Perineal injury: release the pressure

Andrew Hamilton investigates the causes of saddle-induced injury in cyclists and what the science says about reducing injury risk

Compared to many sports, cycling carries a relatively low risk of injury, thanks largely to the smooth, impact-free and supported nature of the pedaling action. However, the interface between the cyclist and the bike (at the handlebars, the pedals and the saddle) has the potential to produce injuries, with the greatest sustained forces being experienced in the saddle region, between the surface of the saddle and the groin.

Pain in the perineum

Although cyclists tend to talk of a ‘sore bum’ after hours in the saddle, it’s the perineum (the narrow area running forwards from the anus to the scrotum – see figure 1) that usually falls victim to pressure-induce trauma. The perineum lies just below a sheet of muscles called the pelvic floor muscles, which support the bladder and bowel. The perineum region is sensitive and vulnerable to injury because it contains blood vessels and nerves, which supply the urinary tract and genitals with blood and nerve signals.

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Figure 1: Anatomy of the perineum

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Compared to sitting in an ordinary seat, bicycle saddles are much narrower and smaller – an inevitable consequence of the need to allow an efficient pedaling action – ie with the feet aligned roughly under the hips. The smaller area means cyclists will experience more force per unit area (pressure), while the narrow design tends to transfer that pressure to the perineum area. To make matters worse, saddles are relatively bereft of cushioning, which means that jolts, impacts and general ‘road buzz’ are easily transferred from the road, through the bike to the rider, increasing the degree of trauma experienced.

All of these factors can result in cumulative injury to the blood vessels, nerves, and muscles in the perineum, leading to various urogenital complications such as bladder control and sexual problems and erectile dysfunction (see box 1). The evidence suggests that this problem is widespread, and studies indicate that up to 91% of cyclists have experienced nerve entrapment syndromes at some point, resulting in symptoms of genitalia numbness⁽¹⁾. In around 20% of cyclists, this was also followed by erectile dysfunction. Although these symptoms tend to be temporary and reversible in the early stages, they can become chronic, and lead to more serious conditions such as infertility and prostatitis (inflammation of the prostate gland).

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Box 1: Sexual health problems caused by perineal trauma

The perineal nerves carry signals between the genitals and the brain. Injury to those nerves can interfere with the sensations of sexual contact. Signals from the brain direct the smooth muscles in the genitals to relax, causing greater blood flow into the penis. In men, damaged blood vessels can cause erectile dysfunction (ED), the inability to achieve or maintain an erection firm enough for sexual intercourse. An internal portion of the penis runs through the perineum and contains a section of the urethra. As a result, damage to the perineum may also injure the penis and urethra.

Male cyclists who ride for several hours a week are particularly vulnerable to perineal damage. In addition to the reduction of genital sensation, the repetitive pressure on the blood vessels can result in constriction, leading to the build of plaque. This in turn reduces blood flow, which can lead to erectile dysfunction.

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Saddle design

Padding and width - The anatomy of the groin can’t be altered but the way it interfaces with the bike can - by choosing an appropriate saddle design. However, the research is far from clear cut as to what design works best – not least because of the large inter-individual variations in anatomy. In one study, researchers investigated the amount of perineal pressure generated in men who cycled while using four different bike saddle designs⁽²⁾:

1. A narrow heavily padded seat.
2. A narrow seat with medium padding and a V-shaped groove in the saddle nose (figure 2).
3. A wider unpadded leather seat.
4. A women's special wide seat with medium padding and no saddle nose.

Despite having more padding, saddle #1 produced greater perineal pressure than saddle #2. And although it was unpadded, saddle #3 produced less perineal pressure than #1 or #2. However, it was saddle #4 (the wide design) that produced the lowest perineal pressure, indicating that adding padding is less effective at reducing perineal pressure than increasing saddle width.

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Figure 2: Saddle with V-groove

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Nose length - Saddle nose length also seems to be a factor. In a 2014 study, researchers found that longer saddle nose lengths produced greater subjective feelings of perineal discomfort, and that lengths of 0-3cms were the most comfortable⁽³⁾. Unfortunately, these very short nose lengths had the downside of reducing the riders’ stability, especially when riding on the drops. With a nose length of 6cms however, this instability was eliminated yet the riders still reported high levels of comfort.



Cut-out design - A wide saddle and short nose reduces perineal pressure, but for serious cyclists, these designs are less appropriate, being both less aero and less stable when riding in a low position. In recent years, an extension of the V-grooved design has become popular – the cut-out design (figure 3) – where the center section of the saddle under the perineum) is abolished completely. With no direct pressure on the perineum, this design should (in theory) be effective.

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Figure 3: Cut-out saddle

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A study on female cyclists compared seat pressures and genital nerve function in 48 women cyclists who normally rode either using traditional (non cut-out) saddles or cut-out saddles⁽⁴⁾. However, contrary to expectation, the results showed that the cut-out design did NOT reduce saddle pressures over a traditional design. In fact it slightly increased them, although there were no differences in nerve sensation.

