PITTSBURGH — When the Pittsburgh Steelers asked David Johnson to convert from tight end to fullback full-time in time for the 2012 season, the burly 270-pound Johnson’s first thought was “I need to go on a diet.”

A couple months and 20 pounds later, Johnson is embracing a move that could extend the former seventh-round pick’s NFL career indefinitely.

To be honest, the decision came as a bit of relief for Johnson. He spent last season meeting and practicing with the tight ends all week only to be thrown into the backfield as a lead blocker in goal line situations with little preparation.

“Last year, he was just trying to hit it on the fly,” tight end Heath Miller said.

Now Johnson — who will keep the No. 85 — sits in meetings trying to absorb as much of new offensive coordinator Todd Haley’s playbook as he can while getting a feel for what his role will look like when the season starts in September.

“It’s actually a little bit easier,” Johnson said. “That’s all I’ve got to learn now is fullback. At first I had to know both tight end positions and fullback. Now I just focus on fullback and just create my better habits on that and become the best at it.”

The position, once a mainstay, has been phased out by most teams in favor of three-receiver sets even in Pittsburgh. The spot has been vacant since Dan Kreider left the team following the 2007 season as former offensive coordinator Bruce Arians opted for a more pass-heavy attack.

While Haley still plans to let quarterback Ben Roethlisberger do his thing, he also wants to give Pittsburgh’s running game a physical presence it has lacked at times since Jerome Bettis’ retirement following the 2005 season.