We went to Athleta and saw why the brand is one of Gap's secret weapons

Athleta is about to expand across America in a big way.

Gap Inc. announced earlier this week that it will be opening around 270 Athleta and Old Navy stores in the next three years, while closing 200 Gap and Banana Republic stores in that same time period.

Athleta, Gap's athleisure brand, has thrived while many brands have struggled in the difficult retail climate of recent years. The company said that it expects the openings to bolster Athleta sales to over $1 billion in the next few years.

Athleisure - the trend of wearing activewear in everyday life - has become the apparel of choice for many Americans over the last several years. As of 2016, activewear had become a $45.9 billion market for retailers, according to data from the NPD Group.

We took a trip to Athleta's Fifth Avenue store in New York City to see firsthand why Athleta has become one of Gap's most successful brands.