Sims said he has gained 15 pounds this offseason, hoping to increase his power after weighing less than 300 the past two years with mixed results against bigger players such as Minnesota's 311-pound defensive tackle Kevin Williams.
"I wouldn't do it if I didn't see that there was a problem," Sims said Thursday. "This is something I think is going to make me better, which will make this team better."
Sims has started every game for the Lions since they acquired him and a seventh-round pick in a 2010 trade with Seattle for defensive end Robert Henderson and a fifth-round selection. He started 34 of 45 games in his four seasons with the Seahawks after they drafted him in 2006 out of Ohio State in the fourth round.
Sims, who is under contract in Detroit for three more years, has stopped a revolving door for the franchise at left guard with solid play the past two seasons. He has been analyzing his game and body since helping the Lions reach the playoffs last year for the first time since the 1999 season.
The native of Macedonia, Ohio, figured out why he struggled to keep weight on the past two years when he ate burgers on the drive to work just to tip the scales at more than 300 pounds.
"This is the hardest I've ever worked," he said. "I wasn't ready to be honest. The stuff they demand of you here and how we practice. It's an old-school mentality. I couldn't keep it where I was in Seattle. Coach (Jim) Schwartz demands a lot of you."
Sims and assistant coaches have been watching him play on film to come up with ways to help him improve how he blocks on runs and on screens in particular.
"They're like, `You're a good guard in this league. How do we get you to be a great one?"' he said. "It's small things we need to change."
"Gos and Jeff are doing what they need to do and not worried about that," Sims said. "Just like I don't think Riley is worried about starting right now. We're just going to go to work."
The first-round pick, though, was drafted to be a first-string player at some point by a team without much young talent on the offensive line.
"There's always going to be chatter when a guy like that comes in your room," Sims acknowledged. "You've got some guys that are going to struggle with it because let's be honest, a guy like that comes in and somebody is going to be looking for a job eventually."
When Sims' career is over, he plans to drastically reshape his body to get well below 300 pounds in part because his father, former Cleveland Browns defensive tackle Mickey Sims, died of heart disease at 51.
"There's no reason to be this heavy other than to play football," he said.
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