Choosing a suitable bicycle saddle can increase riding comfort and lengthen the cycling time. Previous research has shown that female cyclists have several reproductive health problems (Guess et al., 2011); thus, it is necessary to design bicycle saddles that can help overcome these problems. However, the largest width of a bicycle saddle currently available is 15.5 cm, which is reportedly uncomfortable for a long cycling time and is the main complaint regarding cycling (Chen and Liu, 2014). Cycling can cause pelvic floor pain, perineal numbness, abrasions, urethritis, and other diseases (Guess et al., 2006; 2011; Silbert et al., 1991; Weiss, 1994). Therefore, numerous improvements have been made to the design of bicycle saddles to mainly improve comfort and reduce the incidence of associated diseases. Currently, various saddle designs are available; several adjustments have been made on the incision and sponge filling of the saddle (Lowe et al., 2004). However, most studies have concentrated on improving the material of the bicycle, and few have focused on the influence of the human anatomy when designing a saddle.

At present, bicycle products and accessories have been mainly developed and designed to accommodate the anatomy of male cyclists, and the products are assumed to meet the needs of female cyclists when they are proportionally reduced in size without any further design and development. In addition, sex issues in different sports have recently garnered attention (Bury et al., 2020; Mitani, 2017; Phinyomark et al., 2016). For cycling, sports injuries occur more frequently in women than in men (Briggs and Obermire, 2016; Bury et al., 2020; Priego Quesada et al., 2019). Furthermore, women are twice more likely to develop patellofemoral pain syndrome than men (Boling et al., 2010). Some studies have shown that during exercise, women produce greater hip adduction and pronation and knee joint abduction than men, resulting in differences in lower limb kinetic and kinematic parameters (Ferber et al., 2003), which may be one of the factors causing patellofemoral pain syndrome (Willson et al., 2011). Therefore, adjusting bicycle designs according to the human limb can reduce the incidence of sports injuries (Encarnación-Martínez et al., 2020).

For the examination of riding comfort, a pressure saddle can be used to accurately record and evaluate the pressure distribution of the saddle during cycling (Holliday et al., 2019a) and observe the changes in pressure indexes, which may predict the occurrence of injuries (Vette et al., 2019). Pressure sensors are widely used in gait detection (Booth et al., 2020; Naderi et al., 2020; Yokozuka et al., 2020). Pressure parameters are important reference indexes to help identify and rectify the design of bicycle saddles (Bressel and Cronin, 2005). Previous research has shown that saddles with an incision affect the pelvic inclination angle and comfort of female cyclists (Bressel and Larson, 2003) and reduce the perineal pressure in male cyclists. Furthermore, when changing from holding the upper handles to the lower ones, men have smaller pressure peaks than do women, which may be due to the different distribution of the body mass between men and women, as the center of gravity of women is lower than that of men (Bressel and Cronin, 2005). According to previous studies on bicycle saddles, bicycle saddles should be designed considering the anatomical differences between sexes. When men and women sat in the same position on the same saddle, the width of the ischial tuberosity of women was greater than that of men (Chen, 2018). At present, the designs of bicycle saddles are still being improved to accommodate the needs of female cyclists, indicating that most cyclists are not satisfied with their bicycle saddles. Therefore, this study aimed to explore the influence of saddle widths on various pressure parameters in female cyclists. We hypothesized that a wider saddle would reduce the saddle pressure during cycling in women.

Ten healthy women were recruited for this study. These participants had an average age of 20.7 ± 1.3 years, height of 162 ± 5.9 cm, weight of 56.1 ± 7.5 kg, and a sciatic bone width of 15.5 ± 1.4 cm. Sample size calculations (G*Power, version 3.1.9.7) revealed that a sample of 10 participants would be sufficient to detect a difference according to the saddle width, with a statistical power of 0.98 and Type I error probability associated with the test of this null hypothesis, 0.05. They had no history of lower limb musculoskeletal injury or injury related to the neurological system during the year prior to the study. The participants provided their informed consent prior to the experiment. The study was approved by the Institutional Review Board and was conducted in accordance with the principles of the World Medical Association Declaration of Helsinki.

