LOS ANGELES - The back problems that bugged John David Booty for years are finally behind him.

That being the case, the Southern California quarterback was able to participate in a rigorous training program administered by strength and conditioning coach Chris Carlisle this summer.

The results are obvious.

“I think the offseason program made a big difference,” Booty said. “The SC program, you see guys year after year looking like NFL players.”

Booty, a fifth-year senior, finally got his shot at playing last season after sitting and watching Matt Leinart star at quarterback for three years. He made the most of it, passing for 3,347 yards and 29 touchdowns with nine interceptions.

For a while, it appeared Booty might not get his shot. He underwent back surgery in March 2006 after experiencing problems since his junior year in high school because of a herniated disc, and had to beat out freshman Mark Sanchez for the starting job last summer although he still wasn’t in tiptop condition.

He is now.

“For the first time since his sophomore or junior year in high school, John David felt comfortable, and it opened up his ability to train the way we’ve trained quarterbacks here before,” Carlisle said. “We did a lot of core work — abdominal, lower-back work.

“He has more zip on the ball as a result because he has more power coming from the core and his legs. His body weight went up to 220 (pounds). He stands in the pocket now and knows he can take a shot without worrying about it. He’s pain-free and confident in what he can do.”

Trojans coach Pete Carroll has noticed a big difference.

“The fact that he can just work out regularly with coach Carlisle in the program where he couldn’t do that a year ago makes all the difference in the world in his confidence and athleticism,” Carroll said. “John David has had an incredible run since the springtime.”

Offensive coordinator Steve Sarkisian said Booty reminds him of four-time Cy Young Award winner Greg Maddux because of his accuracy.

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“I think the thing that jumps out at you is his ability to fit the ball in tight quarters,” Sarkisian said. “You ever watch Greg Maddux? He doesn’t miss.”

Sarkisian believes Booty took a giant step in the Rose Bowl game last New Year’s Day, when he passed for 391 yards and four touchdowns in a 32-18 victory over Michigan.

The game was tied 3-3 at halftime, and that’s when the decision was made to turn to the passing game, with Booty throwing the ball 27 times in 29 plays.

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“I think the great thing you saw about him that day, he just went out and played football,” Sarkisian said. “I think that was a great catapult for this season. He could just go out and play free. The great ones do that kind of stuff.”

Sarkisian has also worked with Heisman Trophy-winning quarterbacks Leinart and Carson Palmer, who are both starters in the NFL. He believes Booty has that kind of ability.

“I think he’s going to be fantastic — he’s a great prospect,” Sarkisian said.

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Booty was recently elected as a team co-captain for the second straight year, meaning his teammates had that kind of respect for him before he ever started a game.

“That’s a testament to his impact on the team,” said third-string quarterback Michael McDonald, another fifth-year senior. “We all had faith in him.”

Booty said he felt it was his responsibility to spend this summer in Los Angeles rather than with his family in Shreveport, La.

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“Being a captain, I really felt it was a duty to be here,” he said.

And being here caused him to miss the wedding of Jacob Hester, a longtime friend who happens to play fullback for LSU.

“I really hated to miss it. We had workouts that Friday,” Booty said. “He understood. We talked, even the day of.”

Booty and Hester would love to have a reunion in New Orleans next January. That’s the site of the BCS championship game, and No. 1 USC and No. 2 LSU are preseason picks to get there.

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“I really don’t think about that stuff right now,” Booty said. “We haven’t won any games yet. That would be great, but guys who start worrying about that, that’s how you get beat.”

Booty is considered a contender for the Heisman Trophy, but said he’s not thinking about that, either.

“I think it takes care of itself,” he said. “If you play well at this university, you have a shot at it. Whatever’s going to happen is going to happen. I feel fortunate to be on the list with these great players. To be mentioned with them is really an honor at this point.”