US researchers measured the blood flow in the tissues of the penis in 15 men who had suffered from problems getting an erection and who had a long history of bike riding.
An erection is caused by blood flowing into the penile tissues, which expand as a result.
Measurements of penile blood flow were taken from the men after they had been injected with prostaglandins to increase the flow of blood.
The men were either recumbent or sitting on one of three different types of bicycle seat:
The researchers found there were no significant differences in blood flow with either of the first two seat types.
However, the narrow, unpadded seat caused a significant reduction in blood flow in the arteries of the penis.
German researchers have also found evidence of a link between cycling and impotence.
They surveyed 1,114 amateur cyclists in local cycling clubs who pedalled 100 to 400 km per week, and compared the results to those from 155 active long-distance swimmers.
The rate of impotence in the cyclists was four per cent compared with two per cent for the swimmers.
The researchers also found that more than half the cyclists complained of numbness in the genitals.
The problem was more common among cyclists who travelled longer distances.
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