The answer, they say, cannot lie solely in the latest high-tech swimsuits introduced amid a swirl of controversy this winter, because the world-record smashing began at last year’s world championships — long before the newest of the newfangled apparel came out.

Swimmers, coaches and scientists say it is impossible to pinpoint one explanation. They cite many contributing factors, ranging from professional training groups that have sprouted across the United States to greater access to underwater cameras and other advanced technology.

But some say the most significant breakthrough has been a revival of a swimming maneuver developed more than 70 years ago by one of the physicists who worked on the atomic bomb.

Though utilized for decades, the underwater dolphin kick had not been fully exploited by the swimming mainstream until Olympic megastar Michael Phelps and a few other stars began polishing it — and crushing other swimmers with it — in recent years.

The underwater dolphin kick attracted the interest of swimming innovators as early as the 1930s. The late Volney C. Wilson explored its possibilities before diving into later work on nuclear fission and the atomic bomb, according to David Schrader, a research professor at Marquette University who is Wilson’s biographer.

Schrader said Wilson, an alternate on the 1932 Olympic water polo team who studied fish propulsion at a Chicago aquarium, claimed to have shown the kick to Johnny Weissmuller, a training mate at the Illinois Athletic Club. “Weissmuller reproduced it perfectly, but was not impressed by it,” said Schrader in a phone interview, recalling a conversation with Wilson.
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One of the first swimmers to turn heads with the underwater dolphin kick was David Berkoff, a Harvard graduate who became known for the “Berkoff Blastoff.” In 1988, Berkoff set several world records in the 100 backstroke by dolphin-kicking for 35 meters underwater at the start of the race.