If you are a regular cyclist, this may be important for you - a new study has found that cycling for at least five hours a week can affect a man's fertility.
Researchers at Boston University surveyed 2,200 men attending fertility clinics and found that men who cycle at least five hours a week have fewer and less active sperm than men who do not exercise at all.
The data were adjusted for body weight, blood pressure, choice of underwear and other variables, and found that men who exercised regularly were no more likely to have problems with the quality or quantity of their sperm than men who never exercised.
But when they looked at specific types of exercise, men who said they spent at least five hours a week cycling were twice as likely to have both a low sperm count and relatively poor sperm mobility.
This may be due to trauma or temperature rises in the scrotum, said study leader Lauren Wise.
"More studies are needed to replicate our findings before they can be considered causal," the Daily Mail quoted Wise as saying.
She also noted that it was possible that the men included in the study may not be representative of the general population, since they were all attending a fertility clinic and therefore more likely to have problems with their sperm.