[+] Enlarge Al Messerschmidt/Getty Images How long can Jurgen Klinsmann depend on the likes of Steve Cherundolo, who'll be 35 in Brazil? "I'm not age-related, I'm performance-related," says the manager.

CARSON, Calif. -- For the U.S. men's national team, no area of the field has been scrutinized this World Cup cycle quite like the back line. Some longtime contributors are getting up there in years, and while Timothy Chandler has emerged as part of the solution at left back, other candidates have been slower to emerge, adding a fair amount of uncertainty to manager Jurgen Klinsmann's long-term plans.

For that reason, the defenders called in by Klinsmann for this year's January camp in Southern California are being looked at closely to see whether one or more of them might move up the depth chart. Some performers who got looks during the last World Cup cycle, including Michael Parkhurst and Heath Pearce, have been called in, as have some players with less national team experience such as Geoff Cameron, A.J. DeLaGarza, Jeff Parke and Zach Loyd.

"We build basically what is the next line underneath, and another line underneath that," Klinsmann said. "For each position we are trying to build competition. These guys, they are highly competitive, they want to show what they have. They have done a tremendous job so far. They are hungry, they want to challenge for those spots. And by the end of the camp, with two games that we can see and evaluate, we know where they would fit in this whole picture, this whole depth chart basically."

Moving into the front of Klinsmann's consciousness will take some doing, however. The German indicated that for the present, he is perfectly content to stick with a back four of Chandler, Oguchi Onyewu, Carlos Bocanegra and Steve Cherundolo. The only problem is that Bocanegra and Cherundolo will be 35 years old when the 2014 World Cup rolls around, raising concerns that the U.S. will be relying on two players well past their primes. Yet Klinsmann insisted that he wouldn't be averse to seeing them taking the field in two years.

"I'm not age-related, I'm performance-related," Klinsmann said. "We look at every game with their clubs, we look at every game they play with us, we look at every training session. If we get the feeling that a certain position is losing it a little bit, then the next guy is there to bite their ears off. And if there is a younger one that is taking over, then he will take over.

"But you have sometimes specific positions with experience that keep the whole team together, that keep the whole chemistry together. They do so much on the field that you say, 'You know what? For these reasons the younger player has to wait a little bit more because [the other player] is too valuable for the group.'"

“ If we get the feeling that a certain position is losing it a little bit, then the next guy is there to bite their ears off. And if there is a younger one that is taking over, then he will take over. ” -- U.S. manager Jurgen Klinsmann

For those assembled in California, the odds of breaking through are even longer given that some additional candidates are missing the camp because of club commitments or injury. Tim Ream, pending approval of his work permit, is set to join EPL side Bolton Wanderers. George John has joined English second-tier side West Ham United on a short-term loan with the club having an option to buy. Reigning MLS Defender of the Year Omar Gonzalez had surgery to repair a torn ACL. Clarence Goodson, the primary backup to Onyewu and Bocanegra, is also absent.

All the more reason for the players at camp to make the most of their opportunities. "The World Cup is in two-and-a-half years, so you want to make a name for yourself right now, these three weeks you have with Jurgen and the other coaches," DeLaGarza said. "It's a good opportunity for the guys to put their name in his head for the next games to come and qualifying."

Of those assembled, it would appear that Cameron and Parkhurst have the best chances of making an impression, especially given their skill on the ball and ability to play multiple positions. The two got off to a good start in Friday's scrimmage against the U.S. under-23 national team. The prospective Olympians were on the front foot initially and in the first 15 minutes carried the game to the senior team. But with Cameron dominating in the air and Parkhurst using his savvy positioning on the ground, the national team was able to absorb the pressure and eventually found its feet on its way to a 4-0 win.

The pairing of Cameron and Parkhurst marked a reunion of sorts in that the two played youth soccer together with Bayside FC in Rhode Island. But more importantly, the duo managed to overcome the impulse of playing just to impress the coaches and instead focused on helping their teammates perform as well.

"There's a little bit of a conflict in terms of approach, but my view has changed a little bit regarding camps like this," Parkhurst said. "I used to be stressed about it and worry about making an impact, but it's tough to play that way. Now I look at it more as an opportunity rather than pressure. I just go out there and try to have fun and do the things that I'm good at. If that's good enough, then I'll get another shot down the line, but if it's not then it's not meant to be, so I'm not trying to put more pressure on myself."

[+] Enlarge Jeff Golden/Getty Images "The World Cup is in two-and-a-half years, so you want to make a name for yourself right now," said the Galaxy's A.J. DeLaGarza.

Of course, the real test will come Saturday when the U.S. faces Venezuela in Glendale, Ariz., then travels to Panama to play the Canaleros four days later. But so far, Klinsmann has liked what he has seen. He added that in addition to Cameron and Parkhurst, he was pleased with the willingness of Pearce and Loyd to keep the ball on the ground.

"They got the clear message," Klinsmann said of his defenders. "We don't want them to hit long balls unless there is no space or no opportunity. If you look at the reality, the long ball is 80 percent gone. I don't want 80 percent gone. I want to try and find ways to solve it, and keep it and then move forward. So we emphasize that and we tell them that, and they adapt to it. If you give them a challenge, they adapt to it, and you go from there.

"It's really a good process. It's a short one, that's the only problem. What is it? Twelve days [so far], and in six days we hit an international game. That's very tricky. But in those 12 days we saw already a lot of good stuff from them, and their willingness and eagerness to make the next step and get feedback from us is really cool to see."

If one of these players can eventually challenge for a starting spot, that will be even cooler for Klinsmann & Co.

Notes:

• The now annual January camp is often referred to as Camp Cupcake, although that is typically done with tongue firmly planted in cheek, since gaining fitness has long been one of the primary goals of the get-together. But this year the moniker is even less apt. The day starts with an early-morning run of about 30 minutes followed by a morning practice session and another in late afternoon. There are also plenty of meetings and activities between sessions.

"It's been a grind, but a good grind," Parkhurst said. "We all need to get our fitness levels higher so it's a little bit easier now that we're in Los Angeles. The first week in Phoenix was rough. I think most of us are exhausted by 9:30 p.m. I struggle to stay awake until 10."

• The national team will scrimmage the U-23 team once more Tuesday before heading out to Arizona for the game against Venezuela.

• Forward Juan Agudelo suffered a right ankle sprain during Friday's scrimmage. He will be re-evaluated Monday to determine his status.

• Cameron confirmed after Friday's scrimmage that he is feeling no ill effects from the knee injury he sustained in November's MLS Cup final. Shortly after returning to Houston, he underwent a plasma injection to speed the healing process, and he is close to 100 percent.

"I felt [the knee] the first couple of days when we were training," he said. "I felt some of the scar tissue, but now it's pretty much gone. I feel it here and there, but it's getting close to where I'm not feeling it at all at practice."

• Parkhurst said that after more than three years with Danish side FC Nordsjaelland and with his contract due to expire at the end of 2012, he'll be looking to move on after the current season.

"Obviously if it's in the summer I'd like to stay in Europe and explore those options," he said. "But at the same time, I don't want to be over in Europe for another five, six years. MLS is definitely something that I'll come back to, whether that's a year from now, or in a couple of years, I don't know."

Parkhurst confirmed that his former club, the New England Revolution, still owns his MLS rights.

Jeff Carlisle covers MLS and the U.S. national team for ESPN.com. He is also the author of "Soccer's Most Wanted II: The Top 10 Book of More Glorious Goals, Superb Saves and Fantastic Free-Kicks." He can be reached at eljefe1@yahoo.com.