http://onlinelibrary.wiley.com/doi/full/10.1111/j.1464-410X.2008.07815.x

Studies on volunteers have shown that cycling while standing off the saddle does not alter penile blood supply after exercise, which remains the same as before exercise [ 4 ]. Numbness of the genital region is reported by >60% of the cyclists. There is a greater incidence of numbness and erectile problems in men who cycle regularly for longer training distances. As described earlier, penile blood flow is affected due to the compression of vessels by sitting on the saddle. In extreme cases endothelial injury can lead to vasculogenic ED [ 5 ]. This can be accentuated by the hard surface of the saddle. The neuropraxia of the pudendal nerve which supplies the posterior part of scrotum and base of penis can also lead to penile numbness and altered sensation during ejaculation [ 6 ]. It is important therefore to rest intermittently during prolonged and vigorous bicycle riding, thereby restricting the training distance.

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