Underwater phases off the start and each turn have crept closer to the maximum allowed distance in recent seasons, as coaches increasingly treat the dolphin kick as faster than surface swimming for a trained athlete.
The technique relies on core and hip strength most swimmers didn't train specifically a decade ago, and dryland programs have adjusted accordingly, with underwater-specific conditioning now a standard part of elite training blocks.
"If you can hold the kick to the legal limit and still be fresh at the surface, you're basically swimming a shorter race." — National swimming performance coach
Officials maintain the 15-meter limit is unlikely to change soon, but several federations have confirmed they're reviewing underwater camera footage more closely this season to ensure compliance at the margins.
