Aaron Peirsol reclaimed the 100 metres backstroke world record on Wednesday, clocking 51.94 seconds at the US National championships.
Peirsol became the first man to dip under 52 seconds with the victory in the final at the championships, which also double as trials for the World Championships in Rome later this month.
Peirsol sliced .44 seconds off the mark of 52.38 set by Spain's Aschwin Wildeboer Faber during the lead-off backstroke leg in the 4x100 metres medley relay final at the Mediterranean Games on July 1.
The Olympic champion had trailed at the turn but surged on the second length, pulling away from the field to clinch the victory.