The saddle pressure mat used in this study has been extensively used by other studies, in which the reliability and validity has been determined (Bressel and Cronin, 2005; Swart and Holliday, 2019). The pressure saddle sensing system was used for all tests at a frequency of 200 Hz. The system consisted of a thin saddle containing 64 square capacitive pressure sensors (7.09 × 7.09 mm) mounted on the saddle, which was calibrated according to the manufacturer’s instructions. The GebioMized system recorded the following parameters: maximum pressure, mean pressure, pressure area, pressure front/rear, pressure left/right, maximum force, and mean force (Figure 1).

Four different saddle widths (i.e., 14 cm, 15 cm, 16 cm, and 17 cm) were tested. Each saddle weighed approximately 600 g (Figure 2) and was made of polylactic acid using a three-dimensional printing machine. The saddle bracket was made of steel. A thick high-density sponge was used to soften the saddle surface to imitate commercially available saddles. Participants whose width of the ischium was 13 cm or 14 cm were excluded from this study.

For minimal experimental error, the same bike model was ridden by all participants throughout the experiment to exclude the potential influence of different bike frame geometry that might result in changes in riding postures. The saddle height was adjusted until the knee flexion angle reached 30 degrees when the crank was at the 6 o’clock position. Previous research has shown that this posture configuration is beneficial and exerts less stress on the knees, which reduces the incidence of knee and thigh injuries (Swart and Holliday, 2019). Furthermore, the trunk flexion angle remained constant at 45 degrees in this study. Cyclists are recommended to maintain an upright riding posture when riding as it is more comfortable (Priego Quesada et al., 2017). Likewise, participants in this study were instructed to maintain an upright riding posture while holding the upper handles of the bicycle. This riding posture has been previously found to reach a higher ecological validity (Kordi et al., 2019).

Upon the arrival of the participants at the laboratory, the experimental procedures were first explained to them. Once an informed consent was obtained, the participants’ body and limb segments were measured to determine the suitable saddle. In this study, the saddle with an equivalent length to the participant’s ischium width was defined as moderate, while those with a length greater or less by 1 cm were defined as wide and narrow, respectively. The participants also chose a saddle that was considered comfortable for them, and the same researcher installed the pressure saddle on these self-chosen saddles to minimize errors. Before cycling, the participants warmed up for 10 min, and after the installation, saddles with different widths were tested using the counter-balancing method to minimize random errors caused by adaptation or the study design. During the test, the frequency of pedaling and the output voltage were observed using the Giant POWER PRO power meter, and the participants were not informed when data were recorded, to prevent them from changing their pedaling actions. They cycled at 100 watts at 90 rev·min^-1 and 10 min each time. Stable pedaling for 30 s was recorded, and the participants rested for 5 min between different experimental conditions.

The GebioMized system recorded the pressure parameters (Figure 1), and all values are presented as mean ± standard deviation for subsequent statistical analysis.

The SPSS software (Version 22.0, IBM Corp., Armonk, NY, USA) was used for statistical analysis. One-way repeated measures ANOVA was used to compare the influence of saddle widths on pressure parameters. According to the square value of net correlation Eta (η2), the effect size was determined. The degree of effect size was defined as follows: 0.01–0.06 = small, 0.06–0.14 = moderate, and > 0.14 = large (Cohen, 1988). When the main effect size was significant, the Bonferroni method was used for post-hoc test comparison. The significance level was set at α = 0.05.

One-way repeated measures ANOVA showed that there were significant differences in the maximum rear left sit bone pressure, maximum rear right sit bone pressure, mean rear right sit bone pressure, pubic pressure area, rear right sit bone pressure area, and mean force when different saddle widths were used. However, the maximum pubic pressure, mean pubic pressure, mean rear left sit bone pressure, rear left sit bone pressure area, longitudinal pressure, transverse pressure, and maximum force did not show any significant differences (Table 1).

Based on the post-hoc comparison, the maximum rear right sit bone pressure on wide saddles was lower than that on narrow (p = 0.001) and moderate (p = 0.016) saddles, and the mean rear right sit bone pressure on wide saddles was lower than that on narrow (p = 0.012) and moderate (p = 0.019) saddles. The pubic pressure area for wide saddles was smaller than that for narrow (p = 0.005) and moderate (p = 0.018) saddles, and the rear right sit bone pressure area for wide saddles was larger than that for narrow (p = 0.017) and moderate (p = 0.036) saddles. The mean force for moderate saddles was greater than that for wide (p = 0.008) and self-chosen (p = 0.025) saddles.

