"There have been a couple studies going both directions," Dr. Oz says. According to Dr. Oz, the testicles are located outside a man's body in order to keep them cooler so the sperm can mature at the proper rate. "If you're putting on tight pants, especially if you're getting hot for other reasons, you actually can make it a little uncomfortable for the sperm and you may influence fertility rates."
Hot tubs can present another temperature issue for men. "Most of the time, I tell folks to spend less than a half an hour in a really hot environment and you'll be okay," Dr. Oz says. "But if you go past that period of time, and some folks do, you probably can affect fertility."
Some men are concerned that riding a bicycle can affect their fertility, but Dr. Oz says impotence, not fertility, could be the issue. A bicycle seat can restrict blood flow to the penis, Dr. Oz says, so it's important to make sure the seat actually fits to your body.
"This is important for women, too, because if women don't get blood supplying to their equivalent of the penis, which is the clitoris, it doesn't get hard," he says. "And so during orgasms or during sex, it won't get hard because blood's not going to it normally, so it can actually influence the quality of sex."