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The Arizona Cardinals had arguably the NFL's best offense during the 2015 season. They got there through a combination of explosiveness and efficiency that was nearly unmatched. The Cards led the NFL in total yards and finished a mere 11 points behind the Carolina Panthers for the league lead. They paced the NFL in yards per play and finished a very close second in both yards per drive and points per drive.

Most of that performance was driven by their passing offense. The Cardinals finished the season second in passing yards, first in yards per attempt, tied for third in passing touchdowns, and third in Football Outsiders' pass offense DVOA (Defense-adjusted Value Over Average, which adjusts performance for down, distance, and opponent). Despite the fact that the Cardinals threw a pass on only 54 percent of their offensive plays (not including sacks), they gained 70.7 percent of their yards through the air. That gave them the league's third-largest disparity between percentage of pass play and percentage of total yards via the pass.

What does that mean? Well, it mostly means that the Cardinals' run game was good, but not quite elite. Arizona finished the 2015 season with the eighth-most rushing yards and sixth-most rushing touchdowns, but ranked just 12th in yards per carry and 16th in rush offense DVOA. Arizona's three-headed running back monster -- Chris Johnson, Andre Ellington, and rookie David Johnson -- was only active for eight of the team's 16 games, though. Ellington missed Weeks 2-4 and 13-15 with injuries, while Chris Johnson's season ended after Week 12 thanks to a fractured tibia.

All three of those players led the team in touches for at least one game, with Chris Johnson leading 10 times, David Johnson leading five times (the final five games of the year), and Ellington leading once (Week 1).

CARDINALS RB TOUCHES (WEEKLY LEADER IN BOLD)
WEEK C. JOHNSON ELLINGTON D. JOHNSON
1 10 13 1
2 20 --- 6
3 23 --- 10
4 19 --- 7
5 11 3 3
6 15 3 4
7 18 8 5
8 30 3 3
10 25 8 1
11 19 3 4
12 12 8 10
13 --- --- 24
14 --- --- 24
15 --- --- 33
16 --- 8 12
17 --- 3 14
ALL 202 60 161

With the exception of Weeks 1, 7, and 12, whichever back led the team in touches during a particular week also received at least 60 percent of the touches in that game. There was rarely an even distribution -- the only time each of the three backs received at least a quarter of the touches was Week 12, and that was the week Chris Johnson got injured.

With all three players returning for the 2016 season, head coach Bruce Arians has his work cut out for him figuring out how to distribute the touches between them. "It's my job to get them the ball enough because they can all do different things," Arians said, per ESPN.com.

How will they be distributed? We already have a pretty good idea. "David's earned the right now to be the bell cow," Arians said. "Everybody's got to take it from him. But Chris ran for 800 (yards) and probably would have had 1,200 had he stayed healthy. Andre can break the game open."

So David Johnson has the first shot at being the "bell cow." What exactly does that mean? Based on last year's distribution, the lead back in a given game received approximately 66.3 percent of the touches. Assuming last year's total of 470 touches (the 423 accumulated by this trio, plus the 47 touches given to Kerwynn Williams and Stepfan Taylor) holds steady, that would mean 311 touches for David Johnson and 159 to be split between Chris Johnson and Ellington (provided all three players are active for all 16 games).

That distribution includes games where only one or two of the backs was healthy in a given week, though. What about the the eight games where all three players were healthy? Well, there actually was not much of a difference. In those eight games, the lead back received approximately 65 percent of the touches. That would mean 305 touches for David Johnson and 165 to be split between Chris Johnson and Ellington.

That's a huge workload. Only four backs (Adrian Peterson, Devonta Freeman, Doug Martin, and Latavius Murray) reached the 300-plus touch mark last season, though an average of 7.2 backs per year have done so over the last five seasons. It might not be a coincidence that only nine backs have multiple seasons with 300-plus touches in that time, or that of the 13 with just one such season, six are basically out of football, while three more are already severely diminished players from their peak.

A more equitable distribution that would keep all three players healthy and upright not just this season, but over the long term, might see David Johnson get somewhere around 55 percent of the touches, around 260 of them. That would leave 210 touches for Chris Johnson and Ellington to split. That'd mean just over 16 touches a game for David Johnson and just over 13 a game between Chris Johnson and Ellington. While that may not seem like a whole lot of usage for Chris Johnson and Ellington, there are other factors to consider.

First, David Johnson is the youngest of the group by three years, and has by far the least amount of tread on his tires. Second, he's by far the biggest player of the group at 6-foot-1 and 224 pounds. Ellington is listed at 5-10, 199 and Chris Johnson is listed 5-11, 195.

Not only that, but Chris Johnson was the least efficient of the trio last year, averaging 4.32 yards per touch to David's 6.45 and Ellington's 7.28. He's the oldest of the three by four years, so that's not much of a surprise. He'll also be 31 years old this coming season, and seven years removed from the last time he averaged at least 5.0 yards per touch. It wouldn't be surprising at all if he couldn't produce in a similar manner to last year.

Meanwhile, Ellington was a yards-per-touch maestro as a rookie, but he broke down as the Cardinals handed him a bigger workload in 2014 (dropping from 6.52 to 4.27 yards per touch as he went from 10.5 to 20.6 touches per game). He became more efficient again with a slighter workload (6.0 touches per game) in 2015, so it makes sense to keep him at around 8-10 touches per week so that he doesn't either break down or lose his explosion.

Of course, the numbers probably won't work out exactly this way. It's a near guarantee that at least one of the three will miss a game here or there, and Arians will ride the hot hand a few times as well. In the end, having three very capable running backs is a good "problem" to have. Depth is important, especially as positions where players often get bumps and bruises. Whether Arians can keep all three players happy with their amount of touches is another story, but if the Cardinals win as often as they did in 2015, things will probably be alright.

Arizona's running back trio will all return in 2016. (USATSI)