LONDON (AP) — On a weekend morning in the fall of 2004, 13 runners lined up in a London park for an informal race — unaware they were taking the first steps in what would become a global movement. Paul Sinton-Hewitt had simple ambitions: to provide a free, weekly 5-kilometer (3.1 mile) run open to anyone.

“I didn’t know who was going to join me on that day,” Sinton-Hewitt said. “I didn’t care how many people came. I would be on the start line every single week for the rest of my life and I would help people to run.

” Parkrun — as it became known — has far exceeded any vision he had, marking its 20th anniversary on Saturday with runs now held in more than 2,500 locations, including 25 prisons, in nearly two dozen countries. More than 10 million people have participated in at least one parkrun and the organization has recorded more than 100 million finishes. “We’re the smallest that we will ever be,” Sinton-Hewitt said.

“In 20 years time when we come back and have this chat again those numbers are going to be minuscule. So it’s a bizarre thing.” The feel-good fun run is credited with changing countless lives, getting people up and moving, motivating them to come back week after week and nurturing lifelong friendships.

Testimonials have come from couch potatoes to people who reversed diabetes and stopped drinking to inmates who found an escape while serving time. The World Health Organization has endorsed parkrun for offering an accessible way to b.