] "Frequent mountain biking may reduce fertility in men,
] according to a small Austrian study that adds fodder to a
] debate over cycling and male sexual function.
]
] The research suggests frequent jolts and vibration caused
] by biking over rough terrain may cause abnormalities,
] including small scars within the scrotum and impaired
] sperm production.
]
] The abnormalities were found in professional mountain
] bikers and other "extreme" bikers who logged at least
] 3,000 miles yearly - or an average of more than two hours
] a day, six days a week. "

Better stay under that 3000 mile limit. :)