Despite being one of the most consistently productive players in the NBA for over a decade, Mavericks forward Dirk Nowitzki seemed to go relatively under the radar for most of his career. Maybe it’s just because he wasn’t in Los Angeles or New York, but Nowitzki’s standout play didn’t receive much national attention until he led the Mavs to an upset over the superstar-stacked Miami Heat in the 2011 NBA Championship. That's a shame because, at 34-years-old, Nowitzki has already begun the slow descent out of his prime. The drop off isn’t pronounced just yet, but recurring health problems have contributed to both his playing time and points per game declining over the last three seasons.

by AMBER LEE (follow her @blamberr)

The Chargers took a chance on tight end Antonio Gates, an undrafted free agent out of Kent State, in 2003 and it paid off in a big way. Not only has Gates been one of the most dominant players at his position over the course of his career, he’s widely considered one of the greatest tight ends of all time. From 2002-11, Gates averaged 9.25 touchdowns and 925 yards per season, with an average of 13 yards per catch and just two fumbles—total—over that span.

Unfortunately, Father Time is finally catching up to their once unstoppable superstar tight end. Injuries have become a nagging problem for Gates, who hasn’t played a full season since 2009. His total yards have declined over each of the last four seasons and injuries have led to some unwanted weight gain for the 32-year-old tight end.

PGA golfer Tiger Woods was perhaps the most prolific athlete of a generation when the news broke that he had crashed his Escalade into a tree outside his home in November 2009. The scandal that ensued was one of the most salacious to ever hit the sports media, and the tabloids were absolutely relentless.

Bears linebacker Brian Urlacher spent the greater part of the last decade as one of the most dominant and feared players at his position in the NFL. Aside from the 2004 season in which he missed seven games due to injury, Urlacher played every single game for the bears between 2000 and 2008. He finished among the league leaders in sacks and tackles for many of those seasons as well.

Despite his advancing age and the extremely physical, demanding nature of his position, Urlacher remained stunningly productive through the 2011 season. But a serious injury in January 2012 that damaged many ligaments in his left knee left his contract status with the Bears, and perhaps his future in the league, in jeopardy. The Bears let Urlacher, who has been the face of their franchise for more than 10 years, enter into the 2012 season without renegotiating his contract, which is in its final year. It’s probably a good business decision not to re-sign a 34-year-old linebacker, but will ultimately prove unpopular with fans.

After former Falcons quarterback Michael Vick was released from prison in 2009, the Eagles signed him to back up Donovan McNabb, breathing life into a career many thought was dead. McNabb, who seemed to be on tenuous ground in Philly since the day he was drafted, mentored Vick for one season before being replaced by him entirely in 2010.

Vick had a standout season for the Eagles in 2010 and and was rewarded with a six-year contract worth $100 million, despite missing four games with injuries. His health continued to be a problem in 2011 and so did his penchant for turnovers. This trend, and a concussion, saw the once-great QB lose his job to rookie Nick Foles.

After the 2008 and 2009 seasons, many were ready to give Red Sox designated hitter David Ortiz up for dead. His stats were down across the board in every statistical category except for strikeouts; not exactly something he was looking to increase. 

Celtics forward Kevin Garnett has long been one of the most talented, dominating and feared big men in the NBA. Talk of retirement has followed 36-year-old KG for years, but he’s defied his age and remained a productive player in Boston. In fact, in March 2012, when the Celtics were in serious need of a shake up, they asked Garnett to shift from forward to center, and the move paid dividends for Boston.

After years of statistical and physical decline, KG experienced a bit of a career renaissance in the second half of the 2011-12 season, helping lead the Celtics to a near upset of the Heat in a series nobody expected to go to seven games. That being said, there’s absolutely no question that Garnett’s golden days as the league’s premier power forward are well behind him.

What can be said about Yankees impotent slugger Alex Rodriguez that hasn’t already been said. The Yankees signed him to the richest, and worst, contract in the history of professional sports (at the time) in 2004; a 10-year deal worth $275 million. Which means for every game he rode the bench during the 2012 playoffs, he was paid a cool $169,753.09 to flirt with ladies in the stands and gnaw on sunflower seeds in the dugout.

