Bicycle seat neuropathy is one of the more common injuries reported by cyclists. [1, 2, 3, 4, 5] The injuries and symptoms are due to the cyclist supporting his or her body weight on a narrow seat, and they are believed to be related to either vascular or neurologic injury to the pudendal nerve. [2, 5, 6, 7, 8, 9, 10]
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A wide frequency range has been reported for bicycle seat neuropathy, but it is believed to be underreported. The medical literature contains several case reports of reversible neuropathy [5, 9] and several retrospective studies surveying participants in long-distance cycling races and tours. [8, 11, 12]
Andersen and Bovim surveyed 260 cyclists participating in a long-distance bike tour that was 335.54 miles (540 km) in length.  Of responding males, 35 (22%) reported symptoms of either numbness or pain in the pudendal area. Thirty-three (21%) males reported penile numbness, with 10 (6%) male cyclists reporting symptoms that lasted longer than 1 week. In addition, 21 males (13%) reported symptoms of impotence, 11 of whom experienced symptoms for longer than 1 week, and 3 of whom reported impotence lasting longer than 1 month. 
Kuland and Brubaker reported that during the 1976 Bikecentennial tour, there was a 7% incidence of pudendal and/or penile numbness, but this study only surveyed 89 of 1200 participating cyclists. 
Weiss studied symptoms of cyclists participating in a 500-mile (804.97 km) bicycle tour.  Of the participating cyclists, 45% reported at least mild and transient perineal numbness; 10% reported the symptoms as severe, and 2% of the cyclists had to temporarily stop riding. Perineal numbness has also been documented in women cyclists. LaSalle et al surveyed 282 female members of a Dallas cycling club.  In this group, 34% of the women reported perineal numbness.
Potter et al assessed the differences between men and women with regard to bicycle saddle pressure distribution during seated cycling.  The authors noted that there were significant differences between the sexes in saddle loading, and these differences were especially relevant with regard to the position of the bicycle handlebar positions. In particular, the drops hand position shifted the rider's weight, such that more weight was supported on the anterior pelvic structures. 
The cause of bicycle seat neuropathy has been attributed to several different ischemic events. Amarenco et al and Oberpenning et al hypothesized that compression of the pudendal nerve as it passes through the Alcock canal causes the condition. [9, 15] The Alcock canal is enclosed laterally by the ischial bone and medially by the fascial layer of the obturator internus muscle. The pudendal nerve exits the canal ventrally, below the symphysis pubis, and innervates the genital and perineal regions.
Oberpenning et al postulated that long-distance cycling results in the indirect transmission of pressure onto the perineal nerve within the Alcock canal.  Weiss and Bond separately proposed that bicycle seat neuropathy is due to temporary and transient ischemic injury to the dorsal branch of the pudendal nerve secondary to compression of the nerve between the bicycle seat and the symphysis pubis. [12, 16] Weiss also theorized that the genital branch of the genital-femoral nerve could be involved in cases in which scrotal paresthesia is reported. 
Bicycle seat design (eg, shape) may be the major extrinsic factor for the development of bicycle seat neuropathy. [1, 4, 6, 17, 18, 19, 20, 21] Results of computer modeling reported by Spears et al showed that wider bicycle seats that support the ischial tuberosities decrease pressure on the perineal area.  Other studies have also demonstrated the effect bicycle seat design has on penile blood flow  and penile oxygen pressure.