From the Department of Epidemiology, School of Public Health and Community Medicine, University of Washington and the Department of Urology, Virginia Mason Medical Center, Seattle, Washington
Purpose: We conducted a prospective cohort study to examine the relationship between bicycle characteristics and the occurrence of erectile dysfunction.
Materials and Methods: Subjects consisted of 463 cyclists completing a cycling event of at least320 km who were free of erectile dysfunction before their event.
Results: The cumulative incidence of erectile dysfunction after the ride was 4.2% (95% confidence interval [CI] 2.4%-6.8%) and 1.8% (95% CI 0.7%-3.8%) 1 week and 1 month after the event, respectively. Bicycle characteristics associated with an increased risk of erectile dysfunction included a mountain bicycle compared with a road bicycle (risk ratio ERR] 4.1, 95% CI 1.6-12.5), and the relative height of the handlebars parallel with or higher than the saddle compared with the relative handlebar height lower than the saddle (RR 3.0, 95% CI 1.1-9.3).
Perineal numbness during the ride was experienced by 31% of the cyclists and was associated with erectile dysfunction (RR 4.4, 95% CI 1.6-12.7). Saddle cutouts were associated with an increased risk of erectile dysfunction among those who experienced numbness (RR 6.0, 95% CI 1.3-27.1), but the association was reversed among those who did not report numbness (RR 0.3, 95% CI 0.0-2.5).
Conclusions: If the associations described are causal, then cyclists on a long-distance ride may be able to decrease the risk of erectile dysfunction by riding a road bicycle instead of a mountain bicycle, keeping handlebar height lower than saddle height and using a saddle without a cutout if perineal numbness is experienced.
KEY WORDS: bicycling, impotence, exercise, hypesthesia
Some authors have suggested that bicycle characteristics may induce erectile dysfunction (ED) among some riders.1-5 Compression of the neurovascular bundle from sitting on the saddle is considered a possible mechanism. As a result new bicycle saddles have been constructed with “cutouts” or significant grooves that are intended to relieve pressure around the pudendal nerve and artery, and thereby decrease associated erectile dysfunction. In addition, wider, more padded saddles are now marketed, partially based on a study reporting that this type of saddle results in less restriction in penile blood flow compared with a narrow, unpadded saddle.1 Other suggested risk factors for cycling related erectile dysfunction include bicycle fit, (3,4,6) riding technique (3,7) and body weight.(7) To date no controlled epidemiological study has estimated the association among these characteristics and cycling related erectile dysfunction. Therefore, we conducted a cohort study to test the null hypothesis that there is no relationship between bicycle characteristics and the occurrence of erectile dysfunction after a long-distance cycling event.
Between June 1999 and July 2001 we conducted a prospective cohort study of cyclists who participated in 1 of 6 different recreational bicycle rides of at least 320 km (table 1). Subjects could participate if they were sexually active, age 21 years or older, reported normal erectile function, were registered in 1 of the events listed in table 1 and had Internet access. Cyclists who did not complete the intended ride were excluded from study, leaving 463 available for study (see figure). Study procedures were approved by the Human Subjects Review Committee of the University of Washington.
Data collection.
Eligible ride registrants completed informed consent and 3 separate questionnaires over the Internet. Access to the questionnaires was password protected, and no personal identification was recorded on the questionnaire. However, the 3 questionnaires on a given cyclist could be linked using his self-selected password. We collected data at 3 times, including 1 week before the event, and 1 week and 1 month after the event.
On the 1 -week post -ride questionnaire cyclists reported the type of bicycle used during the ride (road, mountain/hybrid or recumbent). The 11 men who rode recumbent bicycles were not included in the analysis. To obtain other information on bicycle characteristics we used pictures and written descriptions to assist the participants. To describe the relative saddle width we used top views of 3 different width saddles. The relative thickness of the saddle padding was pictured using a side view, with options of none, moderate or thick. We asked participants whether their saddle had a cutout, or other deep grooves or wedges designed to relieve pressure. The so-called “body geometry” style of saddle containing a deep split in the back and a groove down the middle was classified as a saddle with a cutout.
