By Andy Clendennen
RealTime Fantasy Sports

It happens to all of us: We don't run 15 miles as fast as we used to, or our legs tire on our jump shots midway through the second quarter instead of the fourth, or we even forget how to mix our favorite drink just the right way, every single time.

In short, we get old.

For most of us, it doesn't matter - we're a bunch of has-beens/never wases. But for the elite athlete, the professional athlete getting paid millions a year, hitting the wall hurts physically, mentally, and eventually, financially.

Nowhere is that more true than in the world of the running back. You've heard it before, you've read it before, and you will continue to for as long as you play fantasy football: When a running back hits 30 years old, it's all over.

And that's true about 95 percent of the time. In the following space, we'll examine the history of some running backs and their respective declines, and we'll discuss the several running backs hitting that red-flag area this year. And for the sake of argument, we won't limit ourselves to just those turning 30 - we'll include some 29 and some 31-year-olds, because it's difficult to pin down exactly the age of the decline.

So first, a few historical case studies:

Priest Holmes burst onto the scene in 2001, when he was 28 years old. That year, he carried the ball 327 times for 1,555 yards and eight touchdowns, and that was the first of three tremendous years the likes of which we've rarely seen from a running back. From 2001-2003, Priest averaged 320 carries, 1,530 yards and 18.6 touchdowns. But that's just on the ground. He added an average of 69 receptions, 659 yards and two touchdowns through the air. That's an average of 390 touches a year.

But in 2004, Holmes turned 31. He started off right where he left off the previous three seasons, with 14 rushing touchdowns and nearly 900 yards through the season's first eight games. Then, disaster. An injury ended his '04 campaign, and in the next two seasons combined, Holmes played a total of 11 games and had 165 carries.

Shaun Alexander also had a terrific three-year stretch, from 2003-05, when he was 26, 27 and 28 years old. During that span, he averaged 350 carries, 1,670 yards and 19 touchdowns. He wasn't as prolific as Holmes out of the backfield, with an average of nearly 27 catches per season, but his overall touches were comparable at 377.

Then came 2006, when he turned 29. Alexander got hurt and averaged 3.6 yards a carry with seven touchdowns in 10 games. In 2007-08 (ages 30-31), he combined for 218 carries and a paltry 3.4 yards per rush. He went from scoring 27 TDs at age 28 to scoring 7, 4 and 0 at the ages 29, 30 and 31.

Finally, Marshall Faulk had a four-year stretch of dominance, from 1998-2001, when he was 25-28 years old. During that span, he averaged 356 touches, both rushing and receiving, and 17 touchdowns.

Then, at age 29 in 2002, he rushed just 212 times, didn't reach 1,000 yards, and scored just eight touchdowns on the ground. The following year, at age 30, he averaged 3.9 yards per carry. At ages 31-32, he had a total of 839 yards rushing and just three touchdowns.

Those three were at various times in their career called the best running backs of their generation, and they hit the wall, hit it hard, and never recovered.

While they all have one thing in common at the time of their decline - their age - the discerning eye will also notice another corollary - their average number of touches in the previous seasons. Holmes: 390; Alexander: 370; Faulk: 356. That's a lot of big linemen/angry linebackers going high-low, taking out the knees, whatever. And that doesn't even include the times (admittedly few, but just as bone-crunching) that the running backs blocked, or were blocked away from the play.

So, without further ado, here are your candidates, given their age and past workload, for a potential downfall this year.

First, obviously, is the one I like to call the greatest running back of all time, LaDainian Tomlinson. Of course, to retain that moniker, he'll have to buck the trend of aging running backs and show that last year was an anomaly.

L.T. enters the season at (cue Gargamel's theme) 30 years old.

Even though last year, when he was 29, was solid from a fantasy perspective, with 1,110 yards and 12 total touchdowns, people were quick to jump on the "L.T. is dead, long live L.T." bandwagon. And with good reason - while those numbers might be good for a Brandon Jacobs, Marshawn Lynch or Chris Johnson, those are decidedly not the numbers L.T. - and his fantasy owners - are accustomed.

Will he bounce back? All mancrush aside, the numbers say no. He's had fewer than 300 carries just once in his career, and that was last year at 292. And after just eight NFL seasons, he's No. 14 all-time in number of touches. For his career, he's averaging more than 395 touches a season.

However, he is LaDainian Tomlinson - his work ethic is nonpareil, he's had a healthy offseason, and his pride won't let him rest on past accomplishments. He's just three years removed from the greatest season a running back has ever had, with 2,300 yards and 33 touchdowns. Plus, the Chargers slapped Darren Sproles with the franchise tag and either did or did not entertain the thought of trading L.T., so he could be back with a vengeance this year.

The guess here is that he has at least one more L.T.-like season in him (1,500 yards with 15-18 TDs). But we wouldn't be surprised either if Sproles and Jacob Hester become larger parts of the San Diego offense, relegating Tomlinson to 20 carries a game. While it might keep him fresh for the duration of the season and playoffs, his overall numbers will suffer accordingly - especially if Hester gets the majority of third-and-goal carries.

