ASSESSING THE IMPACT OF THE INTRINSIC CHARACTERISTICS OF SEAT-PADS ON COMFORT AND PERFORMANCE
article by Romain Raitano and Nicolas Gregoire
Comfort denotes a situation, gesture or position in which the subject feels a general state of well-being.
Comfort is often contrasted with performance, since both concepts appear to be literally and biomechanically divergent. However, as demonstrated by our previous article, entitled ‘A closer look at clothing characteristics for changing weather conditions’, comfort on the bike is not only essential for achieving pleasure, but also for deriving maximum benefit from the cyclist’s physical capacities. In top-level sport, the smallest details sometimes make all the difference, and the level of comfort will help increase the cyclist’s endurance and ability to endure pain.
Because the notion of comfort depends primarily on the individual, it would seem difficult to find a one-size-fits-all solution. Nevertheless, in the case of cycling and more specifically the interface between cyclist and saddle, studies have shown correlations between the subjective notion of comfort and objective factors that can be measured in the laboratory.
Chamois pads appeared at a time when constraints were prompting efforts to improve comfort.
Today, actual chamois pads are a collector’s item (see Figure 1), not unlike an old pair of skis. Since shorts were worn without any underwear, the original aim was to prevent friction burns, and chamois pads are recognised for their anti-abrasive qualities. Over the years, pads have seen their list of attributes grow even longer, such as the appearance of foam to “soften” the sitting position. Chamois have since become a protected species, which has encouraged the development of synthetic materials that also herald new technical possibilities, including moisture management, improved breathability and superior load-bearing capacity.
“Chamois pads” today play a decisive role. They need to maximise the cyclist’s comfort without deteriorating performance, while sometimes even indirectly improving performance.
Understanding the challenges facing the development of a cycling pad requires an insight into the man-material-environment triptych. Each component in the triptych will have an influence on the others, and vice versa. The parameters relating to the cyclist will influence the pad (material), while the environment will influence the material’s behaviour.
The aim in drawing up a list of parameters for each component in the triptych is to identify the objective notions underlying comfort (see Figure 2).
Figure 2 Cyclist-Material-Environment triptych
Since the cyclist’s parameters are hard to adjust or even unchangeable, which is also true of the environmental conditions, the pad needs to adapt to the requirements of the other two components. The pad features a specific thickness and construction to suit the cyclist’s weight, which varies from one individual to another, and from one sex to another. In hot or cold conditions, the cyclist’s perspiration rate will vary, meaning that the pad will have to adapt accordingly.
In order to gain an insight into the constraints relating to the cyclist-saddle interface, Mavic’s research and development teams have pioneered a series of tests, ranging from highly theoretical lab-based tests through to testing under real conditions. Knowing and understanding these parameters will help develop products that are geared towards the cyclist, the environment and cycling conditions.
1. Laboratory tests: measurement of anthropometric parameters
Before any mention can be made of foam quality, the actual position of the foam is critical. It is all very well having the best complex foam pad in the world, but if it is poorly positioned, it will be useless and may even exacerbate the situation by causing discomfort zones.
To ensure that the foam pad is correctly positioned, an in-depth analysis of the cyclist-saddle interface is required. How is the cyclist seated on the saddle? When sitting on the saddle, what is the cyclist resting on? To provide a suitable answer to this question without merely replying “I’m sitting on my backside”, knowledge of the anatomy of the pelvis is necessary (see Figure 3). When sitting vertically, we are actually resting on the ischial tuberosities. The same applies when sitting on a bike saddle. These points will therefore be key to the position of the foam pad.
Figure 3 Articulation of the human pelvis
The same applies when sitting on a bike saddle. These points will therefore be key to the position of the foam pad.
The subject’s height and sex are anthropological factors that lead to different distances between the ischial tuberosities. That is why Mavic’s development teams carried out a measurement campaign on a large sample of men and women for the purpose of evaluating this measurement. Researchers developed a simple tool for effectively measuring the mean distance between the ischial tuberosities, as well as the standard deviations between individuals.
