Three-times 200 metres winner Allyson Felix is among eight defending champions named in a powerful 129-member US world championships team announced by USA Track & Field (USATF) on Wednesday. The versatile Felix will attempt to become the first woman to win gold medals at both 200 and 400 metres in a World Championship during the August 27-September 4 competition in Daegu, South Korea. \"I think it is going to be extremely difficult but I am excited to challenge myself,\" Felix told Reuters in a recent interview. She also hopes to run on both the 4x100 and 4x400 metres relays, where she won gold in 2007. One of her chief rivals in the 400 will be defending world champion Sanya Richards-Ross, who last Saturday ran the year\'s second fastest time. Olympic and world men\'s 400 metres champion LaShawn Merritt, who recently completed a 21-month doping suspension, also returns. Five other 2009 world champions will be back for the Americans — 400 metres hurdler Kerron Clement, shot putter Christian Cantwell, decathlete Trey Hardee, and long jumpers Dwight Phillips and Brittney Reese. The team also has seven world leaders for 2011 in Reese, hurdler David Oliver, decathlete Ashton Eaton, high jumper Jesse Williams, women\'s sprinters Carmelita Jeter (100) and Shalonda Solomon (200) and pole vaulter Jenn Suhr. Talented sprinters Both Jeter and Walter Dix, the double Olympic bronze medallist, will tackle the 100-200 metres double against Jamaica\'s talented sprinters. The US 100 metres team and 4x100 metres relay pool also includes former Olympic and world champion Justin Gatlin, who finished runner-up to Dix in his second year back from a four-year doping suspension.