INTERNATIONAL JOURNAL OF IMPOTENCE RESEARCH
December 2002, Volume 14, Number 6, Pages 513-517
Purpose
The purpose of this study was to evaluate the effect of bicycle saddle shape on penile blood flow during cycling. Penile blood flow was measured using a laser Doppler flowmeter in 20 potent male volunteers. In a counterbalanced, crossover design, measurements were taken in the standing and sitting positions, on either a narrow unpadded or wide unpadded saddle, before and after cycling for 5 min. Before cycling, penile blood flow (ml/min/100 g tissue) was significantly decreased from 1.6±0.7 to 1.5±0.7 (P=0.010) on the wide saddle and from 1.7±0.6 to 1.0±0.5 (P<0.001) on the narrow saddle. After 5 min of cycling, the changes in penile blood flow on the wide and narrow saddles were 0.34±0.49 and -0.38±0.49, respectively (P<0.001). The narrow saddle is associated with more significant reductions in penile blood flow and could be a source of blunt perineal trauma, potentially leading to erectile dysfunction.
Introduction
Evidence, in the form of anecdotal evidence, case reports and questionnaire-based studies, has accumulated on patients who exercise on bicycles and complain of impotence or erectile dysfunction. In light of the popularity of cycling as a fitness activity as well as a competitive sport, the potential impact of cycling as an etiological factor in the development of erectile dysfunction is significant. However, relatively little attention has been devoted to elucidating the specific relationship between cycling and erectile dysfunction or the relevant pathophysiology.
It has been proposed that the bicycle saddle might affect penile blood flow during cycling.1 Genital numbness and impotence have been reported in some long-distance bicycle riders,2 and blunt trauma to the corpora cavernosa has been considered to be a risk factor for the subsequent development of erectile dysfunction.1,3,4 It seems that anatomical considerations of the structures compressed by the load placed on the bicycle saddle might explain the development of such symptoms. Furthermore, current bicycle saddle designs may be responsible for chronic injury to the perineum and thus may pose as a risk factor for erectile dysfunction.
Some previously published, questionnaire-based studies2 and case reports5 have reiterated many of the typical clinical symptoms. Very few studies, however, reported direct measurements of blood flow in the flaccid penis during cycling.
The purpose of this study was to investigate the relationship between the shape of the bicycle saddle and penile blood flow during cycling using laser Doppler flowmetry.
Materials and methods
A total of 20 healthy, potent, male volunteers (mean age, 23 y; range, 20-26) participated in this study. All subjects underwent routine evaluation for impotence. All were free of any clinical history of impotence, had no remarkable findings on routine blood profiles, and had no history of diabetes, Peyronie's disease or vascular disease.
In a counterbalanced, crossover design, all participants rode the same ergometer, while only the saddle was changed between an unpadded narrow type and an unpadded wide type. Baseline penile blood flow was measured in the standing position before beginning cycling. The effect of the bicycle saddle was assessed by measuring the penile blood flow in the seated position before and after cycling for 5 min on each saddle. Pedaling resistance was held constant for all subjects, and the participants were instructed to pedal at 40 rpm while remaining seated throughout the 5 min period. The volunteer was allowed to rest for 5-10 min between the two types of saddles.
The bike saddles used in this study are pictured in Figure 1. The transverse diameters at the widest points were 14 and 26 cm for the narrow and wide saddles, respectively. Both were constructed of the same materials and were assumed to vary only in terms of the surface area available for distribution of weight. As illustrated in Figure 1, the narrow saddle shares the typical piriform shape seen in commercially available narrow saddles. The wide saddle is more heart-shaped.
Penile blood flow was measured using a laser Doppler flowmeter (Transonic Systems Inc., Ithaca, NY, USA). A surface-type flow probe was placed on the glans penis and was held in place using adhesive tape. The flow probe was connected to the laser Doppler flowmeter, which was calibrated against an internal standard. Readings of blood flow were in units of ml/min/100 g tissue.
Penile blood flow measurements were taken in the standing and sitting positions just prior to beginning exercise and immediately upon cessation of exercise. All measured values and calculated values are reported as mean±s.d. in units of ml/min/100 g tissue. Disparities in effect of postural change (sitting or standing) and cycling (before and after) were determined by calculating the changes in blood flow. The effect of postural change is expressed as the difference between sitting and standing values on a given saddle. The effect of exercise is expressed as the difference between post- and pre-exercise values in a single position (seated or standing). Significant differences between means were identified from values determined by the paired t-test. Differences were considered statistically significant for a two-tailed hypothesis (P<0.05). Statistical analyses were performed using SPSS 10.1 (Chicago, IL, USA)
Results
Trends in alterations of penile blood flow were similar on both saddles with respect to position. At a given time point, the simple act of sitting on either type of saddle significantly reduced penile blood flow below baseline values, while blood flow significantly increased with cycling. However, the two types of bicycle saddles affected penile blood flow differently in that sitting on the narrow saddle caused significantly greater reductions in blood flow than on the wide saddle both before and after cycling (P<0.001 in both). Penile blood flow after cycling in the seated position on the narrow saddle was the only post-cycling condition in which the blood flow decreased below the baseline value.