In a situation similar to Tomlinson, Brian Westbrook - also turning 30 - didn't get as many props as he should have in 2008. He only totaled 1,338 yards and 14 touchdowns. But he played in 14 games, and people seem to focus on the two he missed. And, it was a very un-Westbrook-like performance, on the heels of his '07 campaign when he had more than 2,100 yards. He's averaged 324 touches over the previous three seasons and has seen his yards per carry drop from 5.1 to 4.8 to 4.0 over that same span. Plus, he's never played a full season in his career, and as you get older, those injuries become more frequent and take longer to heal.

Will he be able to rebound? Perhaps, depending on a couple of rookies and how he comes back from ankle surgery performed late in the offseason. First, Mizzou first-rounder Jeremy Maclin is a speedy addition to the receiving corps, depending on how fast he picks up the offense. A home-run threat every time he splits wide, the addition of Maclin could open some running lanes for Westbrook just a bit. And with Westbrook, who showed flashes of his old self last year, just a bit is all he'll need. The second impact rookie is LeSean McCoy. The Eagles didn't draft - and pay - McCoy to sit on the bench and watch. He could play a role similar to Sproles, garnering about 10-15 carries a game, thus decreasing the workload - and overall production - of Westbrook.

While Tomlinson and Westbrook are odds-on favorites to bounce back, or at least not decline any further just yet, Larry Johnson is just a mess.

He enters 2009 at 29 years old, is on a horrid team with no receivers, a one-year wonder at quarterback (anyone out there remember Don Majkowski?) and his team has lost total confidence in him. And while he doesn't have the average number of touches over the previous years as Westbrook or Tomlinson, he DOES have something they don't - a 416-carry season on his resume. Conversely, he has just six seasons in the NFL, and in only two of them did he eclipse 200 carries, so he has THAT going for him, at least.

But while most players mature, Johnson is treading dangerously close to Lawrence Phillips territory. We've seen Johnson spit in women's faces, allegedly slapped them around, and acted out and pouted in defiance of his head coaches.

Now, the Chiefs have a new quarterback, a new GM, a new coach, a new stadium (OK, partially new) and a new tight end, merely replacing one of the top three or four tight ends in history. Johnson has a bad attitude, a bad situation, no backup, no help, and a team that will be losing the majority of its games - even in the weak AFC West, which could be the weakest conference in the NFL, even with the Chargers.

It is possible Johnson could score 10+ touchdowns again. With Tony Gonzalez gone, L.J. becomes the odds-on favorite to get the ball most of the time inside the 10. (Although, keep in mind that quarterback Matt Cassel had 73 rushes with a 3.7-yard average, and scored twice last year.) You'd think that Johnson could get 1,000 yards by default, but I wouldn't bet on it. This team is bad - like Detroit Lions bad - and may not be in a position to run the ball much after the second quarter.

Thomas Jones is entering the 2009 season at 31. So what, you say? He had a spectacular 2008 - all he did was rush for 1,312 yards and piled up 15 total touchdowns, great numbers for any No. 1 fantasy running back not named Adrian Peterson. But again, refer to Priest Holmes. There does come a time, occasionally, when a 30-year-old will make an impact, but at 31 the thrill is gone. Working against Jones this year is the fact that the Jets traded up to acquire Shonn Greene, so the Jets' brass can see the writing on the wall as well.

Finally, Jamal Lewis - much overlooked - comes into the 2009 season at 30 years old. He also had a somewhat decent 2008, rushing for more than 1,000 yards (barely, at 1,002), but scored just four touchdowns. But here are two key numbers when considering Lewis - he's rushed for less than 1,000 yards just once in his eight-year career, and he's played at least 15 games in seven of his eight seasons.

But, here's a third key number for Lewis: 248, as in, his weight. He's a big boy. And big boys wear down quickly - see Bettis, Jerome (yes, yes, I know - he scored touchdowns well into his early 30s, but his yardage was Brad Baxteresque - decidedly not the numbers you want from a No. 1 running back).

If guys like Emmitt Smith and Marshall Faulk had trouble maintaining their status as impact players beyond age 30, just think if they lugged around an extra 30 pounds or so, and imagine how their downfall would have been hastened. And with James Davis waiting in the wings, we could have seen the best of Lewis that we're going to see.

The following running backs will also be 29 or older on opening day this NFL season (not all 29-year-olds are listed, just the ones who could/should be drafted in your fantasy league:

Ladell Betts, Correll Buckhalter, Warrick Dunn, Justin Fargas, Kevin Faulk, De'Shaun Foster, Earnest Graham, Edgerrin James, Rudi Johnson, Lamont Jordan, Deuce McAllister, Maurice Morris, Sammy Morris, Michael Pittman, Dominic Rhodes, Chester Taylor, Fred Taylor, Derrick Ward, Kenny Watson and Ricky Williams.

And as we mentioned, touches in the previous seasons could be just as important when determining a runner's future. So with that in mind, here is a list of running backs with more than 500 combined rushing attempts in 2007-08:

Clinton Portis (642), LT (607), Jones (600), Lewis (577), Adrian Peterson (576), Willie Parker (531), Lynch (531), Westbrook (511), LenDale White (503), Frank Gore (500) and Ryan Grant (500).

Contributor Andy Clendennen previously worked for The Sporting News web site, for which he wrote a weekly fantasy baseball advice column. In addition to The Sporting News, Andy has worked as a sports writer for 10 years, in St. Louis and in Colorado.