Cycling is excellent cardiovascular exercise and overall supports the blood-vessel health that erections depend on. However, sitting on a narrow saddle places pressure on the perineum, the area between the scrotum and anus, where key nerves and blood vessels to the penis run. Long hours can cause genital numbness or, in some men, contribute to erectile problems.
Vigorous cycling shortly before a PSA blood test can also temporarily raise PSA, which is why men are often advised to avoid heavy cycling for a couple of days before testing to prevent a falsely high reading.
Most effects are preventable. A well-fitted, wider or cut-out saddle, correct height, padded shorts, standing periodically, and avoiding excessively long unbroken rides reduce risk. See a doctor if you have persistent numbness or new erectile problems, and mention recent cycling if you are having a PSA test.