By Rieva Lesonsky

Many businesses, big and small, see Amazon as a huge competitive threat. But eMarketer reports there’s at least one industry that’s “impervious to Amazon:” the fitness industry.

The numbers back that up: According to the International Health, Racquet & Sportsclub Association, as of last year there were 36,540 health clubs in America, with more than 57 million members. Altogether in 2016, over 66 million Americans went to a health club of some sort and more than 5 billion (yes, billion) visits to health clubs/gyms/studios were recorded. The number of Americans with health club memberships has increased every year since 2005—as has the number of health clubs in the U.S. In 2016, revenue hit a record $27.6 billion, up 7% from 2015.

Randal Konik, an industry analyst from Jefferies & Company, told eMarketer Retail, “Health and wellness is a [long-term] trend. No longer are club memberships solely in the hands of affluent households.”

The clubs showing the most growth, according to eMarketer Retail, are the “low-cost and no-frills chains.” Also growing, which is a positive sign for small businesses and entrepreneurs, are the more “upscale niche boutique fitness studios,” which increased their revenue share of market from 21% in 2013 to 35% in 2015.

If you want to jump into the fitness industry, you can start your own business or buy a franchise. Remember, the niches are where the opportunities are—so much so that eMarketer Retailer says equity firms are interested in companies like Pure Barre and CorePower Yoga.

And don’t worry about competing for customers: According to the IHRSA, 19.3% of Americans belong to a health club, so there are plenty of potential customers for you to tap into.