Pretty sweet deal... for him. The Rodriguez contract was actually a pretty sweet deal for the Yankees too, until about 2008—at least during the regular season. A-Rod performed extremely well through the first few years of his contract and had the second-best season of his career in 2007 with 54 home runs, 156 RBIs, a batting average of .314 and he barely missed a game. 

Steelers safety Troy Polamalu was selected in the first round out of USC by the Steelers in the 2003 NFL Entry Draft. In order to get Polamalu, Pittsburgh did something they almost never do; they actually traded up from the 27th spot to the 16th spot in order to acquire him. Drafting is a hit-or-miss process in the league, but someone in the Steelers organization sure knew what they were doing that day. In a league largely devoid of true stud safeties, Polamalu alongside with the Ravens’ Ed Reed are two of the most dynamic playmakers at the position in NFL history.

Unfortunately, the wear and tear associated with his exceptionally physical style of play has taken its toll on Polamalu and he’s struggled with injuries in recent years, including concussion concerns made more serious by his history. Polamalu has remained a formidable force on the field, but he’s spent less and less time actually on it; having only played two full seasons since 2006. The injury he suffered in October 2012 had some asking if this most recent injury could bring the Polamalu era in Pittsburgh to an end in 2013.

Not everyone is going to agree that Heat superstar Dwyane Wade should be on this list; Heat superstar Dwyane Wade chief among them. There’s no question that Wade is still a top-tier talent in the NBA, but the argument can be made that he’s now the third-best player on his own team. He’s only two years older than Chris Bosh, but his health has become an ongoing concern and he missed 17 of 66 games during the lockout shortened season in 2011-12.

Spurs forward Tim Duncan seems ageless, doesn’t he? Well he has an age, and that age is 36. Duncan’s best days may be well behind him, but he’s remained a stunningly productive player in San Antonio throughout his entire career and has quietly had one of the greatest NBA careers of a generation. The argument can be made that Duncan’s career has even rivaled that of Lakers legend Kobe Bryant.

Ravens superstar safety Ed Reed, like the Steelers' Troy Polamalu, is approaching the end of a Hall of Fame career. Granted, in these waning years, his attitude toward the only franchise he’s ever played for has been a bit contentious.

Reed has been openly hostile toward Ravens quarterback Joe Flacco and it doesn’t seem that the NFL’s overall transition to a more offensive-minded game is sitting well with the defensive superstar. He’s been hinting at retirement nearly every season since 2008 and spent the entire 2012 offseason publicly stating that football was the least of his concerns, lest the Ravens give him the raise he was not so subtly hinting at.

In baseball, unlike football, players are rewarded for what they have done, not what they will do. How else would you explain the Phillies giving slugger Ryan Howard a five-year contract worth $125 million in 2010, with a sixth-year option that could keep him in Philadelphia until 2017.

Something tells me that given his performance since that big pay day, the Phillies aren’t going to be exercising his option in 2017. This is very common in MLB, so Howard’s big bloated contract (that he won’t even come close to earning) isn’t really the issue. The issue is that he peaked in 2006 with 58 home runs, 149 RBIs and a batting average of .312, but has been on a pretty steep downhill trajectory ever since. He followed up his career year with three more solid seasons, but has seen his production decline since 2010. His 2012 season was basically a lost cause after he tore his Achilles tendon in the final game of 2011 NLCS against St. Louis. He eventually returned to the field this past July, but was a shell of his former self, hitting just .219 with 14 home runs and 56 RBIs in 71 games.

Lakers legend Kobe Bryant probably won’t consider himself completely past his prime until he’s dead, but he did indicate in 2011 that he knows his basketball skills have diminished in recent years. Bryant's health has become a growing concern and he hasn't played a full season since 2010-11. His minutes and total points per game are both down from his peak year in 2005-06. That’s not to say that a Kobe Bryant a couple years past his prime still isn’t better than the vast majority of the NBA.

At age 34, many athletes are considered well beyond their expiration date, but Bryant, by most accounts, still ranks among the top 15 players in the NBA.

It’s not easy for a hockey fan to argue that legendary Devils goalie Martin Brodeur, one of the greatest goalkeepers of all time, is past his prime; but he is. What’s amazing is that the 40-year-old Brodeur is just a couple of years past his prime. He barely missed a game from 1995 through 2008, but in recent years it’s become increasingly clear that his age is finally starting to catch up with him. Brodeur has missed significant playing time over the last four seasons due to a number of injuries, leading many to wonder if it’s time for the future Hall of Famer to call it a career.

