Men who log up 4800km or more a year on their mountain bikes suffer scrotal damage that could reduce their fertility.
A report, based on examinations of 40 "extreme" bikers and 35 non-cyclists, suggests that men who spend the most time on their bikes should invest in shock absorbers andsuspension systems.
Scrotal examinations of the bikers found that 88 per cent had cysts, calcification, varicose veins and other abnormalities compared with 26 per cent of the non-biking group.
Sperm samples showed that the extreme bikers had a count that was only a third that of the non-cyclists while bikers' sperm had less motility or movement than non-bikers.
"We believe that extreme mountain biking results in semen alteration, which may have an impact on fertility," said lead author Ferdinand Frauscher of University Hospital in Innsbruck, Austria.
