Cyclists beware! Pressure from seats can do lasting damage

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Riding bicycles is undoubtedly good for us: great for fitness, cardiovascular health, and burning off those delicious high-energy foods when we over-indulge. But a range of insidious chronic ailments can affect cyclists who spend extended periods on their bikes.

Research published recently in the Journal of Sexual Medicine suggests that regular cycling can potentially affect the sexual health of women. While not a new idea, the latest work finds that what matters most is the configuration of the bicycle and its consequences for riding position.

Reports dating back many years indicate that excessive cycling may lead to infertility in males. This is probably due to impaired thermoregulation of the testes, which must be kept cooler than internal body temperature to maximise healthy sperm production. But another family of genital complaints has a different cause. Most common is genital numbness, or loss of feeling, potentially leading to erectile dysfunction.

To understand how these conditions arise from cycling, let’s look more closely at the anatomy of the pelvis and genitalia, together with the nerves and blood vessels supplying the area.

Under pressure

Biomechanically, the pelvis is a series of boney arches connecting between the lower vertebral column and the legs which can absorb very large loading forces. When we sit upright, with our legs flexed forwards at the hips (as when sitting at a desk, for example), our weight is supported by an expanded part of the pelvis deep in each buttock (the “ischial tuberosities”).

Our external genitalia (male or female) sit below the front arch of the pelvis (the “pubis”) and are mostly out of the way in a normal sitting position.

A microscopic image of the clitoris of a female guinea-pig. All the fine red structures are the ends of sensory nerves, which connect up to the pudendal nerve. Modified from Vilimas et al (2011) in the Journal of Sexual Medicine.

A microscopic image of the clitoris of a female guinea-pig. All the fine red structures are the ends of sensory nerves, which connect up to the pudendal nerve. Modified from Vilimas et al (2011) in the Journal of Sexual Medicine.

But things change if we assume the extreme forward-leaning position that cyclists employ to reduce wind resistance. The weight of the body onto the bicycle saddle is still taken mostly by the ischial tuberosities, but the hips are flexed and the pelvis is now tilted forward. This orientation can create undue pressure between the genital region and the bicycle saddle.

Excessive pressure on the genitalia can cause local inflammation and swelling. A less obvious problem, however, is pressure on the nerves and blood vessels that supply the genitalia.

The external genital tract has a rich blood supply necessary for erection and glandular secretions during sexual activity. Changes in blood flow are regulated by a complex system of nerves that mostly operate without our conscious control.

Losing your nerve

Another set of highly sensitive nerves respond to mechanical stimulation of the genital tract. The endings of all these nerves communicate with the spinal cord via a major neural pathway, the “pudendal nerve.” The trouble for cyclists is that this nerve, and its associated blood vessels, pass very close to the pubic region of the pelvis on their way to the genitalia.

When in their characteristic streamlined, forward-leaning position, cyclists can put excessive pressure on the pudendal nerve, as the front of the saddle pushes up against the pubis. Nerves don’t cope well with constant physical pressure. At first, the pressure produces abnormal firing patterns, which are interpreted by our brains as the feeling of “pins and needles”. This strange feeling should be read as a warning sign: your nerves are potentially in trouble!

The forward-leaning position of cyclists creates undue pressure between the genital region and the bicycle saddle. Melvin Schlubman

The forward-leaning position of cyclists creates undue pressure between the genital region and the bicycle saddle. Melvin Schlubman

If pressure on the nerve is not released, the nerve fibres may no longer transmit their messages. Should the damaged nerves be sensors, we experience numbness in the area they usually monitor; should they regulate blood flow, functions dependent on blood flow, such as erection, will fail.

The situation is compounded if the blood vessels themselves are also compressed. Maintained blockage of blood flow to any part of the body will lead to oxygen deprivation and potentially death of the tissue.

Not the end

So what can cyclists do about this? Options include changing saddle design to reduce pubic pressure, and making sure you rise up off you saddle when going over rougher terrain. And the research in the Journal of Sexual Medicine finds that simply raising the handlebars a little compared with the height of the saddle, thereby slightly reducing the pressure on the pudendal nerve, can significantly reduce genital numbing in female cyclists. Although they didn’t examine longer-term effects, the implication is that this will reduce the risk of impaired genital function.

As valuable as these new observations are, it is important not to devalue the nett health benefits of cycling for most people. Nevertheless, perhaps we should heed the advice of the Irish novelist, Flann O’Brien (Brian O’Nolan) in The Third Policeman and his theory of “atomics”, later upgraded to the theory of “mollycules” in The Dalkey Archive: “The gross and net result of [excessive cycling] is that people who spend most of their natural lives riding iron cycles over the rocky roadsteads of this parish get their personalities mixed up with the personalities of their bicycle as a result of interchanging of the atoms (mollycules) of each of them and you would be surprised at the number of people in these parts who are half people and half bicycles.”

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