Baseline penile blood flow measurements (in ml/min/100 g tissue) were arbitrarily defined as those recorded while standing prior to bicycling. They were recorded with the subject standing erect with a flaccid penis. There was no statistically significant difference in the baseline values of subjects using either the wide or narrow saddles (1.6±0.7 and 1.7±0.6, respectively).
Penile blood flow was significantly decreased by simply sitting on the saddle from 1.6±0.7 to 1.5±0.7 on the wide saddle (P=0.010) and from 1.7±0.6 to 1.0±0.5 on the narrow saddle (P< 0.001). The mean changes in penile blood flow prior to exercise by sitting on the wide and narrow saddles were -0.12±0.19 and -0.68± 0.47, respectively. Sitting on the narrow saddle resulted in significantly greater reductions in penile blood flow (P<0.001).
When the penile blood flow was measured with the subject seated on the saddle after 5 min of bicycling, the blood flows were 1.9±0.9 and 1.3±0.5 on the wide and narrow saddles, respectively (P=0.009, P<0.001 vs baseline, respectively). The decrease in blood flow on either saddle proved to be significant when compared both to the respective post-exercise standing values and baseline values (P=0.001, P<0.001 vs standing after exercise, respectively). Also, the decrease in blood flow resulting from sitting on the narrow saddle was significantly greater than on the wide saddle (-0.84±0.66 vs -0.19±0.21, P<0.001).
After 5 min of bicycling, penile blood flow significantly increased above baseline values to 2.1±0.9 and 2.2±0.9 in the wide and narrow saddles, respectively (P<0.001, P=0.025, respectively). There was no statistically significant difference between the post-exercise values in the standing position.
The combined effect of posture and exercise was expressed as the change in blood flow determined by subtracting the baseline value from the post-exercise blood flow while sitting on the saddle. The combined effects on the wide and narrow saddles were 0.34±0.49 and -0.38±0.49, respectively (P<0.001). The negative value on the narrow saddle reflects post-exercise blood flow on the narrow saddle that is less than the baseline value.
Discussion
Penile blood flow increases with exercise as long as there is no external force applied to impede blood flow, as suggested by the measurements in the standing position. After 5 min of bicycling, an increase in blood flow to approximately 130% baseline was observed in the standing position, irrespective of saddle type. On the other hand, penile blood flow decreases upon sitting on the saddle. These reductions in penile blood flow occur in the face of physiologic increases in penile blood flow after cycling, and, in the case of the narrow saddle, the act of sitting reduced penile blood flow to 76% of baseline while the same conditions on the wide saddle reduced blood flow to 119% of baseline.
The observed increase in blood flow could probably be explained as a combination of a bystander effect and a direct effect of exercise. Sullivan et al6 demonstrated a near-linear relationship between blood flow to the lower extremity and oxygen consumption. Increased perfusion of the perineal area is most likely secondary to increased blood flow to the lower limbs. Additionally, although the penis is hardly considered the 'exercising limb' during bicycling, anatomic considerations and the results of this study suggest that the perineum undergoes variable yet continuous compression potentially causing a condition of increased oxygen demand, albeit due to decreased perfusion rather than increased metabolic activity. In fact, Sommer et al7 reported no increase in penile blood flow when cycling in the standing position. Whether the increase in blood flow is simply a reflection of increased blood flow to the entire lower extremities or a reflection of a compensatory physiologic response to increased oxygen demand cannot be concluded from the data.
Explanation of the reduction in penile blood flow caused by sitting on the saddle should begin with anatomical considerations of relevant structures in the lower abdomen and perineum. The common penile artery lies medial to the inferior pubic ramus and bifurcates into the cavernosal and dorsal arteries just below the symphysis pubis. They are continuations of the internal pudendal artery in the male, which originates from the anterior trunk of the internal iliac artery. The pudendal nerve passes through Alcock's canal and comes out below the symphysis pubis to provide sensory innervation of the perineum and genitals. Given these anatomic positions, the penile arteries and pudendal nerves may be compressed between the bike saddle and the pubic bones during bicycling.8
It is perhaps noteworthy that laser Doppler flowmetry was targeted at the dorsal artery of the penis rather than the cavernosal artery, which provides the principal blood supply to the glans penis. In defense of the selected approach, blood flow in the cavernosal artery is difficult to detect in the flaccid penis, and, since both the dorsal and cavernosal arteries branch from the penile artery, it is believed that reduction of blood flow in the dorsal artery is indicative of reduction of blood flow in the cavernosal artery. While previous noninvasive methods have focused on the transcutaneous measurement of penile oxygen pressure,7 our study offers a method of determining accurate blood flow measurements through laser Doppler flowmetry.
