The St. Louis Rams, who slipped into the playoffs at 8-8, arrived at the Georgia Dome on Jan. 15, 2005. Steven Jackson, then a Rams rookie and the understudy to Marshall Faulk, remembers the night: “Like the second play of the game, Michael Vick runs to the left for the sideline. He thinks he’s bottled in and skirts for 70.”

Actually, it was the third play, and Vick’s gain was for 47 yards, but you get the gist. The 47-17 loss the Falcons inflicted on Jackson’s Rams still rankles. That galling Saturday remains the last time he has taken part in a playoff game.

Eight 1,000-yard seasons later, Jackson is a Falcon. He signed here as the presumptive replacement for Michael Turner, who had been the Falcons’ feature back since 2008. Three times a Pro Bowler, Jackson has been a very good player for nearly a decade, but he wants what all players, even bad ones, want. He wants a championship.

Jackson rushed for 10,135 yards as a Ram. If you’ve had him on your fantasy football team, you’ve come to appreciate him. If not, probably not. It’s not easy to gain 10,135 yards in utter obscurity, but St. Louis was so far down the past eight seasons it might as well have been Siberia.

Said Jackson: “It’s one of those things where someone reads your stats or sees you make a one-handed catch and it’s like, ‘Wow.’ And I’m like, ‘I’ve been doing this for a long time.’”

He has. He was drafted out of Oregon State in 2004. (He’s from Las Vegas, which coincidentally is the hometown of Gerald Riggs, the Falcons’ all-time leading rusher.) Jackson will turn 30 next month, and his big body — he’s 6-foot-2, 240 pounds — has borne the brunt of 2,395 NFL carries. As a concession to wear and tear, the new Falcon has given up gluten.

“The one thing I kept hearing is (about) your ability to recover week to week,” he said. “When you first come into the NFL, you’re ready for Wednesday practice. As you get older, it takes longer and longer throughout the week to get ready for the next game. I’ve learned through my research that if you go to a gluten-free diet, it helps with inflammation and it helps you recover. Things don’t linger as long.”

What did he stop eating? “The biggest thing is bread. I was never a Big Mac guy, but I love pizza. My mom is from the South, so you’re talking about cornbread. A lot of things that I grew up loving, I had to give up.”

Does he feel different? “Actually, I do. I feel the effects from practice to practice. I feel my legs are not heavy. I feel like I have strength.”

Falcons general manager Thomas Dimitroff is a vegetarian of long standing, but his conversion wasn’t without regression. After a few meatless weeks, he yielded to temptation and made for McDonald’s. Sitting alone in an empty football stadium, Dimitroff scarfed down a Big Mac and fries, feeling both satiated and ashamed.

“I have a very similar guilt trip,” Jackson said. “I had a pizza three weeks into the diet. I felt like a total slob. I felt like I let myself down.”

Ah, well. It’s early yet. With a little practice, he might make the leap to vegetarian or, as is the case with new Falcons teammate Tony Gonzalez, to out-and-out vegan. Laughing, Jackson said: “Give me a couple of years on that one.”

If there’s a takeaway from Jackson’s dietary modification, it’s that he’s enough of a professional to do what needs doing to maintain a standard of personal excellence. “My outlook on life is, we’re going to have to adapt to things as we get older. The body and the metabolism slows down. You’re going to have to rely on your knowledge more than your physical attributes. Why wait until you’re forced to do it? Why not start it now so it’s not so hard?”

Jackson prides himself on being a three-down back, which not many are anymore. (Turner wasn’t.) Jackson can catch — 407 career receptions for 3,324 yards — and block. “The running backs I grew up idolizing were all three-down backs, like Thurman Thomas and Marcus Allen. You name it, I studied that guy. I just love the game of football.”

The Falcons got their money’s worth from Turner, who left as the best free-agent signing in team history. Jackson has the potential to be as good or better, and he has spent 8 1/2 years waiting to grace another postseason. He didn’t come here to take early retirement. He came to achieve one long-simmering goal.

“A successful season for me,” Jackson said, “is getting to the playoffs and getting to the Super Bowl. If it doesn’t happen, I want to make sure I’m not the reason we fall short.”