DOHA – Dalilah Muhammad of the United States set a new world record as she powered to victory in the 400 metres hurdles at the World Championships here Friday.Olympic champion Muhammad took gold with a time of 52.16 seconds at the Khalifa Stadium, bettering her own world record of 52.20 set at the US Trials in Iowa in July.Sydney McLaughlin of the United States took silver with a time of 52.23 while the bronze medal went to Rushell Clayton of Jamaica in a time of 53.74.