We asked the participants to assess the relative tilt of the saddle using 3 side views of a saddle with the nose pointed upward, parallel to the ground or pointed downward. Similarly, we used side views to determine the relationship of saddle height to the top of the handlebars. Either the handlebars were higher than the saddle (signifying a more up-right cycling posture), even with the saddle or lower than the saddle (signifying a more forward leaning posture).
Erectile Dysfunction: Erectile function was determined using erectile function domain questions 1 through 5 and question 15 from the International Index of Erectile Function. This self-administered questionnaire has been reported to be reliable and valid for assessing erectile dysfunction, it has a test -retest repeatability correlation coefficient of 0.84, 0 and a sensitivity and specificity of 0.98 and 0.85, respectively.(9) Each question has an ordered scale with 5 as the maximum score. The responses to the 6 erectile function questions were summed and a subject with a score of 25 or lower was considered to have erectile dysfunction.(9)
Potential Confounding Variables: Potential confounding variables included age, body height and weight, prior and current tobacco use, current alcohol consumption, frequency of training 3 months before the ride and number of prior endurance rides completed. History of hypertension and diabetes were recorded, as well as current medication use. As a measure of cycling experience we asked the participants the number of “century” rides (161 km or longer) they previously completed and the number of years they cycled regularly. Training distance 3 months before the ride was measured as the number of kilometers per week cycled. We asked participants the number of hours of riding it took to complete the event (not counting time at rest stops) and calculated average speed. Cyclists also reported whether or not they experienced perineal numbness on the current ride (current perineal numbness) and during the 3 months before the ride (pre -ride perineal numbness).
Reliability of Bicycle Characteristics: An investigator (JRD) inspected the bicycles of a subset of 27 subjects at a rest stop during 1 of the cycling events to compare the agreement between cyclists and an investigator with respect to bicycle characteristics. Cohen’s k10 for reporting bicycle characteristics was 1.00 for saddle cutout, 0.75 for bicycle type, 0.65 for saddle width, 0.61 for handlebar height, 0.57 for saddle padding and ā€”0.06 for saddle tilt.
Data analysis. Data regarding the erectile function score were missing in 17% of the cyclists for the 1 -week post-ride questionnaire. Therefore, we formed 4 age categories (21 to 30 years. 31 to 40,41 to 50 and 51 years or older), and within each age stratum of age we imputed missing values for erectile function scores using an approximate Bayesian bootstrap method.” This imputation process using bicycle characteristics and erectile dysfunction variables was performed 10 times. All multivariate analyses that used imputed information were performed on each of the 10 imputed data sets, and all estimates, variances and confidence intervals (CIs) were calculated using methods suitable for combining data from multiple imputations.(12,13)
All bicycle characteristics and potential confounders were assessed with univariate and multivariate analyses for association with erectile dysfunction 1 week after the ride. We used negative binomial regression to calculate the adjusted risk ratios (RRs).” Continuous variables were entered as linear terms and other transformations of these variables did not appreciably change the estimate of association.(15) Bicycle characteristics that were ordered and contained fewer than 25 subjects in a category were collapsed to the adjacent category. Each bicycle characteristic was modeled separately using a backward selection process. We initially considered variables for model inclusion with pā‰¤0.2. Age and the 1 covariate that influenced the risk ratio the most in the selection process for a given bicycle characteristic were included in the final adjusted model.
