Rubuta ci gaba don wannan sakin layi - An haifi Prieto a Segovia, kuma ya fara fitowa a gasar zakarun Turai ta 1983 a gasar zakarun Turai, inda ya zama na biyar a cikin mita 10,000. Ya zo na bakwai a tseren tseren kilomita 20 a gasar cin kofin duniya ta 1985 IAAF sannan ya ci gaba da lashe lambar tagulla a gasar a gasar zakarun Turai ta 1986. Ya kafa kansa a matsayin daya daga cikin manyan masu tafiya a Spain, yana fafatawa a Gasar Cin Kofin Duniya a Wasanni a 1987 da 1991. Prieto ya lashe lambar yabo ta biyu ta kasa da kasa a gasar Universiade ta 1989, inda ya kasance mai lambar azurfa a cikin tafiyar kilomita 20 a bayan Walter Arena na Italiya. Ya zo na 13 a gasar zakarun Turai ta 1990
kuma ya gama da wuri daya kasa da cewa a 1991 IAAF World Race Walking Cup.