Wariner driven by rivalry with Merritt

Jeremy Wariner's budding rivalry with fellow American LaShawn Merritt has fueled the Olympic and world 400m champion with a new desire to excel.

"For me it's great to have a rivalry," the 24-year-old Wariner told a news conference. "It makes me train harder. When I go to the track I know LaShawn will be there working as hard as I am."

Wariner had not lost a 400m race for more than a year when Merritt beat him in Berlin in June. Merritt also defeated Wariner at the US Olympic trials before the latter bounced back to claim victories in Rome and Paris.