It all started with just a meatball.

Mikael Lindnord was chowing down with three other Swedish athletes, trying to fuel up for the next morning's ordeal: a muddy 20-mile trek through the Amazon rainforest. The hike was one of the final two stages of the 430-mile Adventure Racing World Championship in Ecuador.

Then Lindnord, the captain of Team Peak Performance, tossed part of his lunch to a thin, scruffy street dog begging for food at his feet — and inadvertently enlisted a fifth team member, who they named Arthur.

Arthur and Team Peak performance in the Amazon rainforest. Credit: Krister Göransson/Peak Performance

Adventure Racing is an extreme sport that combines continuous hiking, trekking, mountain biking and kayaking over a successive number of days.

The team trudged for hours in the deep mud and steep terrain, but "the dog continued to follow us,” Lindnord says. When they stopped to eat and rest, they shared what they had with Arthur — even sacrificing their own meals for him.

“We checked our backpacks for more food and we found these two cans of soft food," Lindnord says. "We took one bite each and we just gave the rest to Arthur, because he was really exhausted."

Mikael Lindnord and Arthur taking a break. Credit: Krister Göransson/Peak Performance

Arthur kept up with them for the 20-mile hike, but the final leg of the race was a 36-mile kayaking route down a river. Organizers warned Lindnord that taking the dog with them in a kayak posed a safety risk, both for Arthur and the team.

But when the four athletes pushed their kayaks away from the river bank, Arthur swam out to follow them, desperately doggie-paddling to keep up. Lindnord grabbed Arthur and pulled him onto his kayak.

Arthur swimming next to Lindnord's kayak. Credit: Krister Göransson/Peak Performance

“You can’t reject a dog that had put in so much energy into you," Lindnord says. "It felt like he was one of the team members, and we didn’t want to let him down.”

The gesture prompted cheers from spectators watching from the banks.

“It was not easy [kayaking with Arthur]. He was shivering. We were also shivering, of course, but I had my Gore-tex jacket — so I put my Gore-tex jacket over him," Lindnord says.

Arthur also kept jumping into the river to chase after fish, forcing Lindnord to stop his kayak and pull Arthur back aboard. But the team, including Arthur, finished the race.

Team Peak Performance with Arthur. Credit: Krister Göransson/Peak Performance

Arthur made a trip to the vet before the team left South America; both the race and some old wounds left him weak and exhausted. But that's not where the story ended: Lindnord decided to adopt Arthur and take him back to Sweden.

Arthur arrives in Sweden. Credit: Krister Göransson/Peak Performance

Arthur is now being held in quarantine in Sweden. But as soon as he’s finished his time, Lindnord will bring Arthur to live with him.

Oh, and the name? The never-say-die dog is named after King Arthur, the British leader whose bravery became a legend.