Anaheim Ducks right wing Teemu Selanne burst into the NHL as part of the Phoenix Coyotes during the 1992-93 season and instantly became a rookie scoring sensation. He netted 76 goals and 56 assists for a total of 132 points, an epic 387 shots on goal and shooting percentage of 19.6 percent.

Selanne had a career season in his rookie year, but remained a highly productive veteran, despite a few seasons hampered by injuries; up until the 2006-07 season. That's when the veteran Selanne, now 42-years-old, started a steady and steep decline in his production.

He experienced a surprise career resurgence in 2010-11 with 80 points, but it could very well be an outlier, and his best years are likely a decade behind him.

After nearly a decade of stellar play with the Rams, the team and running back Steven Jackson could very well go there separate ways next season. Both Jackson and the organization agreed to void the last year of his contract for the 2013 season, allowing him to test the waters of free agency or possibly retire.

Minus his rookie season in 2004 and his final season in 2008, Jackson has been one of the most dominating running backs of the decade. Over those seven years he averaged 1,203 yards per season, never once dropping below 1,000 total yards, 4.2 yards per carry, and was good for seven touchdowns a year. Jackson's career actually peaked in 2006, but the decline was exceptionally slow, showing no signs of real wear and tear until 2010 and 2011 when his attempts and yards per carry dropped in successive years.

Jackson's best days may be well behind him, but at 29 years old, there's still a chance he'll find a home in 2013 and remain productive for a few more seasons.

This one really goes without saying, doesn't it? If onetime global soccer superstar David Beckham wasn't years past his prime, he wouldn't be playing for Major League Soccer's L.A. Galaxy in the U.S. He’d be playing football overseas. In the past he's played for perennial powerhouses Manchester United and Real Madrid, but it's been six years since he left Spain for the states. During his time with the Galaxy, he did play two brief stints on loan to AC Milan, but the fact of the matter is that Beckham simply wasn’t good enough to play in a full-time role overseas anymore. In fact, after being one of the instrumental players in bringing the 2012 Olympics to London, he failed to even be named to their national team. And that speaks volumes.

Swiss tennis sensation Roger Federer stunned the tennis world in the summer of 2012 by winning his seventh Wimbledon title at the age of 30. It wasn't because he had never won that particular Grand Slam before, because he had. In fact, from 2003 through 2009 only one player not named Roger Federer had won.

Since first reaching the No. 1 ranking in 2004, Federer has won well over 20 Grand Slam titles and he's currently ranked No. 2 in the world at the age of 31. Which means that Federer's career certainly isn't over, but his prime is far behind him. Between 2003 and 2007 Federer was an unstoppable force on nearly every tennis court around the world, but the emergence of Rafael Nadal, Andy Murray, and above all, Novak Djokovic, has seriously challenged him for supremacy.

Jaromir Jagr, along with Hall of Famers Mario Lemieux and Ron Francis, led the Pittsburgh Penguins to consecutive Stanley Cup Championships in 1991 and 1992—helping the team achieve dynasty status in the NHL. Jagr and Lemieux were a feared, effective tandem, and Jagr’s trophy case underscores his greatness in the nineties. All told, he’s racked up five Art Ross trophies to go along with a Hart Memorial Trophy, and eight all-star selections. Not bad for a guy on a team with Mario Lemieux. At 40, Jagr is encountering the inevitable physical decline that comes with playing hockey from childhood and into middle age. However, his decline began well before Father Time came calling. When the Pens traded him to the Washington Capitals in 2001, it came amidst rumors about gambling and more than a little grumbling from the Czech himself. Jagr remained one of the greatest players in the game, but was never the same after leaving Pittsburgh. He’s only scored more than 30 goals once in the last decade; as a New York Ranger in 2006. As soon as he’s eligible for the Hall of Fame, Jagr will be a lock, but for now he’s a rental—bouncing between the KHL and NHL, and following up a single, lackluster season with Philadelphia by signing a one-year deal with Dallas.

by AMBER LEE (follow her @blamberr)