I think fit and the seat make a difference. People who are riding/training like crazy may leave themselves open to problems, but there's no problem in this house. The only time my husband noticed any issue in that area of his body was about 4 years ago, when he rode 70 miles, including a big climb up a ski mountain road, with guys who were faster than him. The next day he went out to do a shorter ride and when he came back, he had blood in his urine. He got really freaked out, but I knew that was a sign of serious over training. It never happened again.

My son, who rode about 5-6,000 miles a year from age 14-18 and now runs like crazy has assured me there's "no problems in that area."