There may be an additional role of the bony pelvis in the reduction of penile blood flow aside from simple compression at the pubic arch. The transverse diameter of the inferior pelvic aperture (bituberous diameter) is the distance between the medial sides of the lower limits of the ischial tuberosities. The mean bituberous diameters in adult males and females are 85 mm and 118 mm respectively.9 Any portion of the saddle anterior to the ischial tuberosities that may be narrower than the bituberous diameter would effect wedge compression to the perineum.
It is common knowledge that the ischial tuberosities are normally the principle points of load bearing in the seated position. When sitting in a chair, the weight of the body is primarily distributed over the corresponding surface area of the gluteal region and part of the proximal posterior thigh (hamstring). On a bicycle saddle, the two ischial tuberosities effectively form a fulcrum about which the body weight can be pivoted, making anterior, neutral and posterior sitting postures possible. The anterior portion of the bike saddle literally applies wedge compression to the inferior aspect of the urogenital region of the perineum and to part of the anal region. Severity and area of perineal compression would vary with body weight and the degree of forward leaning. Kerstein et al10 reported that weight correlated with reduced penile pressure due to perineal compression in cycling.
Blunt trauma to the perineal region of the corpora cavernosa has been considered a risk factor for the subsequent development of erectile dysfunction.1,3,4 Munarriz et al1 noted that sports-related accidents were the most common type of blunt injury to the perineum leading to erectile dysfunction. Anderson et al2 performed a survey-based study of amateur and professional cyclists after a single bicycle race, where 21% of males experienced genital numbness, and 13% of males reported impotence.
Susceptibility to injury from blunt trauma can derive from the structure being fixed and related to a firm undersurface.1 Structures of particular concern for traumatic wedge compression by a bicycle saddle are those found in or passing through a roughly triangular space that is bordered bilaterally by the pubic arch, with the symphysis pubis at the apex, and the ischial tuberosities forming the base. These are essentially the same structures entertained by the anatomic considerations.
Both vasculogenic and neurogenic mechanisms seem plausible as explanations of the development of bicycling-associated perineal symptoms and erectile dysfunction. Anderson et al proposed nerve entrapment as an adverse effect of long-distance cycling.2 Our study demonstrated significant reductions in penile blood flow immediately after a brief exercise period. It was not the intention of the study to investigate neurogenic mechanisms per se, and it is believed that the experimental design essentially eliminates the possibility of developing nerve block in the time allotted for the study. However, it would be of interest to investigate the temporal relationship between the two mechanisms.
A significant unresolved issue is the transition from acute to chronic reductions in penile blood flow. While it is assumed that normal subjects would quickly recover after a 5 min bicycle ride, there may be a point at which a normal subject does not recover. Unfortunately, our study design did not include monitoring the volunteers until flow returned to baseline values.
It would be of particular benefit if an animal model of load (body weight)-induced perineal trauma could be developed for further investigation into the pathophysiology of penile artery insufficiency. Chevalier et al11 published a case report of endofibrosis of the external iliac artery in a small number of professional bicycle racers. The suggested pathophysiology involved a combination of anatomic and biomechanical considerations, arterial stress of the high flow state, increased blood pressure and subsequent turbulent flow. This seems to represent a type of vascular pathology that is unique to professional bicycle racers; however, it is quite possible that blunt perineal trauma could present a more common form of vascular pathology that is not limited to professionals.
Conclusions
The shape of the bicycle saddle clearly affects penile blood flow. This is of particular concern during exercise and in the post-exercise state, where the narrow saddle demonstrates more significant reductions in penile blood flow than the wide saddle. In light of the results of this study and mounting anecdotal evidence of erectile dysfunction in avid cyclists, it appears that reduction in penile blood flow caused by saddle shape could serve as an initial step in the development of vasculogenic impotence in some individuals. While behavior modifications (eg increasing the number of rests, standing on the pedals to relieve perineal pressure, etc.) might help to diminish this effect, industry-wide modifications in saddle design might be required to completely eliminate a potentially detrimental side effect in the health-promoting sport of cycling.
S-J Jeong 1, K Park 2, J-D Moon 3 and S B Ryu 2
1 Research Institute of Clinical Sciences, Chonnam National University Medical School, Gwangju, Republic of Korea
2 Department of Urology, Chonnam National University Medical School, Gwangju, Republic of Korea
3 Department of Occupational and Environmental Medicine, Chonnam National University Medical School, Gwangju, Republic of Korea
Correspondence to: K Park, Department of Urology, Chonnam National University Medical School, 8-Hak-dong, Dong-Ku, Gwangju 501-757, Republic of Korea.
http://www.nature.com/ijir/journal/v14/n6/full/3900929a.html
