American Lochte is a three-time Olympic gold medallist
Ryan Lochte of the United States has set the first individual world swimming record since hi-tech bodysuits were banned at the start of 2010.
He won the 400m individual medley at the World Short Course Championships in Dubai in 3:55.50 - nearly two seconds faster than the previous mark.
Olympic 1500m champion Oussama Mellouli was second while Tyler Clary was third.
Russia's men set the 4x200m freestyle world record, shaving more than two seconds off the previous best time.
"I wasn't really expecting that," 26-year-old Lochte said of his second consecutive individual gold of the competition, having won the 200m freestyle on Wednesday. "I was going out there to race the field. I had no idea where I was at during the race."
Nikita Lobintsev, Danila Izotov, Evgeny Lagunov and Alexander Sukhorukov clocked a time of six minutes, 49.04 seconds as the Russians finished 0.54 seconds ahead of the quartet from America.
With China's women swimming to a new record in the 800m freestyle relay, only three new world marks have been set since the ban was introduced - all in Dubai.
In 2009, 29 world records were set in the first five days of the Fina [swimming's world governing body] World Championships in Rome.