"In the latest study, 15 triathletes with an average age of 33, were
asked not to have sex for three days before giving a sperm sample.
the results were compared with their training routines, only cycling -
not swimming or running - was linked with sperm quality.
the men - who had been training for an average of nine times a week for
eight years - had less than 10% of normal looking sperm, compared with
the 15-20% seen in the most fertile men.
In those who managed
more than 186 miles a week on their bikes, the proportion of sperm that
was the correct size and shape had fallen to 4%, the point at which men
may struggle to conceive without fertility treatment."
"Something which could be done would be to have their sperm frozen but
when they start training they do not realize what damage can be done to
their sperm," said Professor Diana Vaamonde, from University of Cordoba Medical School in Spain.