 Complete the following phrase:  A formidable competitor for most of her career, Richards-Ross ranked number one in the world from 2005-2009 and again in 2012 in the 400 meters. She holds the record for the most sub-50 second sprints in the history of the event, with a career total of 49 times. Richards-Ross also set the American 400-meter record of 48.70 seconds in 2006 and was named the IAAF 2006 Female World Athlete of the Year, an honor she received again in 2009. In addition to her individual achievements, Richards-Ross won three consecutive Olympic gold medals in the 4 × 400 meters relay at the 