Running back Beanie Wells (left) congratulates fellow back Tim Hightower after a touchdown during a game last season.
 
 
The theory is this: A running back's body only has so many carries in it before it starts to break down.

Tim Hightower hears it, and shakes his head.

"Mentally, it's a self-fulfilling prophecy," Hightower said. "You hear something so much, you begin to believe it, whether it is true or not."

Coach Ken Whisenhunt uses multiple backs. That's a philosophy with which he arrived with from Pittsburgh, the notion that a stable of running backs give a team diverse weapons against an opponent. Maybe it could help a back like for instance, a young Beanie Wells, last a little longer in the NFL – "Let's face it, if you are getting 50 or 60 snaps as a running back in a game, you're going to wear down," Whisenhunt said – but it isn't the reason for working the depth chart.

It's about playing to each back's strengths, Whisenhunt said. Sometimes, it's about riding a "hot hand," as cliché as that might be.

It's also the reason whoever starts between Wells and Hightower is a virtual moot point.

Yet there is a reason teams worry about backs and their workload. Wells waves away the idea that age is a problem – easy for him to do given he doesn't turn 22 until Aug. 7 – noting the big year Thomas Jones had on the other side of 30 in 2009. It's about taking care of one's body, Wells said, a thought echoed by Hightower and fellow running back Jason Wright.

Hightower said the data he has seen says the average career for a running back has actually shrunk a bit than years past, even though running backs had more carries in those days with teams passing less and equipment less advanced.

"I think all that stuff (protecting backs) is overrated," Hightower said. "I think coaches just like two-back systems. I don't think it's about keeping guys fresher."

In many ways, there is a parallel with baseball's pitch counts, the concern of which have dramatically reduced the number of innings pitched by starting pitchers over the past 10 to 15 years. Some players with huge carry numbers one year – the record 416 by Kansas City's Larry Johnson in 2006, the 410 by Jamal Anderson of the Falcons in 1998 – have been followed by down years the next.

But the list of top carrying backs also has others (Tampa Bay's James Wilder, Eric Dickerson of the Rams) who followed up big-carry years with another good season, lending credence to Hightower's assertion that examples can be found to support both sides.

"You have to pay attention to the historical data but it depends a lot on the player," general manager Rod Graves said. "Given the way our guys work and our offseason program, I think they are able to carry more than the average running back."

Wells would like a chance to prove it. He has a team-best 176 rushing attempts as a rookie, well below what he had hoped. Some of that was the Cards' pass-first thought process, some was Hightower's presence.

"I want it. And I need it," Wells said of the ball. "Personally, I am not going to do great the first five to seven carries I get. I need time to get warmed up. It takes me time to get a feel for the game."

But Wells isn't naïve. "You know what needs to be done," he said. "You have to embrace and accept your role."

Hightower knows Whisenhunt will split up the time. That doesn't mean he won't get ready like he will receive 300 or even 400 carries.

"How do you prepare yourself for 10 carries (a game)?" Hightower asked rhetorically. "That's not my mentality and it will never be my mentality. You have to prepare yourself to be the guy, to put the team on your back. If you don't stay in that competitive mode, you won't be one of those top backs and you never will be."