The downside is the Pro Bowl running back doesn't think he'll be ready for a full role in the season opener.

Asked yesterday if he thought he'd be 100 percent ready by Sept. 9 when the Chiefs open at Houston, Johnson said, "No, it'll take a little bit more than that."

"Obviously, coaches are going to do a great job trying to get me on track to where week two or week three of the season I can hit my full stride," he said. "I'm going to try pick up as fast as I can."

The 27-year-old Johnson signed a five-year contract extension on Tuesday, taking him through 2012. The deal includes a guaranteed $19 million and he will receive $27.7 million in the first three years of the extension.

After working out twice a day in Arizona while his teammates went through training camp in River Falls, Wis., Johnson appears to be in top shape.

Many think that taking off during camp and the first three exhibition games could prove beneficial after Johnson carried an NFL-record 416 times last year.

"What I know about myself is I've never been a fast starter coming out of the blocks in a season," he said. "I've always been — the last eight games is when I really turn it on. So I'm going to push myself as hard as I can to try to even it out."

Making big money will mean a bigger responsibility. Often in his first four years the 6-1, 235-pounder has been described as moody and uncommunicative. Those days are over, he said.

"It gives you a lot of responsibility," he said. "Whether you want it or don't want it, the responsibility is they made you the highest-paid guy in franchise history. You have to own up to it not only on the football field but in the community, and off the field. Those are the types of things you have to live with being the top-paid guy. You have to live with those responsibilities."

Family responsibility, he said, is what led him to hold out and demand big money after breaking the team rushing record two years in a row and emerging as one of the league's premier backs.

"It's all about family," he said. "When you have the ability and have the opportunity to be the top earner for your immediate family, for your generation, you've got to take the chance. It wasn't like the money was all for me, all to spend on me. I have a dozen little baby cousins. I have an uncle. I have aunts, I have grandmothers, I have nieces. In the future, I'm going to have nieces and nephews. That's for them. I've got to be smart as far as helping my generation, my unborn kids and their unborn kids. If I have the opportunity to take care of them for the long haul, I have to take that opportunity."

Now, with the contract out of the way, Johnson and the Chiefs can turn their attention to the season.

Though he expresses doubt, Johnson isn't ready to completely rule out being at full speed for the opener.

"It all depends on how I'm feeling. Of course, the adrenaline takes over," he said. "You're excited about playing. So we'll see. It all depends on what type of game we'll get ourselves into.