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Don’t be pressured: why hamstrings matter for cycling comfort
Saddle soreness can literally be a pain in the backside for cyclists. With that in mind, SPB looks at fascinating new research on the link between hamstring flexibility and saddle pressures when on the bike
One of the great appeals of cycling as an endurance sport is that the risk of injury is relatively low, especially when compared to sports such as running. Research on triathletes (who engage in both disciplines) has found that running injuries are 3-5 times more frequent as a result of running compared to cycling(1). This is perhaps unsurprising because the smooth, impact-free and supported nature of the pedaling action makes cyclist less vulnerable to impact injuries or those cause by faulty biomechanics. Having said that, cyclists can and do suffer injuries from their sport.
Interface and injury
When a significant injury does occur in cyclists, the most common cause is likely the result of a collision or fall from the bike. Research on road cyclists shows that abrasions, lacerations and bruises as a result of a fall/collision accounted for around half of the total injuries recorded. Meanwhile, fractures (6-15%) were the second most frequent type of injury, with knee pain being the number one overuse diagnosis. The riding posture maintained for long periods of time can also result in back pain, especially when the handlebars are set low (see this article).
What’s often overlooked when considering injury however is the bike-rider interface. With the body weight supported on a narrow saddle and (to a lesser extent) the handlebars, plus constant force being applied through the pedals, these three contact points have the potential to produce injuries, especially when training volumes are high. And of those three interfaces, the greatest sustained forces are 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) 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.
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. 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(2). In around 20% of male 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).
Pelvic posture and saddle pressure
Given that the greatest forces at the three contact points are applied through the saddle, it’s not surprising that saddle design has been well researched by sports scientists and bike manufacturers alike. Design features such as saddle width, cushioning and whether or not it has a groove or cut out under the perineal area have a big impact on the forces experienced by cyclists, and can make all the difference between a saddle that is agony to ride after 30 minutes and one that can be ridden for hours on end with no ill effects (see this article). However, the actual loading experienced at the saddle-bum interface also depends on the position of the rider’s pelvis – in particular the degree of forwards-backwards tilt(3).
It’s known that the flexibility of the hamstring muscles affects pelvic posture in terms of backwards-forwards tilt. The hamstring muscles attach to the base of the pelvis (via the ischial tuberosity), and looking at figure 1, we can see that shortened hamstring muscles of the rear thigh will act to pull on and rotate the pelvis in a backwards direction (B in the figure). This effect has been confirmed in previous studies, which have shown that reduced hamstring flexibility rotates the pelvis posteriorly(4,5). This can reduce the pelvis’s ability to move properly during lifting movements, thus hampering the lower spine in its effect to adopt its natural curve, which increases the forces on spinal ligaments and discs, thus increasing the risk of back injury.
If the pelvis tilts in response to hamstring flexibility/tightness and the angle of the pelvis influences how a cyclist sits on the saddle, a good question to ask is whether pelvic tilt can influence the distribution of saddle pressures? In particular, what are the effects of tight hamstrings and/or lower back muscles on the pressure distribution while seated on the saddle, and could hamstring flexibility play a role in determining whether cyclists suffer from saddle soreness?
Figure 1: Anterior and posterior pelvic tilt
New research
For answers, we can turn to a brand new study by a team of Italian scientists based at the University of Palermo, Italy(6). Published in the journal ‘Frontiers in Sport and Active Living’, this study set out to investigate whether the flexibility of hamstring and lower back muscles could be considered a predictor of pressures in the anterior (nose) region of the saddle, and by implication, whether increasing hamstring flexibility might help cyclists who suffer from saddle soreness. For this study, 15 young off-road Italian cyclists (11 males and 4 females) aged 13–16 were recruited. All had been mountain biking for at least two years and training for at least three hours per week during that time. Exclusion criteria were that the cyclists had no previous history of saddle sores or skin irritations in the perineal area, no history of perineal numbness and no musculoskeletal injuries in the previous six months.
What they did
Prior to a cycling trial, each participant was administered the ‘V sit-and-reach’ test to measure the flexibility of hamstrings and lower back muscles. In this test, each participant was seated on the floor with the lower limbs extended, feet spaced 30 cm apart, and the base of the feet touching a box to keep the ankle joints in a neutral position(7). Participants were asked to keep their upper limbs extended, flex their trunk, and reach as far as possible sliding the hands along the floor. Three trials were performed, and the distance reached (in centimetres) in the third trial was measured.
Each participant was then evaluated on their own bike while riding on a bike roller (MagneticDays; Foiano della Chiana, Arezzo, Italy). Before riding, each cyclist’s bike set up was adjusted, with the aim of optimizing the posture and biomechanical efficiency of each participant. Following this, each participant was asked to warm-up for 10 minutes at a self-selected pedaling cadence and intensity. Then, a flexible mat, composed of resistive sensors capable of recording saddle pressures was placed on a sex-neutral saddle (Selle Italia S1). This allowed the researchers to obtain a ‘pressure map’ to find out which areas of the saddle interface experienced the most pressure (see figure 2). Subsequently, the saddle pressures during pedaling at three different intensities (100W, 140W, 180W) were recorded at a pedalling cadence of 90rpm. Each trial lasted 30 seconds with a 3-minute rest between the three intensity trials.
Figure 2: Pressure map obtained from a rider/saddle interface
What they found
The results were very clear cut; at all three of the cycling intensities, higher scores in the hamstring/lower back flexibility test were correlated with lower saddle pressures in the front region of the saddle (ie the perineal area). As figure 3 shows, this relationship was fairly linear, with the same pattern for all three cycling intensities. These finding clearly indicated that hamstring flexibility can and does affect the saddle pressure experienced by cyclists.
Figure 3: Hamstring flexibility score and saddle pressures in the perineal region
Implications for cyclists
If saddle comfort in the groin area is something that you struggle with - even after trying out different saddle designs - improving your hamstring flexibility is definitely a worthwhile strategy to explore. That because your pelvic position/tilt plays a key role in the distribution of pressures you will experience in the saddle. The kind of stretching that is best for developing hamstring flexibility is slow, static stretches held for 15-30 seconds. There are many ways of stretching your hamstrings, but some (eg the hurdler stretch) can place undue stress on the lower back and may even result in injury. If you want to improve your hamstring flexibility safely, a great place to start is with the stretches outlined in the excellent ‘Bob and Brad’ video (link below).
www.youtube.com/watch?v=setNNb-JK6Q
In addition, there are a few other tips worth bearing in mind when seeking maximum saddle comfort. These are as follows:
- There’s no ‘best’ saddle – just the saddle that’s best for your anatomy. Be prepared to try a few saddles until you’re happy you 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, 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
1. J Sport Health Sci. 2023 Mar 8;13(2):172–185
2. Eur Urol. 2005 Mar;47(3):277-86
3. Spine (Phila Pa 1976). (2010) 35:E1193–1198
4. Int J Ind Ergon. (2009) 39:115–20
5. J Back Musculoskelet Rehabil. (2012) 25:161–9
6. Front Sports Act Living. 2024 Oct 17;6:1472550. doi: 10.3389/fspor.2024.1472550
7. J Sci Med Sport. (2007) 10:456–62
Andrew Hamilton
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