The biggest concern for some career cyclists and very dedicated hobbyists into cycling for long times is impotence.
There is a nerve and/or vascular issue centered in the area between the scrotum and the rectum…the nerves/vascular system in this area are bearing the load when the cyclist sits on the seat. Typically, the buttocks don’t rest on the seat so that leg motion is not inhibited.
Of course this is different than almost every other time we site, since the load goes on the very sensitive area where nerves and the vascualr system tie into the penis. If blood flow is restricted due to damage, or if nerves are damaged, it could very well lead to impotence.
From what I understand, it’s also a tricky kind of impotence to overcome, because the damage tends to have lasting effects.
Low sperm count and/or infertility is also a risk, but can be managed a bit better.
In both cases, prevention and awareness can help drastically.
But the impotence issue due to damage in that area is probably the biggest challenge for cyclists: Very delicate nerves and a delicate vascular system that effect erectile function, which take the brunt of a cyclists load when sitting.
New seats, sitting habits and other protective gear might help.