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In the days leading up to Training Camp, we will take a look at the most pressing questions facing each position group. Today, we look at perhaps the most loaded position on the roster, running back ...*

1. Will DeMarco Murray Hold Up?

Despite the silly recent comments by the likes of Joseph Randle and Emmitt Smith, DeMarco Murray's 2014 season is beyond reproach. In leading the league with 1,845 rushing yards, 13 rushing touchdowns and 2,261 yards from scrimmage, Murray was the league's best back. Whether or not he "left some meat on the bone" is a ridiculous argument, as if Aaron Rodgers should be reprimanded for every incompletion or J.J. Watt should be criticized for the handful of missed tackles he had last season.

The issue at hand, however, is projecting Murray's future in a league where the shelf life of an elite running back can often be so short. In leading the league with 392 carries last season, Murray took on a workload that puts him in rare company – company which has not typically worked out well in the past. The admittedly arbitrary cutoff of 380 carries in a season has been hit 17 times, with Hall of Famers like Walter Payton and Eric Dickerson among the group. Of those 17, Dickerson and Payton are the only two whose yards per carry increased the following season (Dickerson did it twice in fact). They're Hall of Famers for a reason.

If we limit the scope to only the last 20 years, the 380-carry mark has been hit nine times. Of the eight who preceded Murray, only two even played more than eight games the following season, while only one played in all 16 games.

*Williams did not play football in 2004.

The good news is that this information is nothing groundbreaking and is something with which Chip Kelly is certainly familiar. And Kelly is not without a plan. First, Murray will not be counted on to carry the full load for the Eagles like he did in Dallas, where he accounted for 77 percent of the team's total carries, outpacing the second-leading rusher, Randle, by 341 carries. The presence of Ryan Mathews, himself a two-time 1,000-yard rusher, and Darren Sproles should mitigate the workload placed on Murray.

Second, the Eagles' organizational emphasis on player health and the mysterious sports science will be leaned on to help Murray stay spry.

"I feel stronger than I've ever felt and I feel faster than I've ever felt, and hopefully it's going to be a good year for us," Murray said in the spring, a sentiment he repeated later to Rich Eisen. 

If Murray remains healthy, there is little doubt that his running style is a perfect fit for the Eagles offense, and the Eagles offensive line is eager to prove that they can one-up their rivals in Texas. With all due respect to Sam Bradford, following Muray's success in 2015 may be the season's most intriguing storyline.

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2. How Often Will Kelly Call On Mathews?**

Of course, this question ties in with the one above, but Mathews should not be overlooked as some second-tier option. Mathews has two 1,000-yard seasons on his docket, proving his effectiveness. Unlike Murray, over whom we're debating the potential risk of injury, Mathews does have a history of missing time. In fact, his two 1,000-yard seasons, in 2011 and 2013, are the only two of his five seasons in which he's started more than 10 games. He played in only six games last year, rushing for 330 yards on 4.5 yards a carry.

The flip side to that injury history is that, despite being in the league for one more season than Murray, Mathews actually has less tread on his proverbial tires, with 923 career carries to Murray's 934. Mathews has also been an effective receiver at times in his career, though, perhaps because of changes in the Chargers offense, that role diminished as he went from a career-high 50 catches in his Pro Bowl 2011 season to 39 in '12, 26 in '13 and only nine last year.

Last year, LeSean McCoy accounted for 312 of the team's 474 carries on the season, or just fewer than 66 percent. Darren Sproles finished second on the team with 57 carries and Chris Polk came next with 46. Among the three top running backs, then, the split on carries went 75 percent to McCoy, 14 percent to Sproles and 11 percent to Polk. Sproles' role on the ground is a question for another question down below, but it's hard not to envision Kelly opting to creep those percentages closer to something like 55-60 percent for Murray, 25-30 percent for Mathews and the remaining touches for Sproles. Kelly and running backs coach Duce Staley have surely spent some time laying their best plans for how this rotation might work.

3. So Where Does That Leave Darren Sproles?

Sproles was such a revelation for the Eagles last season, when he burst onto the scene with big-time plays both on offense and special teams. Where he did not make quite the impact some had expected was as a receiver, where he notched 40 catches (still fifth on the team), his fewest in six seasons. Perhaps the addition of Mathews and Murray allows Sproles to be deployed in different ways, or perhaps Kelly will keep Sproles ready to unleash as a change-up for opponents.

There's little need to dig further, though, because this is such an interesting question that it's already been discussed in our Big Question.