Part of traditional martial arts training is conditioning the body to withstand hard blows by building up bone and muscular density. One kung fu tradition from China calls for the sensitive and vulnerable male genitals to be prepared to take heavy blows. Training involves ramming a steel-capped log into a student's groin.
This video from Luoyang, Henan province, China features masters of this conditioning practice, as well as "iron throat", "iron back", and "iron stomach." Those training regimens are also demanding, if somewhat less terrifying to men.
-via Geek Tyrant