Since Duce Staley started coaching the Eagles running backs in 2013, he has overseen different types of backfields. During his first two years, LeSean McCoy was clearly the lead rusher. In 2015, the Eagles didn't know if DeMarco Murray should be their top running back or a sideline observer. Last season, it was a committee led by Ryan Mathews and Darren Sproles.

Coach Doug Pederson wants a similar committee this season, although the personnel will be different with the additions of 250-pound bruiser LeGarrette Blount and 176-pound rookie Donnel Pumphrey. They'll join Sproles and Wendell Smallwood in a four-man backfield that will likely have Blount as its top rusher, but could take on a different form depending on the opponent.

"It may look to you guys each week like we're switching it up, but it's all predicated on the game plan," Staley said. "We want to get the big boy rolling, get him going. That's Blount. . . .You know how that train is. When a train gets full steam ahead, it's hard to stop. Then sprinkle everyone else around him."

Blount is bigger than any running back the Eagles have had in recent years, adding a physical presence to the team. Pederson and Staley agree that Blount could catch the ball if he needed - he has only 46 career catches - although that's role that will likely be filled by Sproles and Pumphrey.

Sproles logged a career-high 94 carries last season, but he expects that he could be used more as a receiver out of the backfield this season than as a lead rusher. Sproles wants 12-15 touches per game, which could come as a combination rushing, receiving, and returning. He turns 34 next week, but Staley is so convinced of Sproles' durability that he believes Sproles can still play 2-3 more seasons.

"Whatever Sproles is drinking, injecting, snorting - it was a joke, of course - we need to find it because that's the fountain of youth," Staley said. "This guy's 34 but he's playing like he's 26. He's running around out here on the practice field, he's beating veterans. . .he's staying after [practice], catching with the quarterbacks. He's doing extra work. Our days off, he's in the weight room. He's doing everything."

The Eagles hope that rubs off on Pumphrey, whose size drew comparisons to Sproles since his first day with the team. Pumphrey totaled more carries than any player in college football during the last four years, but he's been used mostly as a pass catcher this spring. That would seem to be the role the Eagles are priming him for in 2017 - and especially long-term, given Sproles' expiring clock. The Eagles' spin is they want to evaluate that part of Pumphrey's repertoire because he didn't catch the ball often at San Diego State.

"Don't get it twisted at all, we're definitely going to give him the ball in the backfield," Staley said. "We know he can do that. He handled [the catching] well. He went out there and surprised a few guys. I think our defense has a lot of respect for him already."

The concern with Pumphrey - at least outside the NovaCare Complex - is how he'll handle the physicality of the NFL at 176 pounds. Sproles and Brian Westbrook are examples of shorter running backs that thrived in Philadelphia, but both players carried more weight on their frames. So what will happen when Pumphrey gets hit?

"Can they hit him?" Staley said as a rebuttal. "I think there's two sides to that. He's slippery, he can make you miss, and he's fast - he can turn the corner. We all know his size, how big he is, how tall he is, but what I think you don't know is his heart."

Smallwood should not be the forgotten running back. He rushed for 312 yards and 4.1 yards per carry as a rookie before missing the final three games because of a knee injury. The 2016 fifth-round pick is only 23 after leaving West Virginia following his junior season, and he'll fit in the team's rotation again this season.

The coaching staff is impressed with his progress entering his second season. Staley said most people might expect a player makes a "leap" from Year 1 to Year 2, but Staley looks for a "jump." He's seen that from Smallwood.

"Over the OTAs, I believe Wendell has been the most improved," Staley said. "He's been out there [and] you can see how he's now a little more comfortable in the passing game, a little more comfortable in protections, a little more comfortable in the run game. So we're throwing a lot at him and he's eating it up."

Staley took that leap when he played in Philadelphia, rushing for 1,000 yards in 1998, his second of seven seasons playing for the Eagles. He joined the coaching staff as an intern in 2010 and has been an assistant since 2011. This will be his seventh season, meaning his coaching career in Philadelphia has lasted just as long as his playing career.

He finds himself shaking his knee when one of his players takes a cut, mimicking the motion he made as a player. But Staley is now a tenured coach, far beyond his playing career, and working his way up the coaching ladder. He interviewed for the Eagles' head coaching job last year and he called plays at the East-West Shrine Game. Becoming a play-caller may be the next step in his trajectory - one that he hopes includes being a head coach.

"No doubt about that," Staley said about whether he's ready to call plays. "I truly believe that. It's all about studying, being comfortable in that role, being able to call plays and know your personnel. That'll be a fun part of it. Hopefully, that's down the road. But right now, I'm focused on this role."