Athletic shoe sales are soaring, at least on the Internet, the NPD Group reported this week.

Sales grew 21 percent to $5 billion in the year ending in April compared with the previous year, said NPD, which tracks consumer purchases.

Even with the rapid growth, e-commerce sales make up less than one-fifth of the $28 billion U.S. athletic footwear market, in which sales grew 5 percent year over year, the company said.

Online sellers have the advantage of offering the bigger assortments that consumers want, NPD said.

"Consumers are clearly looking for this bigger online assortment each year, and some retailers are working really hard at maximizing space to include as many style offerings as possible," said Marshal Cohen, NPD’s chief industry analyst.

NPD found that online shoe shoppers care more about brand, style and price than in-store shoppers. Shoppers in stores put more emphasis on comfort. Men tend to buy more of their athletic shoes online than women.

A higher percentage of the footwear bought online was on sale – 53 percent – compared with the share of on-sale footwear bought in stores, 47 percent. Even so, the average selling price of online shoes during the year, $54.63, was higher than the $42.16 average for shoes sold in brick-and-mortar stores.

"Sports sales have been growing faster online than other categories including apparel, fashion footwear, and fashion accessories," Cohen said. When it comes to buying athletic footwear, "shoppers shop online for better deals, but they are willing to trade up to higher-priced products."

lorraine.mirabella@baltsun.com