Results show that women’s inter-ischial distance is significantly greater than men by 16.7% (see Figure 4).
Figure 4 Ischial width according to sex
Furthermore, due to the specific position that cyclists adopt when sitting on the saddle, meaning leaning forward, the body’s weight is not only resting upon the ischial tuberosities, but the entire pubic bone. Once again, the anthropometric measurements taken highlighted a significant difference between men and women. In women, the pubic bone forms an arch between the ischial tuberosities and the pubis. The cyclist’s weight is therefore supported by three distinct points: the two ischial tuberosities and the pubis. In men, the pubic bone is straight, which results in the weight being supported by a point shaped like an upside-down V.
Consequently, with some simple measurements, cycling pad quality can already be improved by strategically positioning the foam. Thanks to Gauss’s law, or the “normal distribution” as it is called, these results can be generalised to produce pad dimensions suited to over 95% of the population (see Figure 5).
Figure 5 Population distribution in terms of the ischial width in men
This study into the inter-ischial distance can therefore be used to determine where and how to position foam pads according to anatomical criteria. Other mechanical criteria, such as a cyclist’s weight and road surface type, will also influence the interaction between the cyclist and the pad. New tests have been developed to evaluate how foam reacts to these parameters.
2. Laboratory tests: measurement of mechanical qualities
The samples tested are simple or complex foam pads with identical diameters of 42 mm (see Figure 6). The thickness may vary, but the results will always be expressed in relation to the same reference.
Figure 6 Typical foam sample
Rebound test
The rebound test involves striking the foam sample with a hammer fixed to a pendulum (see Figure 7). An accelerometer is attached to the hammer and measures the rate of change of velocity according to time.
Figure 7 Principle and photo of the rebound test
This test is used to quantify two parameters: deceleration and resilience.
Figure 8 Typical results of shock absorption measurements (deceleration) according to the type of pad
E_(before impact)-E_(after impact)=E_released%
An optimal value is required for cycling pads. Above all, the value must not be too high, otherwise cyclists would bounce off the pad like a trampoline. Furthermore, overly resilient materials would increase the transmission of vibrations, which is undesirable. A low resilience value should also be avoided, since if a force is applied to the saddle, such as the force associated with the propulsion required for pedalling, it would hardly be transmitted or even not at all. Resilience and load-bearing capacity are positively correlated (if one increases, so does the other, and vice versa). Achieving an optimal value is therefore important for reducing vibrations while maintaining effective propulsion.
Vibration tests
Vibration tests are carried out at the same time as the rebound test for the purpose of minimising vibrations. In terms of the cyclist-saddle interface, vibrations are harmful to the cyclist’s performance, comfort and health. Muscles are stimulated by electrical currents. As such, the more the brain sends a “current” to the muscle, the greater the stimulation and the higher the force generated. Studies have shown that vibrations over-stimulate muscles, meaning that for the same effort, a muscle needs greater stimulation (more “current”) to contract. This is due to the need to “control” vibrations, which therefore causes the cyclist to waste energy. Furthermore, such vibrations disrupt the body’s spatial perception and may lead to vascular disorders and the “pins and needles” sensation. Basically, the cycling pad must also smooth out vibrations to reduce such disruptive factors.
Before starting the tests, Mavic’s research team had to take a series of measurements on the different frequencies of the vibrations at the cyclist-saddle interface under real conditions. By placing an accelerometer at strategic points, testers were able to record the vibration frequencies generated in a maximum number of real conditions according to the state of the road surface, speed and type of material used (carbon or aluminium wheels, for example), and so on.
The vibration frequencies were then reproduced with a vibrating platform. Using an accelerometer placed on top of a weight representing the cyclist, the ability of the different foam samples to smooth out vibrations was evaluated (see Figure 9).
Figure 9 Diagram of the vibration test on a vibrating platform
Mavic’s teams reviewed the quality of existing cycling pads based on this parameter (Mavic’s and competitors’ pads), and then determined the minimum acceptable values for new pads. Typical values can therefore be associated with different range levels (see Figure 10).
