Nike NEXT%: Marathon running shoe so good it became controversial has been improved, company says

Two years ago, Nike unveiled what has been called the fastest shoe on the planet. It proved that claim last year, when it carried Eliud Kipchoge across the finish line at the Berlin Marathon, more quickly than ever before, not just breaking the world record but shaving a minute and 18 seconds off it all in one go. That shoe, the elite version of Nike's Zoom Vaporfly 4% Flyknit, even became controversial because it seemed to be just so good. The 4 per cent in its name referred to the extra efficiency boost it gave to its wearer – that in turn led to concern that the shoe was making its runners too fast, to an extent that almost seemed unfair. Now, Nike says it has made yet another step forward.