These results are similar to an earlier study, which found that cut-out saddles increased seat pressures compared to a traditional gel-cushioned saddle⁽⁵⁾. Why is it that the cut-out saddles seemed to confer no benefits? One explanation is that although there’s no force applied to the area directly under the perineum, the cut-out design results in increased forces along the edge of the cut out, which are then transferred to the perineal area. Also, with less surface area than an equivalent-width non-cut out saddle, the actual seat pressures are higher overall.

Saddle positioning

Regardless of design, correct saddle positioning is vital. In particular, if the saddle height is too great, perineal pressure will be increased, particularly at the bottom of the pedal stroke when the foot is near the six o’clock position. The saddle angle in relation to the ground is also important. The usual recommendation is that the saddle should be horizontal and the nose of the saddle should never be higher than the seat. However, there’s evidence to suggest that a very slight downward tilt (so the nose is slightly lower than the seat) can help to reduce perineal pressure⁽⁶⁾.

Seat of the pants

Cycling short inserts claiming to reduce pressure and increase comfort have become commonplace in modern cycling clothing. Many of these products are undoubtedly comfortable, but some research suggests that perceived comfort is not always a good guide to the perineal protection offered. In one study, club cyclists rode for 20 minutes while wearing cycling shorts fitted with three cycling short inserts, each of different design and thickness⁽⁷⁾. Surprisingly, the cyclists’ ratings of comfort didn’t tally with the actual perineal pressure readings – ie the most comfortable shorts didn’t necessarily result in the greatest protection from shock/vibration and the lowest perineal pressure.

One possible reason is that a slightly less comfy short insert encourages the cyclist to shift his/her weight around more and take more weight through the pedals rather than ‘sitting back’ on the saddle. So what are the best designs and materials for cycling short inserts to minimise perineal pressure? The truth is that no other studies have been carried out into this topic, so (despite the claims of manufacturers) we don’t really know.

Multi-factorial risks

Although a major factor, the risk of perineal injury is not solely due to saddle design. In a recent study on 2,774 male cyclists, researchers looked at all the contributing factors⁽⁸⁾. They found that there was a statistically significant increase in the risk of genital numbness with the following:

• More years of cycling
• More frequent weekly cycling
• Longer cycling distance at each ride
• Less frequent use of padded shorts
• Lower handlebar settings

The first three factors suggest a cumulative damage effect, which implies cyclists seeking to increase mileage/training volume need to take maximum precautions against perineal injury risk.

Road conditions may also be a factor in determining perineal injury risk. A 2018 study simulated the effect of riding on a smooth surface with no vertical oscillations, or with moderate and severe oscillations (mimicking bumpier road surfaces)⁽⁹⁾. It found that as the amount of oscillation increased from an average of 0.7G to 1.3G, the perineal pressure increased from 10.3% over baseline to 19.4% over baseline, and that there was a strong linear relationship between the amount of oscillation and increase in pressure. Interestingly, when the cyclists rode with a seatpost shock absorber (Suntour SP12-NCX Suspension Travel Seatpost), the impact of the oscillations was decreased by up to 53%. This suggests that shock-absorbing seatposts could help cyclists to reduce the risk of perineal injury, especially if they ride poor road surfaces!

Summary and practical advice

If you’re a cyclist, cycling coach/trainer, physician or clinician with cyclists in your care, what are the key points that should be born in mind to ensure maximum perineal health? Here are some guidelines:

• There’s no ‘best’ saddle – just the saddle that’s best for an individual’s anatomy. Cyclists should be prepared to try a few saddles until they’re happy they have one that works (most good local bike shops will have loan saddles cyclists can try for a week or so before going ahead with a purchase).
• Regardless of the amount of cushioning or presence/absence of V-grooves and cut outs, a wider saddle is likely to spread the load more evenly, reducing perineal pressure. This advice is especially relevant for female cyclists, who have wider spacing requirements for the sit bones.
• Saddle angle/height matters; a slight downwards tilt of just a couple of degrees can help reduce perineal pressure. Meanwhile, saddle height should not be excessive.
• Time trial and triathlon cyclists who do a lot of ‘aero’ riding should consider a ‘clipped-nose’ saddle (eg Adamo’s Podium saddle or Specialised’s S-works Power saddle), which reduces perineal pressure when the trunk is at a low angle.
• Cyclists who ride poor/bumpy road surfaces may benefit from a shock-absorbing seatpost (or switching to smoother tarmac). Experimenting with cycling short design may also be worthwhile; gel inserts are effective at absorbing vibration from the road, so may confer an advantage.
• Regardless of saddle comfort, cyclists should be encouraged NOT to sit in the same position for long periods. Getting out of the saddle for 20 seconds of so every few minutes can help relieve pressure on the perineal area and make for more comfortable riding. This is especially relevant when mileage/training times are being increased.

References

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