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Former South Carolina running back Marcus Lattimore signed a four-year contract with the San Francisco 49ers on Friday. Terms of the deal weren't disclosed.

The second of the 49ers' two fourth-round draft picks, Lattimore is feeling stronger each day as he continues his recovery from a serious knee injury.

Lattimore spoke to The Associated Press by phone about his rehab and said the most difficult part has been doctors and trainers slowing him down from overdoing things. Lattimore still believes he can be ready to play this fall, but is content to follow doctors' orders.

"I just want to train as hard as I can," Lattimore said. "But I understand why they want me to slow down."

Lattimore overcame a torn ACL as a sophomore to return to the field last season. His college career, though, ended for good against Tennessee last October when Lattimore dislocated his right knee and tore three ligaments. He had surgery a month later and declared for the NFL draft in December.

He trained in Florida for several months for the NFL scouting combine and South Carolina's pro day. Lattimore's future was one of the most discussed topics prior to the draft, several analysts wondering if he'd get picked at all and have to sign as a free again.

Lattimore said the work he put in was rewarded when the 49ers drafted him in April.

"It was one of the happiest moments of my life," he said.

Lattimore finished his college career as South Carolina's career leader with 38 rushing touchdowns.

Lattimore understands the importance of routine doctor visits, too. He said partnered with First Choice by Select Health of South Carolina to encourage teens and young people on regular medical visits, even without serious issues like Lattimore has had during his college career.

He said the relationships he built with family doctors as a child helped trust their guidance these past two year when he worried about his future.

"I didn't always know what to think when I was hurt," Lattimore said. "My doctors helped keep me straight."

Lattimore has a new set of issues to deal with in San Francisco. He's got a thick, new playbook to learn and a new home base to discover.

"It's a lot more expensive out here," Lattimore said.

He's talked extensively with new teammate, 49ers running back Frank Gore, who overcame two major knee injuries in college to become one of the NFL's top runners. Gore spoke with Lattimore during his injuries and served as inspiration for a comeback.

"It was great to finally meet him in person," Lattimore said. "He's been wonderful to me."

Dr. Greg Barabell, medical director of Select Health, said he was honored to have Lattimore helping get an important message out.

"Marcus can reach young people," Barabell said.

Lattimore's focus these days is getting back to the football field at a pace that works for his new team. San Francisco coach Jim Harbaugh has said he wants Lattimore to take a slower approach to returning.

"If he doesn't play this year, then he doesn't play this year. But I think if anybody can overcome what he's been through, it's him, Marcus Lattimore," Harbaugh said last month.

Lattimore appreciates the confidence and will go with the steadier, slower approach.

"I want to have a long, healthy NFL career," Lattimore said.