Groin Numbness and Bike Riding (cont.)
Perineal symptoms are not experienced by all cyclists, but this is certainly something to be aware of, particularly if you plan to ride long distances.
What are factors that cause perineal symptoms?
Vertical loads of the perineum to the saddle can be as high as 52% of the rider's body weight, whereas shear loads can reach 12% of body weight. The vertical pressure is dependent on the rider's body weight as well as riding position. Although there is no conclusive data as to what degree of load increases the likelihood of symptoms, there does appear to be a relationship between load stress and compression of the perineum.
Saddle and handlebar height
In a study of erectile dysfunction and bicycle characteristics, researchers determined that keeping handlebar height lower than saddle height in long-distance cyclists was associated with less erectile dysfunction, perhaps because this configuration puts the rider in a leaning-forward position which may reduce vertical load on the perineum. This position may or may not apply to recreational riders on touring or hybrid bikes where speed and aerodynamics are not as important, but there is no research to support the claim one way or the other.
In three studies of the angle of the saddle, it was confirmed that a downward tilted saddle reduced stress and compression on the perineum. This is probably because the backward stress puts the weight of the rider on the ischial tuberosities (the "sit bones" in your buttocks) and off of the perineal cavity.
Bicycle saddle design has been the target of a great deal of scholarly and commercial research. A number of years ago, bicycle saddles started to be manufactured with cutouts down the middle with the hope that this would relieve pressure on the perineum and reduce compression symptoms. Indeed, in one study, 55% of the subjects ranked the partial cutout saddle as the most comfortable. In a recent study of a new saddle (Selle SMP) with a large cutout and downward facing nose (the front of the saddle), the saddle was clearly superior in preventing vascular compression and penile blood flow occlusion compared with more standard saddle designs.
Interestingly, in a study on saddle shape and penile blood flow, a narrow saddle was associated with greater reductions in penile blood flow than a wider saddle, leading the researchers to conclude that the narrow saddle could be a source of blunt perineal trauma. In a study involving computer analysis of forces on the perineum with wide and narrow saddle design, it was also shown that a wide saddle capable of supporting the sit bones was superior for reducing perineal stress compared with a narrow saddle. Most racing saddles, however, are narrow, and this may have some effect on perineal symptoms for some riders. In a study of a saddle without a nose compared to a traditional saddle with a protruding nose, the traditional saddle was associated with two times greater perineal pressure than the noseless saddle. These results have been confirmed by another study. However, it has been reported by riders that noseless saddles lead to a feeling of less control over the bike since their thighs are not fully in contact with the saddle. More research needs to be done on optimal width and shape of the saddle.