Bicycle saddle shape affects…..

December 2002, Volume 14, Number 6, Pages 513-517

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. 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.

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 a 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.

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.

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.

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. 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.

Susceptibility to injury from blunt trauma can derive from the structure being fixed and related to a firm undersurface. 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.

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.

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.
Nature – journal/v14/n6/full/3900929a
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.

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