By Dan Durkin-

(CBS) In a league dominated by three-wide (or “11”) personnel, the 49ers are a relic. They are a conventional, two-back offense that runs power football more effectively than any team in the league.

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That’s not to say the 49ers deploy a simple scheme. Far from it. Throughout the course of a game, they will use power, counter, lead, veer and zone read plays 30-plus times, so their focus becomes how can they make it appear different to their opponent.

Their complexity comes from formations, motion, shifts and unbalanced lines that are deployed using a multitude of personnel groupings. All it takes is a single defender to be unsound in his run fit to create an explosive play.

Blending a mobile quarterback like Colin Kaepernick with coaches rooted in a physical brand of football — head coach Jim Harbaugh and offensive coordinator Greg Roman — was a perfect match. Kaepernick brought the pistol offense to the NFL and runs it with tremendous effectiveness, but San Francisco’s base concept remains the power running game.

“That’s a team that everybody looks at, ‘Oh, with Kaepernick, they run all this pistol read option and option stuff,'” Bears defensive end Jared Allen said. “They are going to line up, and they will run the power down your throat. So it is still a conventional team.”

The 49ers do just that, and the wrinkle they throw in to take advantage of Kaepernick’s mobility is running bootlegs off of their power game when teams start crashing hard on the backside.

Let’s go to the film room to take a closer look.

(All images are courtesy of NFL Game Rewind. Click to enlarge them.)

The first example comes from the 49ers’ Week 1 matchup against the Cowboys. The 49ers come out in 11 personnel in a doubles formation and run power to the strong side (right) of the formation.

On the frontside, the 49ers down block with tight end Vernon Davis and right guard Joe Looney (yellow lines), and pull right tackle Anthony Davis and center Daniel Kilgore (red lines). On the backside, left guard Mike Iupati flows to the second level to block the middle linebacker (black line) and left tackle Joe Staley (white line) cuts the three technique.

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Kilgore is able to seal the linebacker, and Davis has his eyes inside to clean up any trash that makes it through, creating an alley for Gore to press, while wide receiver Steve Johnson obstructs the safety.

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Gore keeps his pads low with a good leg churn en route to a 12-yard gain.

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There’s nothing fancy about this play. It’s simple power football that results in an explosive run (defined as 12 or more yards) and moves the chains.

Let’s now take a look at an example of a weak bootleg off of a power run from the NFC Championship game against the Seahawks last season.

The 49ers come out in 12 personnel in a unit wing formation showing a power run to the strong side of the formation. Left guard Adam Snyder pulls to sell the run action as Gore executes the play fake and presses the hole.

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Notice how hard Seahawks’ weak-side linebacker Bruce Irvin (circled in white) crashes down from the backside on the power run action, leaving Kaepernick with plenty of room to run on the bootleg keeper to the weak side, picking up 22 yards.

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This is just one example of the variations the 49ers have built in to their base running game, all of which are designed to create conflict and put extra stress on a defense to be assignment sound. With a talented runner like Kaepernick, the 49ers essentially double their playbook using simple misdirections and orchestrated line play.

Compared to Bills quarterback EJ Manuel, Kaepernick is a decidedly better athlete, so the Bears will face a more sophisticated scheme this weekend operated by a more dynamic signal-caller. The key to slowing is making sure every player on the defense doesn’t try to do too much against a player like Kaepernick, Allen said.

“Sometimes the best thing to do is when you’re backside, you have to remain backside,” Allen said. “That just comes down to trust. You’ve got to be in your gaps.”

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Dan Durkin covers the Bears for CBSChicago.com and is a frequent contributor to 670 The Score. Follow him on Twitter at @djdurkin.