It is a fact of life that age and circumstances catch up to all athletes at some point.
Some have greater staying power than others, but eventually, even the best of drivers have to realize they will never be relevant again. They may show flashes of their old winning ways, but they'll never be seriously mentioned in championship conversations or be consistent front-runners from week to week.
Occasionally they hang on longer than they should, a situation that happens in NASCAR to a sometimes embarrassing extent. No one likes to see a former championship-caliber driver puttering around the back of the pack.
For the most part, the drivers on this list aren't at that point, and I'm not saying they should hand over the keys right away. I'm just saying I don't see them being considered as top drivers in the sport for the rest of their careers.
A few of the drivers on this list are aging veterans who were recently considered to be some of the top drivers in the sport, while others are younger drivers whose careers I believe are on the downswing.
I'm sure that some will disagree with my analysis, and I might be proved wrong if one of these drivers has a career resurgence. I just don't see it happening.
After he left Roush Fenway Racing at the end of the 2005 season, Jeff Burton's career was supposed to be over.
Burton proved the naysayers wrong over the next five seasons, winning four races, making the Chase four times and averaging over 16 top-10s per season.
This season, things have gone awry for Burton in a major way and he is on the brink of another career crisis.
After 21 races, Burton is 24th in the standings and has zero top-10s. Every other driver in the top 30 has at least two top-10s.
I'd like to think that Burton can turn it around again, return to his winning ways and challenge for championships. But it's 2011, and at 44 Burton is six years older than he was at the beginning of his first career resurgence.
The good news is that Burton and sponsor Caterpillar both agreed to multi-year contract extensions earlier this season, so at least his ride isn't in immediate jeopardy. However, with results like he has had in 2011, you have to wonder how much longer Burton will be able to put forth maximum effort without a dramatic turnaround in the results on the track.
Burton is one of the elder statesmen among NASCAR drivers and is well-respected among his peers, but, sadly, it seems his days as a top-level driver are over.
In 2009, Mark Martin had a storybook season, as he returned to full-time racing for the first time in three years. He recognized how special his season was, savoring each of his five wins as he fell just short of winning a championship yet again.
Martin is now 52 years old, winless over the last year and a half. He hasn't been terrible in 2011, and in fact he nearly won at Dover a few months ago.
But things just aren't the same as they were during that magical 2009 campaign.
Martin has fallen to 15th in the points during his lame-duck season at Hendrick Motorsports. With just one top-5 to go along with six top-10s, neither the speed nor the consistency has been there for Martin this year.
A 40-time winner in the Cup series, Martin is a free agent following the season. It is unclear where he may end up, or even whether he desires to race full-time.
Martin has had a long and successful career in NASCAR and he is good for the sport. He is a gentleman on and off the track as well as a great mentor for younger drivers.
But unfortunately, the chemistry just hasn't been there for his No. 5 team since 2009. I really like Mark Martin and I hate to say this, but it looks like his days of competing for championships are over.
I will admit that Bobby Labonte is rather low-hanging fruit for an article such as this. It's been 11 years since his only title, and no one expects him to win another. Labonte has had just nine top-10's in the past five seasons and hasn't won a race since 2003.
However, I included him because bigger and better things were expected of him in 2011.
Labonte is in the best equipment he's had since leaving Joe Gibbs Racing following the 2005 season. But he's failed to do much with it.
More than halfway through the season, Labonte is 29th in the standings, has led just six laps, and has two top-10s and one top-5 (a fourth-place finish in the Daytona 500). That doesn't even measure up to the relatively mediocre results of Marcos Ambrose in the No. 47 car last year (26th in the points, 84 laps led, two top-5s and five top-10s).
It may well be time for Labonte to turn over the keys to a younger driver with a brighter future. He's gotten his one last good chance to show the fans what he has left in the tank, and it's running pretty near empty.
It will be sad to see such an accomplished and well-respected driver go, but the last thing NASCAR needs is another Kyle Petty hanging around 10 years past his welcome.
At 35 years old, Jamie McMurray is much younger than the previous drivers on this list, but I think his best days in NASCAR are already behind him.
After an incredible run in 2010 that saw McMurray win the Daytona 500 and notch a career-high three victories (though he did fall short of the Chase once again), the current season has been an unqualified disaster for McMurray.
The Earnhardt Ganassi driver has fallen on hard times and is on track to have his worst season ever.
McMurray has a mere three top-10s in 2011 and just notched his first top-5 with a fourth-place run at the Brickyard two weeks ago. He sits 27th in the standings, one position lower than he has ever finished a season.
McMurray's career has been one of unfulfilled promise. Twice in his career, McMurray has had sky-high expectations.
The first time was following a win in his second-ever Cup race and a promising rookie season in which he finished 13th in the standings. But over the ensuing seasons McMurray never was able to make the Chase. A move to Roush Fenway Racing failed to yield improved results.
Expectations were again raised for McMurray after his promising 2010 season, but he has failed to deliver as hoped for yet again. The Chase has narrowly but consistently eluded McMurray throughout his career—he's finished 11th through 14th four times—but in 2011 the wheels have really come off.
Time is very close to running out for McMurray to become an elite driver, and I just don't think it will happen. I like McMurray as a person and he certainly has a great deal of driving ability, but for whatever reason he seems unable to break through to the top echelon of drivers. I don't expect McMurray to ever fulfill his considerable promise or even to repeat what he did last year.
At 27, Brian Vickers is easily the youngest of these five drivers. As such, I probably stand the greatest chance of being wrong about his future.
But there are compelling reasons to suspect he will never truly be a top-level driver, and quite possibly never win another race at NASCAR's top level.
First off is the fact that Vickers has driven for one of the top organizations in NASCAR, Hendrick Motorsports, and failed to do anything notable—other than wreck then-teammate Jimmie Johnson en route to his first career win at Talladega.
After leaving HMS, Vickers struggled with the fledgling Red Bull Racing before having his career year in 2009. He gained the second win of his career, made the Chase and scored a career-high 13 top-10s.
However, his 2010 season was cut short by blood clots, and although he is once again healthy in 2011, the results have been disappointing. Vickers has just five top-10s and sits a lowly 28th in the standings. He has yet to lead a single lap all year.
But that's not his biggest problem. The future of Red Bull in NASCAR is up in the air, and it's not even clear whether Red Bull Racing—or whatever it may become—will field teams in Sprint Cup competition in 2012.
If Vickers needs to find a new team, I have a hard time imagining him landing anywhere that would afford him a good chance to win. Stewart-Haas and Gibbs are possible landing places, but I doubt either of them would sign a driver with a track record as spotty as that of Vickers.
Sure, Vickers has considerable ability as a driver. But in NASCAR you typically get only so many chances, and as happened in the similar case of Casey Mears, the days of Brian Vickers being relevant on a top team are over.