Colorado coach Brian Kula, speed trainer for 49ers running back ...

Being a star running back in the NFL isn't easy. You can ask plenty of the greats who have blessed our league, from Bo Jackson to Emmitt Smith to Adrian Peterson.

If there is one person who understands the grit and grind that comes with being a premier running back in this league, it is San Francisco running back Christian McCaffrey. 

Ever since high school, McCaffrey has been known as a running back who can sell out arenas just based on his raw talent alone, and there is one coach who has been with the star every step of the way -- coach Brian Kula. 

Kula says he's known McCaffrey since he was an "ankle biter" growing up in Colorado.

"We usually start him here on our turf, and we do some of our activation and mobilization," said Kula while giving Griego a tour of his facility in the southern part of the Denver metro area.

Kula Sports Performance in Centennial is a sanctuary for athletes of all levels to get faster and stronger over the course of their careers.

Brian and his team have worked with many professional athletes, but arguably his most well-known is McCaffrey. The running back was 13 years old when he met the trainer at a football camp back in 2009. 

"Pretty focused young man, even at a young age," Kula recalled. 

Kula went on to coach the young star in football and track at Valor Christian High School in Highlands Ranch. 

"He's one of the best athletes I've ever seen," Kula said. "You know, even in high school, seeing what he did and watching him through college at Stanford, and it's just not been a surprise."

Kula also believes McCaffrey's focus on becoming the best never waivered. 

"The preparation and taking things seriously and locking down on all the things that mattered ... diet, nutrition and sleep and just paying attention to everything, separates him from a lot other athletes," Kula expressed. 

Kula also touched on how tough McCaffrey's training regiment is and why they emphasize on making the sessions tough for him.

"Well, he's demanding, and he's got super high expectations, and sometimes if those aren't met in a training session, it can be a rough training session," Kula said. 

He added, "You know, I think he's made me a better trainer. I show up and have to be ready to go for him. We pivot and do a lot of different things every season, according to what he needs, and he's very involved in what we do. So it's not always the easiest thing but it's definitely rewarding and fun." 

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This year, McCaffrey was nothing short of spectacular after leading the NFL in rushing yards with 1,459 yards on 272 carries and 14 touchdowns for the regular season. He was also selected for the NFL All-Pro Team, won Offensive Player of the Year and received the second annual Jim Brown Award. 

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