Figure 10 Typical results of the vibration test
The difference can clearly be seen with intermediate frequencies. All frequencies tested are those that were experienced out in the field under different cycling conditions.
To effectively understand the phenomenon of vibration absorption, imagine hitting a complex foam pad with a hammer (see Figure 11).
Figure 11
The vibrations will behave differently according to the complex construction. On the one hand, the amplitude of the vibration will vary. In other words, the higher the amplitude, the harder the perceived vibrations, and vice versa. On the other hand, the time required for the material to return to its “normal” state is also important. The longer the time, the more the subject will feel the vibrations. The opposite effect is therefore desired. The graphic below clearly expresses both concepts (see Figure 12).
Figure 12 Results of the “hammer impact” test according to the material
A gel-type material is thus compared to an OrthoLite® foam.
The red arrow indicates the material’s return to its normal state. The gel is not very effective at smoothing out vibrations, because the time required to return to its “normal” state is much longer than the OrthoLite® foam. Furthermore, the amplitude of the vibrations is much higher with the gel, which is undesirable.
Load-bearing test
After testing the capacity to absorb shocks and smooth out vibrations, Mavic’s team tested the pads’ ability to “support” the cyclist’s weight. The load-bearing test involves applying a force to compress the sample and then measuring the sample’s compression as a percentage (see Figure 13). This test determines the extent to which the pad will be compressed by the cyclist’s weight.
Figure 13 Load-bearing test
Once again, an optimal value is required: if the foam is excessively compressed, it will be “useless”. This would be akin to breaking through the foam, and the load-bearing value would actually correspond to the surface beneath the foam (i.e. the bike saddle). In case of low or non-existent compression, the foam would be too rigid and therefore uncomfortable, like sitting on concrete. The example below (see Figure 14) clearly illustrates the concept: both foam pads are compressed with an 80 N “weight” (a force). One compresses to 50% (right) while the other compresses to 70% (left). Therefore, it can be seen that the load-bearing capacity of the foam pad on the left is insufficient.
Figure 14 Typical results of a load-bearing test using an effective foam pad (right) and a poor-quality foam pad (left)
Breathability test
The previous tests are used to evaluate the ability of cycling pads to support the cyclist’s weight (load-bearing) and protect against the quality of the road surface (vibration and rebound). A key parameter has not yet been tested, namely the ambient climate and the moisture rate within the cycling pad. Thebreathability test involves measuring a material’s capacity to wick away moisture. To measure breathability, “wells” are filled with a specific and constant quantity of water for each test (see Figure 15).
Figure 15 Breathability test well
The material being tested is positioned to cover the well. The result expresses the quantity of water that has evaporated and the time required for evaporation. As with bib short fabrics, cycling pads need to effectively wick away perspiration and moisture. The cyclist-saddle interface is a special area, insofar as sitting on the saddle creates a “closed” atmosphere, which affects the short’s breathability in this particular area. Furthermore, the different layers of foam and the adhesive used are parameters that also prevent breathability.
Ultimately, this is an area where moisture management is essential. For this test, the development teams defined the minimum value for moisture wicking. Any pads beneath the threshold value were invalidated and redesigned. In addition, the threshold value increases according to the range level.
In order to reproduce real cycling conditions as accurately as possible, all laboratory tests are systematically carried out under many different conditions. For example, in case of breathability tests, the hygrometric data (i.e. temperature and relative humidity) are checked. For load-bearing tests, the surface area of the samples used is much smaller than a full cycling pad. That is the reason for which the force applied is weighted in relation to the actual surface area.
Each material and each complex is tested twice or even three times after a fatigue simulation. By compressing the samples at a specific frequency (consistent with cycling) and with a given force over a specific duration or number of cycles, Mavic’s R&D teams can cause “fatigue” in the materials and then test them again. This method enables them to determine the service life of materials, complexes and cycling pads.
Thanks to these tests, Mavic’s development teams were able to evaluate each foam pad independently of the others, whether using pads from Mavic’s suppliers or new materials with seemingly interesting properties. Pads were combined to create bi-density and even tri-density complexes for the purpose of enhancing their qualities.
