But they found one exception: Men who biked for at least five hours per week had fewer and less active sperm than couch potatoes.
Looking specifically at exercise, they found that men who exercised regularly -- even vigorously -- were no more likely to have problems with the quality or quantity of their sperm than men who never exercised.
However, they saw that men who said they spent at least five hours per week biking were twice as likely to have both a low sperm count, and relatively few sperm with healthy movement.
It's possible that trauma or temperature increases in the scrotum may explain the relationship between biking and semen health, "but more research is needed to investigate these mechanisms further."
It's also too early to say that regular biking caused the sperm problems, Wise cautioned. "More studies are needed to replicate our findings before they can be considered causal."
