CrossFit North Marin began with a group of buddies.

“We started out with some really good friends that came to our gym when we first opened, and then their really good friends came, and then their really good friends, so it was all kind of stemmed off our real close, tight-knit friendships,” explains Matt Barnes, one of four co-owners of the Novato, Calif., affiliate.

Barnes owns the box with his wife, Nicole, and fellow couple Travis and Amy Brackett.

“We’ve always kind of had the philosophy of ‘we don’t need a ton of people; we just need enough to pay our bills,’” Matt Barnes says. “(We) dreamt of this place that we can really get people together and hopefully change some people’s lives.”

One of those people is Arianne Miller, who used to be 100 lb. heavier. She started CrossFit in April 2011 with a free introductory class.

“The whole time I was so mad at myself … I couldn’t do any of it,” Miller says. “But all I said was, ‘All you have to do is show up.’ And every single day after that, all I did was show up.”