PORTLAND: Adidas is going barefoot.

The world's second-largest athletic company unveiled its first ''barefoot'' training shoe Tuesday. The Adipure, which will be in stores in November for $90, is designed to mimic exercising barefoot, but with the protection, traction and durability of wearing shoes.

Adidas, which is trying to expand in the US market where rival Nike dominates, is the latest athletic company to capitalize on the small but burgeoning market for so-called minimalist shoes. These shoes are a fraction of the $22 billion US athletic shoe industry, but sales of them have more than doubled in the past year. Those who wear the shoes say they force them to rely on the body's natural movements and avoid injury. Critics say the shoes cause muscle injuries that running shoes do not.

The theory behind the use of barefoot shoes is that the body is already optimally designed to move. Science backing up this theory suggests that traditional shoes inhibit that, which can sometimes cause the kinds of injuries that plague many runners.

Fans of barefoot shoes say they allow them to better use the body's natural motions and strengths. Some runners say they've also helped reduce injuries. Some weightlifters appreciate the ability of the shoes to lift without sacrificing their strength or stability to cushioning.

The barefoot culture has long had proponents, but it caught on widely in 2009 after publication of Christopher McDougall's book ''Born to Run,'' which explored the history and benefits of barefoot running. The movement got further attention last year when Harvard biologist and runner Daniel Lieberman published a paper in the journal Nature that concluded that running barefoot seems to be better for the feet, producing far less impact stress compared to those in traditional running shoes.