EDEN PRAIRIE, Minn. Vikings running back Adrian Peterson and Tennessee Titans back Chris Johnson have been linked since Johnson broke out with a 2,000-yard season in 2009.The two dynamic backs have been judged against each other, while being seen as the league's two best rushers the past three seasons. The comparisons continued this preseason when the two signed rich new contract extensions.There are few similarities between Peterson and Johnson now though with eight regular season games in the books. Peterson is putting together one of his best seasons as a pro and Johnson has struggled since returning from a holdout.For Peterson, his numbers this season don't have to do with living up to his lofty seven-year, 100-million contract extension. The groundwork for his success was laid in the offseason."It all came before I got my deal, how I prepared in the offseason," Peterson said. "When I left last year, I had the mindset that, Hey, I want to make sure that I'm going to be the best when this year rolls around.' So I trained my butt off."To be honest, during the offseason I wasn't thinking about a contract. I was thinking about just playing my current contract out and seeing what happens after that. So, my focus was working, grinding and then it will show on the field. That's pretty much what's going on now."Peterson's 798 yards rushing are second in the league to Buffalo's Fred Jackson's 803 yards. Peterson's 10 touchdowns are tied for second in the league with Philadelphia running back LeSean McCoy and trail only Detroit receiver Calvin Johnson's 11 scores.Meanwhile, Johnson has averaged a career-low 3.0 yards-per-carry and has just 366 rushing yards and one touchdown. Due to Johnson's struggles, Tennessee has the fewest rushing yards (560) in the league this season.Johnson held out and missed much of the preseason before signing a four-year, 53-million extension with 30 million guaranteed. He has added 31 catches this season, but has topped 100 yards on the ground just once. Less than two weeks after Johnson signed his deal, Peterson trumped Johnson's deal with the richest deal in NFL history for a running back, which came with 36 million in guaranteed money.Coach Leslie Frazier wasn't worried about Peterson's play being affected by the big contract."I haven't seen anything in Adrian's play along the way that would say he wouldn't be able to live up to that contract," Frazier said. "He's been a great player, as we all know, for quite a while, throughout his history in the National Football League. The only thing you look at is just the history of running backs and what happens with running backs."Peterson, 26, is tied to the organization through the 2017 season. The belief exists that running backs deteriorate once they get past 30-years old. While Peterson has taken a lot of pounding in his five NFL seasons, his work ethic might help him survive past 30.Peterson's offseason work has him on pace for post the second-best rushing total of his career. His career-best 1,760 yards rushing was set in 2008. He's also on pace to break his career best of 18 touchdowns set in 2009."It was just the offseason work," Peterson said. "You're going to get what you put into it. I made sure when my training stopped that I was satisfied. I knew that, hey, god-willing I'll stay healthy, we're able to gel more as an offense, offensive line and I'm going to be productive."Peterson also put more of an emphasis on building his speed this offseason, which surprised Frazier."He's probably the fastest guy on our team and one of the fastest in the league, if not the fastest, and he was saying he wanted to get faster," Frazier said. "And it seems that he has. He runs harder than he ever has and seems so much more determined than I remember him being."Peterson is now hoping he can put his speed to use more in the passing game. He has 16 catches this season far behind his career-high of 43, but he had five catches for 76 yards and a touchdown receiving in Minnesota's 24-21 win at Carolina before last week's bye. He took two consecutive passes accounting for all of the 39 yards on a scoring drive against the Panthers.Getting Peterson involved in the passing game has been talked about in Minnesota for years. As always, he feels he's ready for the work."Throw the ball to me and then I can do something with it," Peterson said. "A lot of people like to say, He's not a good receiver.' Or this, that and the other, but you got to put the ball in my hands. You know? If it doesn't, then hey whatever, I'm still going to do my job as far as being productive in the run game. If they do throw the ball to me, then I will be productive in the pass game too. It is what it is. I don't complain about too much."He's certainly giving the Vikings little to complain about, even as a 100-million player.Herrera to miss Monday night: Right guard Anthony Herrera missed practice again Friday and Frazier said Herrera would be out for Monday night's game at Green Bay. Herrera missed the Carolina game with a lateral collateral ligament injury in the same knee which he tore his anterior cruciate ligament last season and had surgery on during the offseason.Frazier said Herrera will be reevaluated next week and he doesn't think it's going to have any long-term effects."He's still making progress, but not to the point where we could say, OK. Let's go out and try to do something.'," Frazier said. "They haven't cleared him to try and go out and practice. So we just have to wait."