Research from the 2010 Annual European Society of Human Reproduction and Embryology (ESHRE).
The researchers studied triathletes and found a significant correlation with cycling time and intensity and poor sperm analyses – particularly sperm morphology.
They believe more research is necessary however, they hypothesize that perhaps the heat or pressure on the testicles caused the depressed morphology.
Morphology reflects sperm function better than sperm counts or motility. These data suggest that high intensity cycling can impair sperm parameters and likely fertility.
Professor Vaamonde’s team has previously shown that both high exercise intensity and high exercise volume may be detrimental to sperm quality. They looked at the triathletes to assess the correlation between the volume of training in each activity and sperm quality. Of the three modalities, only cycling, which required the most training, showed a clear correlation with sperm quality. The more cycling training the sportsmen undertook, both in time and kilometres, the worse their sperm quality became.
“While all triathletes had less than 10% of normal-looking sperm, the men with less than 4% – at which percentage they would generally be considered to have significant fertility problems – were systematically covering over 300km per week on their bicycles.”