A step ahead? Nike's Vaporfly shoe changing marathon game

NEW YORK -- A type of shoe may play a significant role when sizing up the medal favorites for the marathon at the Tokyo Olympics this summer.

The Nike Vaporfly shoe has shaken up the sport since it was introduced four years ago. The shoe uses technology that some studies indicate gives athletes a four percent edge in energy efficiency.

The debate prompted World Athletics to significantly tighten its rules surrounding shoe technology.

Some consider the advances in the shoe market to be an exciting revolution. Others have called it technology doping that risks reducing marathons to a shoe competition.