Four major traits are evaluated when a semen analysis is performed: seminal volume, sperm concentration, sperm motility and sperm morphology. The interaction of those four traits is an indication of normal testicular function and, thus, the male's ability to provide sufficient numbers of normal, motile sperm to effect pregnancy. The product of seminal volume and sperm concentration yield the number of sperm available. Sperm motility is the percentage of those sperm that are actively swimming. Sperm morphology is the percentage of sperm that have normally shaped heads and tails. Although sperm numbers and sperm motility receive much attention when men (and their wives) swap semen quality results, sperm morphology, while an important quality trait, is often ignored. Abnormal sperm morphology may take the form of broken or misshapen tails, which would impair the sperm's swimming ability. An abnormally shaped sperm head may indicate that DNA structure or DNA packaging is not what it should be. This could possibly impact swimming ability, fertilizing ability or the ability of the male genome to make its appropriate contribution to supporting normal embryonic development.
A small Spanish study of 15 triathletes showed that men who cycle more than 186 miles per week had less than 4% morphologically normal sperm. When evaluated using strict criteria, a 'normal ' level of morphologically normal human sperm is between 10% and 15%. Thus the levels of abnormally shaped sperm found the cyclists could lead to fertility problems. It is thought that tight clothing and the friction against the saddle of the bicycle seat could contribute to the sperm abnormalities as other training routines such as running or swimming did not show the same abnormalities. The effects of the extreme cycling would likely disappear upon stopping or reducing the level of cycling. Nonetheless, it may be prudent for professional cyclists to freeze sperm prior to training or accept that their fertility may be affected during and for up to 3 months after extreme training. It is important to note that if this data is correct it only applies to extreme cycling....not your average cycler.