Fresh off a 12-week stint in California with veteran performance coach Scot Prohaska, McClellin dropped 11 pounds and 8 percent body fat in the offseason in anticipation of his much-anticipated move from defensive end to linebacker.
McClellin currently checks in at 252 pounds with 10 percent body fat, while running a 4.5 40-yard dash and bench-pressing 365 pounds.
"He knew it was a big year for him and wanted to perform for his teammates, the fans and the organization," Prohaska told ESPNChicago.com on Monday. "He felt deep inside this [linebacker] is where he always belonged. He was really motivated to prove to everybody that this is where he belonged."
Prohaska, who is based in Huntington Beach, Calif., has worked with professional athletes in a variety of sports for 20 years.
"I've known about Shea because his agent is a friend of mine and I actually help with some of his combine guys," Prohaska said. "I watched Shea this year and there was obviously a little concern about his performance. He struggled a little bit up and down the defensive line. I've been kind of eyeing him this last year but I've only known him for this offseason.
"So I evaluated him and took a look at a lot of his stuff in college at Boise State. I realized he was missing a couple of strengths or strength qualities you need for football. He's a springy guy, so in space he can get around you. But when he would lock in with a player, he didn't have the isometric strength or back strength to drive past the guy and disengage."
Prohaska said McClellin completely bought in to his program and moved to California with his wife for the three-month training session. The workouts ran five days a week for three hours a day, not to mention the nutritional part of the plan that McClellin had to adhere to.
McClellin never missed a workout.
"The first hour of the workout would be all movement-based stuff, linebacker stuff, drills -- really teaching him how to drop his hips and move in space," Prohaska said. "It was all multidirectional stuff. In the later afternoon we would hit on real critical strength stuff he needed; other days it was explosive strength."
The Bears think moving McClellin to linebacker will revitalize the first-round pick's career after he recorded just 6.5 total sacks in 2012 and '13 when he lined up at defensive end. McClellin is expected to compete for the starting strongside linebacker's job, but the Bears could decide to move the athletic McClellin to different spots during a game if the defense sports a more hybrid look.