Because perineal numbness was considered a precursor to cycling related erectile dysfunction, we assessed the association between current perineal numbness and erectile dysfunction, and between current perineal numbness and bicycle characteristics. Perineal numbness occurs in some cyclists but not in others. We speculated that numbness while riding may serve as a marker for men whose perineal anatomy makes them unusually vulnerable to the mechanical compression effects of certain bicycle characteristics. Therefore, we also explored the possibility of effect modification between current perinea’ numbness and 1 or more bicycle characteristics using stratified analysis. STATA (Version 6.0, College Station, Texas) was the statistical package used for the analysis.(16)
The baseline questionnaire was completed by 463 cyclists. The 1 -week questionnaire was completed by 383 cyclists (84%) and all but 26 attempted sexual intercourse during the last week. The 1 -month questionnaire was completed by 343 cyclists (74%) and all but 4 attempted intercourse during the month after the ride (see figure). Compared with cyclists who completed the 1 -week post -ride questionnaire, cyclists who did not complete the 1 -week post -ride questionnaire tended to weigh slightly less (82.8 kg [SD 11.4) vs 84.9 kg [SD 11.9], smoke less (2.9% vs 5%) and drink alcohol slightly more (80.9% vs 74.2%). Otherwise these 2 groups of cyclists were similar (table 2).
The cumulative incidence of erectile dysfunction was 4.2% and 1.8%, 1 week and 1 month after the ride, respectively. Cycling related erectile dysfunction during the week after the ride was not significantly associated with age, height, weight, concurrent medical conditions, tobacco use, training mileage, past experience or speed during the event (table 3). There was a modest association between the number of prior century rides (161 km or longer) and erectile dysfunction, with those with no or little experience cycling this distance having the highest risk (table 3).
Riding a mountain bicycle compared with a road bicycle was associated with an increased risk of erectile dysfunction. The risk ratio adjusted for age was 4.1 (95% CI 1.6-12.5). The relative height of the handlebars parallel with or higher than the saddle compared with relative handlebar height lower than the saddle was also associated with a higher risk of erectile dysfunction; and the risk ratio adjusted for age and bicycle type was 3.0 (95% CI 1.1-9.3, table 4). Little association was found among erectile dysfunction and saddle with a cutout were at slightly greater risk for erectile dysfunction compared with those without a saddle cutout after controlling for age and bicycle type, although this risk ratio estimate had wide confidence limits (RR 2.0, 95% CI 0.6-6.2).
Perineal numbness was experienced by 31% of the cyclists on the current ride and was associated with erectile dysfunction (RR 4.4, 95% CI 1.6-12.7). There was little association between current perineal numbness and any bicycle characteristics (table 4). Saddle cutouts modified the association between perineal numbness and erectile dysfunction, with increased risk among those who experienced numbness (RR 6.0, 95% CI 1.3-27.1) and decreased risk among those who did not report numbness (RR 0.3, 95% CI 0.0-2.5, table 5). The interaction between saddle cutouts and current numbness in relation to erectile dysfunction risk was statistically significant at p = 0.001. Perineal numbness data from before the ride were available for the 206 cyclists in the 2000 and 2001 cycling events. Saddles with cutouts were used by 51% of cyclists who did not experience pre -ride numbness and 63% of the cyclists who did report pre -ride perinea’ numbness. Pre -ride numbness did not confound the relationship between cutouts and erectile dysfunction.
We found an increased risk of erectile dysfunction among men who cycled on a mountain bicycle compared with a road bicycle (RR 4.5), or cycled with the handlebar height even with or higher than the saddle compared with a handlebar height lower than the saddle (RR 3.1) 1 week after an endurance bicycle ride. There was little association among erectile dysfunction and saddle width, saddle padding or saddle tilt. Cyclists who rode with a saddle cutout had an increased risk of erectile dysfunction compared with those whose saddle had no cutout, particularly if current perineal numbness was experienced.
Study limitations. With only 15 cyclists reporting erectile dysfunction our study had limited power to detect differences between exposure categories. Our method of acquiring information about bicycle characteristics using verbal and pictorial clues over the Internet was effective for some characteristics but proved to be less reliable in assessing others. When measurements are difficult to replicate, nondifferential misclassification may arise which will tend to bias the risk ratio in the direction of no effect.(17) This may explain why little association was found between the saddle tilt variable and erectile dysfunction.
