Fueled by a fierce determination to succeed and an unrelenting work ethic, Sam Mustipher transformed himself last season from an undrafted practice squad player into the Bears' starting center.

"Pretty cool story," said coach Matt Nagy. "Last year, the chance he had to get in there and play, he took advantage of it. How do you not like a success story like that of a guy that was not drafted to be able to come in here and do that?"

After spending his first season-and-a-half with the Bears on the practice squad, Mustipher became the starting center midway through the 2020 campaign and helped key an offensive resurgence led by a revamped line.

His emergence was impressive, but the Notre Dame product remains just as motivated to excel as he was when he was battling for a roster spot. That was evident during the offseason when Mustipher added 10 pounds of lean muscle mass.

The extra weight will help the Bears center contend with the behemoth defensive linemen that he's entrusted with moving off the ball. Mustipher bulked up by spending more time in the weight room—and at the dinner table.

"I ate whatever I wanted to; it was an offensive lineman's dream," Mustipher said. "And just trying to get as strong as possible.

"Working out hard, honestly, and eating, that's really the biggest thing to it. There were some weeks where I was doing 10-plus workouts in one week, just trying to get strong, trying to get faster. I think my official weigh-in was 332, and I came back even heavier than that for OTAs … It was just dieting the proper way, cutting out carbs at night, drinking enough protein, getting all the grams in."

Mustipher achieved his goal to get bigger and stronger, not bigger and softer.

"I don't think it's as much the weight as it is muscle," Mustipher said. "I think I'm at the highest amount of lean body mass I've ever had in my life, which was huge. That's something I worked with [Bears sports science coordinator and dietician] Jenn Gibson on to figure out what do I need to do this offseason: 'How do I need to train? What are the foods that I need to be putting into my body for me to reach those goals?'

"My strength numbers went up. That was the critical thing. You can get big and just get fat and slow. I wanted to get strong and explosive. And so, I feel like that's where I put the weight on."

For the second straight offseason, Mustipher trained with former Bears center Olin Kreutz, a six-time Pro Bowler in 13 seasons in Chicago from 1998-2010. The tough-as-nails Hawaii native seemingly hasn't changed much from his playing days when he was a highly respected leader who demanded a lot from himself and his teammates.

"You've got a guy who played that long at that high of a level," Mustipher said. "You come into the gym and you've got to understand that you've got to match a certain intensity. It doesn't matter how you feel—if you're sore or if you're tired—you've got to match that intensity every day. And the way he approaches everything that he's done after football is [with] the same intensity that he approached it during the game.

"I could probably train anywhere else, but it wouldn't be the same. He has experience and knowledge. It's an honor for me to go to that gym … it changes your mentality and your focus and your understanding of exactly what it takes to be successful at really anything that you want to do. But right now, all I want to do is football. It's my passion; it was his passion. You see the fire that he has for it and getting better and pushing us to be the best that we can be."

Kreutz no doubt is proud that Mustipher has kept the same mentality as a starter that he possessed as an unheralded undrafted free agent.

"I don't really think much has [changed] because every day that I come in it's the same hunger and passion and love and energy that I have for the game when I was an undrafted guy," Mustipher said. "I feel like I have a little bit more of an experience about the schedule, how to prep, what times I need to be doing certain things. I feel like that's where the experience comes in, but my mindset is still the same: still fighting, scratching and clawing because as quick as I got it is as quick it can go.

"So, the mindset is still the same, and it's really just, 'What can I do to help the Bears win?' It was the same when I was an undrafted guy. As long as I'm helping the Bears win, I'm probably going to have a job, you know what I mean? So, it's been awesome. Training camp every year is all football, and I love that. Best job in the world."