CINCINNATI -- Hue Jackson was encouraged by the work his running backs showcased near the end of the 2014 season, but the Cincinnati Bengals offensive coordinator is convinced the unit has barely scratched the surface of what it can do overall.

"I was happy we ended the season running the ball the way we did but there is still so much more there," Jackson at last week's NFL combine. "We left a lot of meat on the bone."

While many outside the locker room praised rookie Jeremy Hill's play -- particularly during the final nine weeks of the regular season when he led the league in rushing -- Jackson was letting Hill and fellow back Giovani Bernard have it.

Their harshest critic, Jackson made no qualms about wanting to see them break even more tackles, slip more defenders and get even bigger gains. He was only so critical because he still believes the two running backs can be the bedrock of his offense.

In 2013, Bernard was an outside candidate for the NFL's rookie of the year award. Hill was in the mix this past season. Neither won, but the recognition they received was a testament to how well they fit in the Bengals' multiback scheme that's designed for the load to be shared. Unlike other teams, Cincinnati doesn't want to be paced by a single back. Jackson believes a player wears down faster if he is the only running and passing option out of the backfield.

When it came to catching passes out the backfield, the first-year Bengals coordinator was truly impressed.

His running backs combined for 80 receptions last season. That's more than the position group had during any other year in this four-season playoff run. The running backs had 60 receptions in 2013, 43 in 2012 and 53 in 2011, the year the Bengals began this stretch of postseason appearances. The team still, of course, hasn't won a playoff game since 1991.

Bernard did the heavy lifting in the passing game in 2013, catching 56 passes to the four that BenJarvus Green-Ellis had. There was a more even split this past year. While Bernard caught 43 passes, Hill caught 27. Backups Rex Burkhead and Cedric Peerman combined for the other 10.

"People keep saying, 'Well, Gio didn't catch a lot of balls,'" Jackson said. "Well, that's because we had another guy who could catch the ball very well. That gives us another threat. That position caught 80 balls last year. That is quite a bit for a running back position."

It is, but consider this.

Two running backs, Chicago's Matt Forte and Pittsburgh's Le'Veon Bell, had more than 80 receptions this season by themselves. There also were eight other teams that had two or more running backs who caught 25 or more passes each. Only two of them, however, the Lions and Colts, made it to the playoffs with the Bengals.

As encouraged as he was about his running backs' receiving numbers, Jackson still isn't convinced Hill has done his best job helping quarterback Andy Dalton have time to pass to other players.

"You earn the right [to play] by pass protection," Jackson said, adding that injuries to Bernard helped accelerate Hill's playing time. "It wasn't his running ability. That's [pass protection] what we drafted him for. He would be the first to tell you we need to grow in that area."

Growth is precisely what Jackson is predicting for Hill and Bernard in 2015.

"There is more in there for both of them," he said.