Many contributors have been linked to male-factor infertility. One factor that's often overlooked is bicycling. One problem with cycling is the rising temperature of the testicles from exercise and sitting for a long period of time. Testicular temperatures over 93 degrees can hinder production or even destroy what's already stored there. Another part of cycling is problematic. The vibration and jolting are concentrated between the legs and in the crotch area. Riding on a narrow seat for extended periods can exert a lot of pressure on the testicles and other parts of the male reproductive anatomy like the prostate and the tubes connecting the testes to the urethra. There's no scientific link between bike riding and low sperm counts. If there's no problem with your sperm count or motility, you don't have to worry about the effects of cycling. However, if you have a male-factor fertility problem, you might try putting the bike away for a while.
