Nieves is a T12/B2 track and field athlete, who started running when he was 17 after his eyesight got bad. Because no one in his family ran, he started running at a park in Castrelos Vigo but not with the idea of doing it at the highest level. His first race was the 1998 Vigo half marathon. He was a member of the the Celta Vigo athletics club, then joined the Gymnastic Society of Pontevedra athletic club, before leaving the club to join the Alejandro Gomez Athletics Club.