Each complex, whether old or new, is evaluated using this series of tests. Cycling pads are therefore subjected to a stringent set of specifications in terms of required results before moving onto the second test phase: field testing.
In-situ or field tests
Field tests are sometimes difficult to perform, simply because measuring instruments are not “portable” or may cause the subject discomfort. A number of biases are also involved. Based on a surface pressureanalysis, Mavic’s development teams found a test for objectively translating the notion of comfort without impeding the cyclist’s movement or requiring large equipment (see Figure 16).
Figure 16 Subject during a pressure test
The pressure level is negatively correlated to the sensation of comfort, meaning that the higher the pressure, the more the cyclist experiences discomfort. This discomfort, which is felt by the cyclist in the short and medium term, is caused by the compressed fabrics at the cyclist-saddle interface. In the long term, constant and repeated compression may lead to a number of problems relating to reduced blood flow and pinched nerves: erectile dysfunction in men, priapism, penile thrombosis, infertility, haematuria (blood in the urine), numbness, regular and prolonged loss of sensation and ultimately tissue necrosis.
The results of the pressure test are consequently important, especially since the test is carried out in near real conditions.
Pressure sensors are placed on the saddle. For each cycling pad, data were recorded under different conditions, such as pedalling frequency, power and position.
The results were analysed on a computer to produce a map of the distribution in pressure and the level (see Figure 17). Visually, high pressure is represented by hot colours (yellow, red and black). The objective is to eliminate peak pressure levels throughout the duration of the cycle and achieve the lowest possible average pressure.
Once again, threshold values were defined, based on which cycling pads were approved or invalidated.
Figure 17 Typical distribution in pressure during the downstroke with the right leg
At the same time, subjective tests were carried out. Although objective data can be correlated to comfort, the subjective feeling is nevertheless important.
Mavic uses its own panel of testers, from touring cyclists to professional racers. Each member is given a series of pads to be tested according to the conditions defined by the development team (session time, distance, weather conditions, etc.). They are given a questionnaire that enables the tester to evaluate the degree of comfort according to various criteria, including moisture management, friction and perceived comfort at the front and back of the pad.
The results (see Figure 18) are used to approve or invalidate the pads tested, as well as incorporate the testers’ impressions. Each comment is taken into account at all times during the development stage. Each idea is analysed to consistently improve the bib shorts under development.
Figure 18 Typical results of the subjective evaluation of a cycling pad (non-exhaustive criteria)
3. An ideal solution?
The research and development methods used by Mavic’s teams are aimed at identifying a maximum number of parameters that exist under real conditions, understanding their influence on comfort and performance, and reproducing them under controlled conditions during laboratory or field tests. All of these parameters are ultimately intended to answer the following question: What is the best cycling pad? Which one should you choose?
Because every person is different and because each ride is unique, the idea of a cycling pad designed to perfectly suit every situation is a pipe dream. Therefore, there is not one but many solutions responding to several types of parameters.
Ride profile
We will now take a look at the ride profile. You should not use the same cycling pad if you are racing on a track (or a perfectly asphalted road) or competing in the Paris-Roubaix race (or riding on a poorly-maintained road). In the first case, you should choose a “performance”-rated pad, i.e. a cycling pad offering a good load-bearing value (a firm pad) and optimal resilience, and which does not need to absorb shocks. This pad should maximise force transmission and especially minimise any restriction to the cyclist’s movement. The cyclist should therefore choose a pad with a minimalist design. For example, the Ergo 3D Pro insert will suit this ride profile. In the second case, the cyclist will need a pad with advanced vibration and shock-absorbing qualities. Force transmission will be less effective than minimalist pads, but the increased comfort will equate to superior performance in the long term. In this case, the cyclist should choose the Ergo 3D Endurance insert.
