Frank Gore is the NFL's 15th all-time career rushing yards leader, and first among active players, including Adrian Peterson, who was drafted just two years later.
Gore also charged for 1,000-plus yards in eight of his last 10 seasons, and was just 33 yards short of hitting the mark in 2015 at age 32.
But the Colts running back continues to hear doubts about his ability to produce.
"Believe me, I listen," Gore told the Indianapolis Star. "When I hear it, that’s when I attack my training.
"When I'm tired, I tell myself what the people are saying about me," he explained. "In that second workout when I'm saying, 'Man, I don't want to do this,' I remind myself, 'They're saying you're old. They're saying you're 33. They're saying you can’t do it this year.'"
Gore maintains that he is keeping himself in peak physical condition through a rigorous training regimen that includes two-a-days.
"I try to do two workouts three times a week," Gore said. "(In the second workouts), I do more agility, jump cuts, moves, working my feet in small spaces. Just trying to imitate like when I’m in the hole."
Gore also relayed that he also likes conditioning with younger players, which this year includes Bengals tailback Giovani Bernard, Vikings passer Teddy Bridgewater and fellow Colts teammate and cornerback Vontae Davis.
Gore, the 49ers' all-time rushing leader who averaged a career-low 3.7 yards per carry in his first season in Indianapolis, intimated that his roots also drive the running back on a daily basis.
"Man, I’m in the 'hood growing up, I’m living in this one-bedroom apartment with a single parent, with 13 people in there. Thirteen!" Gore recalled to the Star. "I knew that I wasn’t the smartest kid in school, but I knew that I had a way to get out if I did the right things in sports.
"It has a lot to do with how you grow up. Without the game, what would I be doing? That’s how I still approach it today. That's why, when I'm in practice, I'm always going hard. I've been blessed to make pretty good money over the years. But I still love the game and I want to keep showing people I can play."