Running literally saved Marcus Cook's life. He used to weigh 489 pounds and now he weighs 245.
And every time he runs a race, he crosses the finish line with a cut out of what he calls, "Fat Marcus."
His inspiration to change and drop the weight was a friend, dying of cancer, who told Cook his lifestyle was going to kill him.
And so he had bariatric surgery in 2015, hit the gym and started running.
"My first goal was to do a 5K, then a 10K, then maybe I can do a small triathlon. I did a small triathlon," Cook said.
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Now his goal is to raise awareness.
"I'm proving every day you can do anything you want to do," he said.
That's exactly what Les Martin is doing.
He's the oldest runner in this year's half marathon.
He's 78 and has run more than 100 full marathons.
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He knows many people his age simply can't.
"I've got a lot of friends that they're just happy if they can walk out and get in their car," Martin said. "And me, here I am trotting around here on the hills in San Francisco. It doesn't get any better than that."
Neither Cook nor Martin are running for time on Sunday.
But they are running for the experience in one of their favorite cities in the world.
Get full details about the Rock 'n' Roll Half Marathon.