Duration
Duration is an important selection criterion. During a short ride, the average power developed is greater than during a long ride. As such, the cyclist will place a lot less “load” on the saddle, meaning that less force will be applied to the pad. In this case, a more minimalist pad should be prioritised. Furthermore, on short rides lasting from one to two hours, it is easier to endure the discomfort. If you are embarking on a long or very long ride lasting five to six hours or more, comfort is vital. Vibrations will be constant, shocks will be regular, and tissue will be compressed over an extended period of time leading to numbness.
Basically, the pad needs to be thicker and contain high load-bearing materials capable of smoothing out vibrations and absorbing shocks. The design must also be more forgiving, meaning that the pad needs to be wider so that the cyclist can move about on the saddle and change position. Furthermore, the pad’s “endurance” is important. It must not lose its qualities before the ride has finished. In the Mavic range, the Ergo 3D Endurance insert has been masterminded in response to these particular constraints, while the Ergo 3D Pro insert has been designed with shorter races in mind.
Sex
The pad should also be chosen to suit the individual. Although nowadays it may seem obvious to choose a woman’s bib short if you are a woman, it has not always been the case. Since the development of specific women’s products has not always been given the same priority as men’s products, women tended to choose men’s bib shorts. Unfortunately, this is a mistake that should be avoided. As we saw earlier, the anatomy of the pelvis in men and women is significantly different. The distribution of materials in a man’s pad is narrower than in a woman’s pad due to the distance between the ischial tuberosities. Despite being of a smaller build than a man, a woman’s ischial tuberosities would lie outside the protective areas of a man’s pad.
The level of proficiency and type of cycling must also be taken into account when choosing a pad. “Leisure” cyclists should choose a comfortable pad. Conversely, minimalist pads are the answer for cyclists in search of pure performance. Once again, the key is striking the right balance between performance and comfort.
Height and mass
Height and mass must influence the choice of pad. The correlation between the cyclist’s height and ischial width may be low, but it exists nonetheless. Exceedingly tall cyclists (over 2 m) should choose a wider pad, because they are statistically more likely to have a larger inter-ischial distance. However, the distribution and design of Mavic’s pads cover 99% of all ischial widths. The cyclist’s mass will influence the force (weight) applied to the pad. The greater the mass, the more the cyclist should focus on a thicker load-bearing pad. In addition, since there is a strong correlation between mass and height, it is in tall cyclists’ best interest to choose a load-bearing pad.
This is what racers think about when choosing their pad. Cyclists need to strike the right balance between their need for performance and their need for comfort. Here are two tangible examples for applying the above selection criteria:
Nicolas Roux, who completed the 334 km Tour du Mont Blanc in an astonishing 12 hours and 13 minutes with the same bib short, is a different example. Since his goal was performance, he obviously chose a pad allowing for efficient transmission of power, while guaranteeing a sufficient level of comfort to maintain maximum performance until the end.
In both cases, comfort invariably and indirectly acts as a driving force for performance.
This is actually an important point during the development phase for Mavic. Any high-end pad should enable the cyclist to comfortably ride 100 km or more. This gives cyclists a chance to also take account of pleasure and personal comfort when buying a bib short.
On more “extreme” rides, it is essential to “weigh up” the balance between performance and comfort. This involves cyclists identifying their own ride profiles. They should therefore test several pads: one pad for each type of ride profile.
4. Conclusion
Developing a high-quality cycling pad is therefore a highly complex process that involves finding the sweet spot from a number of parameters. Achieving that sweet spot means objectively assessing the intrinsic characteristics of the inserts and accurately measuring the conditions actually experienced during a ride in order to select the solutions offering the best response to a given set of parameters. For example, a men’s Endurance insert may suit extended rides as well as rides on poorly-maintained roads. Ultimately, performance needs to be validated with cyclists in real conditions. This line of reasoning actually applies to the development of many other products, such as tyres. In the end, such developments are always based on a combination of lab tests, field tests and tests with end users. However, perceived comfort remains highly subjective, and there is no guarantee that the same solution will suit different people.
http://www.engineerstalk.mavic.com/assessing-the-impact-of-the-intrinsic-characteristics-of-seat-pads-on-comfort-and-performance/
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