It is difficult to recognize with any certainty when a career begins to decline. After all, who knows the precise moment when reaction time starts to dull or the exact hour when a step becomes slower than it had once been? By the time most of us realize what we are seeing, the process is already hopelessly down the road.
Which brings us to LaDainian Tomlinson. To one of the greatest careers in NFL history.
It is impossible to say exactly when Tomlinson ceased being one of the game's elite running backs, but you might recall one of the last times you felt that way about him.
For it was on this weekend, three years ago, in another AFC Championship Game.
Going into that afternoon, Tomlinson was the NFL's reigning MVP. He was a two-time rushing champion on his way to a fourth consecutive Pro Bowl and had folks in San Diego calculating when he might pass Emmitt Smith as the NFL's all-time leading rusher.
And though no one was talking about it at the time, his best days were already behind him.
Tomlinson tweaked his left knee the previous week in a playoff victory against the Colts and got popped on the same knee on his first carry against the Patriots in the conference championship game. He stayed in for a handful of other plays, but the enduring image from that game is LT standing on the sideline in a parka as New England rolled to the Super Bowl.
Over the next two years, his rushing totals and yards per carry would drastically decline. He never made another Pro Bowl, and he was no longer Smith's greatest threat. He turned 30 in 2009, had a career-low 730 yards rushing and was no longer integral to San Diego's plans.
That a running back with so much mileage is still in the NFL is rare. That, at age 31, he reinvented himself with a new team in New York is amazing. That he finds himself with, perhaps, a final chance at a Super Bowl is, to him, a blessing.
"I've dreamed about winning a Super Bowl since I was 6 years old, growing up in Texas. Being a huge Cowboys fan and seeing the Cowboys win three Super Bowls in the '90s, that was when I was growing up and football was everything," Tomlinson said. "I always dreamt about having the chance to win my own championship. It would be anything and everything I could ask for in my career."
And few players have endured as much pounding to get this far. For instance, Tomlinson is fourth in NFL history in combined rushes/receptions. The three players ahead of him all reached the Super Bowl and combined to win four rings. And the three players behind him were also Super Bowl champs.
Which means Tomlinson stands alone in terms of longevity, production and lack of postseason success when it comes to running backs.
Much of that frustration, obviously, is beyond his control. But there is also no disguising the fact that Tomlinson has not been at his best when the calendar turns to January.
For his career, Tomlinson has averaged 85.9 yards per game and 4.3 yards per carry. Yet coming into this postseason, he had averaged 46.7 yards per game and 3.4 yards per carry in seven playoff games.
So maybe Tomlinson is the rare player who is actually telling the truth when he says a Super Bowl title would mean more to him than any individual honor. After all, he had a chance to return to the ranks of 1,000-yard rushers this season but told Jets coach Rex Ryan he would rather sit out a meaningless season finale in order to rest his legs for the playoffs.
"For me, it wasn't about getting 1,000 yards," Tomlinson said. "That's not why I came here. I came here to have an opportunity to win the championship."
In the process, Tomlinson has also sacrificed a bit of pride and ego to share the ball in the New York backfield with Shonn Greene. His 219 carries were the fewest of his career, but Tomlinson was back up to 4.2 yards per carry after dropping to 3.3 and 3.8 in his final two seasons in San Diego.
"In this system, you really have a chance to take a breath and get out of the game and keep going at it fully for four quarters," Tomlinson said.
"Usually when you are the No. 1 back and you take all the carries, you have to pace yourself throughout the game to make sure you have something left in the fourth quarter. With Shonn and I, we can just go full tilt every time we're in there."
He is not the same back of our memories. He does not run as fast or as far as we once recalled. He will likely never be a featured back again, and he might not even play beyond this season.
But this weekend, LaDainian Tomlinson has an opportunity.
Maybe he can't turn back the clock, but he can change the future.