Selection bias is another potential study limitation, although we excluded from study all cyclists who reported erectile dysfunction before the event. If cyclists who had a tendency toward erectile dysfunction in the past were more willing to participate compared with those who had no prior problem, the risk of erectile dysfunction would be exaggerated. On the other hand cyclists prone to erectile dysfunction associated with their athletic event may have stopped cycling altogether. The result would be a higher proportion of cyclists less prone to the problem volunteering for the study, thereby causing us to underestimate the true risk. Response bias is also possible since nearly 20% and 26% of cyclists did not respond to the first or second followup questionnaire, respectively. Finally, we looked at erectile dysfunction with an acute onset after a single cycling event and that resolved in most cases within a month. This outcome may not be related to chronic erectile dysfunction.
Bicycle type and handlebar height. The increased risk of erectile dysfunction associated with riding a mountain bicycle compared with a road bicycle may be due in part to the more upright posture that often results from riding a mountain bicycle. This idea is supported by our handlebar height data in that cycling with handlebars higher than the saddle posed a greater risk of erectile dysfunction compared with cycling with handlebars that are lower, after adjusting for age and bicycle type. A cyclist’s body weight is supported through the hands, buttocks and feet. An upright posture causes more body weight to be borne through the buttocks. Other factors may also explain our findings. For instance, the casual cyclist who has less experience riding long distances may be more likely to ride a mountain bicycle on a long-distance cycling event. In our study 56% of those who used a mountain bicycle had 2 or less years of experience compared with 34% of those who used a road bicycle. Experienced cyclists may shift the weight off their buttocks more frequently by standing on the pedals or may tend to push on the pedals with more force, transferring weight from the buttocks.
Erectile dysfunction and perineal numbness. The mechanism explaining the observed relationship between cycling related perineal numbness and erectile dysfunction is not clear. We noted a strong association between current perinea] numbness and erectile dysfunction (RR 4.4). In previous studies a relatively large proportion of cyclists experienced perineal numbness with cycling, the prevalence ranging from 10% to 70%.(2,6,7,18-20) However, cycling related erectile dysfunction is reported less frequently.(2,7,18) In our study 31% of the cyclists reported numbness during or after the ride but only 4% experienced erectile dysfunction. Of these cyclists 5 (33%) did not experience current perineal numbness.
We found no association between any bicycle characteristics and current perineal numbness. However, we did find a strong association between numbness and erectile dysfunction, particularly when cyclists used a saddle with a cutout. Erectile dysfunction was more likely to develop in those who experienced numbness and cycled with a cutout saddle than in those who experienced numbness and did not cycle with a cutout saddle. Perineal numbness may be a surrogate for an exposure that we did not measure. Numbness may identify a perineal anatomy that makes nerve and vascular structures unusually vulnerable to the external pressure of sitting on a bicycle saddle. Cutout saddles to include the body geometry style that are designed to prevent numbness and erectile dysfunction may not fit cyclists who have this vulnerable anatomical variation. Instead of relieving pressure over the pudendal canal, the edges of the cutouts or the overall decreased surface area of the saddle may create greater force against these important structures. As a result the combination of a saddle with cutouts plus the vulnerable anatomical variant for which numbness may serve as a marker increases cyclist risk of erectile dysfunction.
If the associations that we have described are causal, then men who go on a long-distance bicycle ride may be able to decrease the risk of erectile dysfunction if they ride a road bicycle instead of a mountain bicycle, keep the handlebar height lower than the saddle and switch to a saddle without a cutout if they experience perineal numbness while using a saddle with a cutout. Larger studies should be done to confirm these associations and to isolate the contributions of each specific feature to erectile dysfunction risk.
Alan Burgstahler (Seattle to Portland), Diane Loupe (Bicycle Ride Across Georgia) and Jim Green (Register’s Annual Great Bicycle Ride Across Iowa) organized each cycling event involved in this study.
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