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Jim Harbaugh likes the fact that 49ers quarterback Colin Kaepernick works hard in the offseason. But he’s a little worried that Kaepernick could be overdoing it.

In fact, Kaepernick works so hard in the weight room that Harbaugh is worried his upper body could be getting so big and muscular that it could affect his throwing motion.

“If you’re just talking about weightlifting and upper-body strength, yes, I think there is that fear,” Harbaugh told Matt Maiocco of CSNBayArea.com. “It’s something we’ve talked about. ‘I don’t want you getting too jacked-up, Colin.’ I want some speed, quickness.”

Although in past years some Super Bowl losing teams have seemed to have a Super Bowl hangover afterward, Harbaugh said that with his team, the only thing he notices is that players want to hit the weight room harder than ever.

“I never had to concern myself with that because the players we have, the coaches we have. They’re already back in the building,” Harbaugh said. “Justin Smith is already, arm in a sling, champing at the bit to get back. Colin Kaepernick is already working out, pulling chains. So it’s not a challenge for me.”

The challenge might just be getting Kaepernick not to go at it too hard.