There is a fear that grips all fighters, regardless of their talent, a sense of awareness that what was once their future has now become their past and that they are powerless to make a new beginning in a sport that favors youth, strength, and speed.

Having relentlessly tester their skill in combat for the whole of their professional lives, many fighters are hesitant, if not outright unwilling, to submerge themselves in the bleak abyss of retirement.

Not content with coaching, commentating, managing, or any of the more mundane aspects of MMA, great fighters will often attempt to push themselves beyond their physical limits by competing against opponents who have evolved to such an extent that they have rendered the abilities of their predecessors obsolete (see Coleman vs. Rua II and Shamrock vs. Diaz for excellent examples of this phenomenon).

Fueled by past glories that were all too fleeting and the adrenaline rush they received when their hand was raised in victory, former champions see retirement as a form of acquiescence; a giving in to the ravages of time and a personal admission of their inability to perform at an elite level.

Oftentimes, the acceptance of one's mortality is a bitter pill to swallow, so bitter in fact that a fighter would rather risk injury or public mockery than admit that he is no longer capable of duplicating those feats of endurance and youthful physicality that initially made him such an overwhelming success.

While such battle-hardened competitors run the stylistic gamut from the absurd (Tank Abbot, Ken Shamrock, Phil Baroni) to the truly legendary (Randy Couture, Wanderlei Silva, Matt Hughes), all suffer from a failure to comprehend that their best fights are behind them and that the future holds no promise of another title shot.

Perhaps the most recognizable adherent to this lamentable trend is none of than perennial fan favorite Randy Couture, whose less than stellar outing against Brock Lesnar proved that time is quickly catching up with the former champion.

At 45 years of age, Couture is not only the elder statesman of the UFC but also the oldest fighter in the world to be battling top ten heavyweights.

His compulsive desire to compete, coupled with his refusal to relinquish his championship hopes, has blinded Couture to the fact that his skills, which formidable, will not be enough to allow him to advance in the heavyweight division.

Rather than continue to subject himself to the ignominy of death, Couture should have retired after he annihilated Gabriel Gonzaga at UFC 74.

Had he made a clean break from MMA in 2007, Couture would have saved himself the trouble of a lengthy legal confrontation with UFC president Dana White, as well as a disappointing "comeback" loss to Brock Lesnar.

As it stands, Couture is currently entrenched in the purgatorial portion of his MMA career. Even if he were to defeat Antonio Rodrigo Nogueira at UFC 102, the chance of Couture receiving a title shot against either Frank Mir or Brock Lesnar are tenuous, at best.

While a victory against Nogueira would be a monumental achievement for Couture, placing him in a match for the UFC heavyweight crown would reek of both favoritism and sensationalism; there are already a number of lesser known (and less popular) fighters in line for a title shot, chief among them Cheick Kongo and future star Shane Carwin.

However, if Couture loses to Nogueira, as many predict he will, his MMA record will fall to 16-10 (which translates to a 63% winning percentage) and talk of another title shot will instantly become meaningless.

Still, Randy Couture isn't the only former champion who should seriously consider retirement. Known throughout the MMA world for his brutal fighting style and tireless work ethic, Wanderlei Silva has reached the point in his career where he can no longer compete at a championship level.

Boasting a record of 1-4 in his last five fights, Silva's position as resident headhunter in the light heavyweight division depends solely on his past achievements in PRIDE and not on his recent performances in the octagon.

In his bout against Quinton Jackson (a man whom Silva absolutely dominated in PRIDE), at UFC 92, Silva appeared sluggish, as if he were unable to keep up the ferocious pace that earned him the moniker "The Axe Murderer."

While such an uncharacteristic showing may not seems like a suitable reason for retirement, it should be remembered that, in recent years, three of Silva's four losses have come by way of knockout; the most memorable of which was a horrifyingly accurate head kick from Mirko Filipovic.

Despite the fact that Silva is renowned for his immense durability and dauntless fighting persona, such unforgiving punishment does nothing to help a competitor who has fought in over 40 MMA bouts and whose technique calls for him to charge headlong into battle, so as to provide fans with a memorable spectacle.

If Silva loses his upcoming match with Rich Franklin at UFC 99, he will have won only 17 percent of his past six fights, a record that will almost certainly spell his doom as a serious MMA competitor.

Yet, there are those in MMA who, unlike Couture and Silva, should unquestionably retire from the sport, not after their next fight, but immediately, so that they might save themselves from further professional embarrassment.

While many have argued that formerly dominant fighters like Matt Hughes, Mirko "Crocop" Filipovic, and Ricco Rodriguez should consider retirement within the years, perhaps the most eligible candidate for instant retirement is Mark "The Hammer" Coleman.

Notorious for his lack of conditioning when he fought as a heavyweight, Coleman appeared equally exhaustible during his 205-pound debut against Mauricio Rua.

A one-dimensional fighter when he was in his prime, Coleman's current fight game contains no dimensions whatsoever.

His trademark ground-and-pound tactics having been adopted by virtually every grappling-based fighter in MMA, Coleman should now be viewed as a MMA innovator rather than a promising competitor.

Much like the proverbial fish that refused to leave the familiar waters of his youth and learn to walk on dry land, Coleman has never evolved as a fighter; his present techniques are those of his mid 90's heyday, only now he is 44 years old and no longer able to dominate opponents with brute force alone.

An embarrassment to MMA (commentator Joe Rogan noted that in his last fight with Rua, Coleman looked like "a confused old man"), Coleman has not earned a victory over a worthwhile competitor since his May 2000 win against Igor Vovchanchyn.

Still, Coleman is not solely to blame for the farce that his career has become. It is obvious to those familiar with Coleman's rise to greatness that he currently is being exploited by Dana White for monetary gain.

For a man who supposedly wants to "protect" his fighters (as he protected Chuck Liddell by subtly forcing him into retirement after his April 2009 loss to Mauricio Rua at UFC 97), Dana White is using Coleman's past celebrity and drawing power to promote fights with the former heavyweight champion that have no business taking place.

His upcoming bout against a troubled Stephan Bonnar, while not as ubiquitously promoted as his second contest with Rua, should be the last time that Coleman appears in the octagon.

If, by some act of divine intervention, Coleman manages to emerge victorious then it is Stephan Bonnar, and not "The Hammer," who should consider the advantages of retirement.

While many fighters wisely make the decision to retire from MMA at the appropriate time, or else disappear into the vast network of lesser known MMA promotions, there exists a small minority of competitors who must be reminded that their period of greatness has come and gone.

Unfortunately, for such veterans, their unwillingness to accept their own limitations causes irreparable damage to their MMA legacy and ultimately works to undermine the integrity of the sport.

Perhaps there will always be fighters who don't understand that quitting while you are ahead is a far different thing from quitting altogether, because, as anyone who has ever been involved in MMA will tell you, quitting is never an option.