Matt Damon's Surprise Entry in Miami Triathlon

By Stephen M. Silverman

10/06/2008 at 09:45 AM EDT

All that running in the Bourne movies has paid off for Matt Damon: Sunday morning he participated in the Escape to Miami Triathlon.

"'My brother talked me into it," Damon, 38, told the Miami Herald. Brother Kyle Damon finished Sunday in 27th place, with a time of 2:23:40.

PEOPLE's reigning Sexiest Man Alive, meanwhile, ran in a team that also included his stepfather Jay Jones and family friend Barry Hetherington, and was met at the finish line by wife Luciana Bozán Barroso and 7-week-old daughter Gia – and a lot of delighted fans who hadn't expected to see Damon in the race.

Damon's time for his 6.2-mile portion of the challenge was 59 minutes, 54 seconds. "I knew I was in trouble when the old guy with the oxygen tank passed me," he joked.

Damon got into the race, he said, because, "'I was doing this movie this summer The Informant where I had to put on all this weight, and my brother told me, 'October 5, save the date.' "

Besides, he said, ''I've got to get in shape for the next thing I'm doing."

RELATED GALLERY:
• See Matt's SEXIEST moment!
RELATED ARTICLE:
• Get inside J.Lo's triathlon training after twins