This study investigated the saddle pressure of different saddle widths (i.e., narrow, moderate, wide, and self-chosen). Our results showed that changing the saddle width affected the saddle pressure, and the hypothesis of this study was accepted.

In this study, we determined the optimal saddle width for women based on the width of the participants’ ischium and found that increasing the bicycle saddle width by 1 cm according to the width of the participants’ ischium effectively reduced the maximum and mean pressures of the saddle. This might be due to the dispersion of the maximum and mean pressures by an increase in the pressure area. The results of this study are similar to those reported in previous studies. Different saddle widths provide different pressure distributions, and the results are affected by the pelvic size and area in contact with the saddle (Chen, 2018; Potter et al., 2008). For comfort, the saddle should be widened to provide better support for the ischium (Chen, 2018). However, previous studies did not describe a clear method for choosing a bicycle saddle.

Many cyclists have pointed out that long-term use of regular bicycle saddles causes pubic pain, as they are not designed based on the pelvic anatomy (Keytel and Noakes, 2002). In addition to having differences in the sciatic width, which is measured externally, men and women also differ in terms of internal structures, including the pubic tubercle width, pubic arch angle, and location of the pubic symphysis (Potter et al., 2008). The pubic tubercle is wider in women than in men, and the pubic arch angle in women is greater than 90 degrees while that in men is less than 90 degrees (Chen, 2018). The locations of the pubic symphysis in men and women are 116.5 mm and 134.9 mm (Sauer et al., 2007), respectively, with a difference of 14.0–18.4 mm (Chen and Yang, 2016). However, at present, the saddles for women are wide r than those for men (i.e., 150 mm vs 130 mm, respectively). Nevertheless, this study found that the average saddle width suitable for women is 160 mm. This width is speculated to improve the saddle pressure during cycling. Incorrect saddle designs do not effectively disperse the weight and reduce the stress, thus increasing the risk of injuries (Andersen and Bovim, 1997; Keytel and Noakes, 2002; Schrader et al., 2002).

This study aimed to explore the saddle pressure of different saddle widths. For reduced experimental errors, only the width of the saddle varied, while other variables remained constant. However, other factors might influence out study results (Bressel et al., 2009). Previous research has indicated that riding comfort and stability vary with time, and that the mean pressure of the saddle increases with an increase in the pedaling load (Holliday et al., 2019a). However, in this study, the experimental time was the same for all participants.

There is bilateral asymmetry when running and riding bicycles, which increases the risk of injury (Carpes et al., 2010). In our study, there were significant differences in the maximum pressure, mean pressure, and pressure area on the rear right sit bone, but there was no difference on the rear left sit bone. Therefore, we speculate that the uneven pressure may be caused by asymmetric pedaling and can increase the incidence of injuries on the rear right sit bone. In addition, our results showed that using a wide saddle could reduce the asymmetric effect of the saddle pressure. Hence, a change in the saddle size might affect the pedaling symmetry (Figure 3).

It is possible to improve performance and reduce sports injuries by adjusting the bicycle posture (Holliday et al., 2019b). Recent research has shown that the same bicycle posture adjustment methods lead to different saddle heights and lower limb joint angles for men and women (Encarnación-Martínez et al., 2020). These differences are due to differences in the pelvic structures between sexes; notably, previous posture adjustment methods have been designed only for men (Silberman et al., 2005). Previous studies on saddle pressure investigated the differences between male and female cyclists (Bressel and Cronin, 2005; Bressel and Larson, 2003; Gordon, 1999) and found that the mean force and maximum pressure of the saddle shift forward for male cyclists and remains more concentrated in the center of the saddle and on both sides of the ischium for female cyclists. Potter et al. also showed that the pressure distribution in women during pedaling is concentrated on both sides of the ischium (Potter et al., 2008). These findings, along with our results, show that men and women experience different degrees of comfort even when the same saddle is used, and that there might be a greater risk of injury when an unsuitable saddle is used. Therefore, it is necessary to adjust the saddle size according to the width of the female cyclist’s ischium to accommodate the riding needs of female cyclists.

This study found that a saddle 1 cm wider than the cyclists’ ischium could improve the pressure distribution of the saddle during riding, thereby providing better comfort. In addition, the pressure is distributed more symmetrically when a wide saddle is used, which may improve the pedaling symmetry.