this course. Compression of either the nerves or arteries or parts of the sexual organs can cause pain, numbness and impotence.
The most common reason for this is excessive reach. To reach the handlebar, a rider extends the shoulders and flexes the upper and lower back. But if the reach is excessive, the extra distance can only be made up by forward rotation of the pelvis, or by moving the shoulder blades around the torso to lengthen the arms.
It is this excessive forward rotation that causes the front of the pelvic ring to be pushed into the front portion of the saddle, compressing the nerves and vessels. If you routinely ride with your elbows fully extended, then this may well pose a risk. Adjusting your stem, moving your saddle forward or switching to a smaller frame will probably resolve the problem.
An excessive saddle height causes rocking of the pelvis. This can cause repetitive trauma to the nerves and vessels as the saddle slides from side to side under the ischial tuberosities.
Saddle size and shape
The wings of the saddle are intended to support the sit bones. If the saddle width is insufficient then the ischial tuberosities slide over the edges of the saddle, and the pudendal and perineal nerves and vessels (which run just to the inside of the ischial tuberosities) are compressed between the saddle wings and the muscular floor of the pelvis. Your LBS should stock a pelvimeter to measure your pelvic width, and thus be able to recommend the correct saddle width.
Saddle width is the only saddle-related variable to be scientifically linked to erectile dysfunction. All other attributes – including those silly cut-outs – have no proven benefit whatsoever.
Dr Jeroen Swart is a sports physician and exercise physiologist at the Sports Science Institute of South Africa.