At 228 pounds at the Senior Bowl, he would have been projected to be a weak-side or nickel linebacker. To flourish in the middle, he had to add at least 10 pounds of weight -- and maintain his speed and quickness.
By the Scouting Combine a month later, Barrow had added most of the weight, checking in at 237 pounds. He added another pound by his Pro Day on April 9. He didn't run the 40-yard dash again, choosing to stand on his Combine time of 4.64 seconds, but he did try again in the short shuttle, and cut six-one-hundredths of a second off his time.
Barrow's extra mass was the correct kind: effective muscle, so he felt faster with the extra bulk.
"I think it helped my speed, as far as it was good weight," he said. "I think a lot of times in college, you put on bad weight, because you're eating fast food and you're doing anything."
He went to the IMG Academy in Bradenton, Fla. for his pre-draft preparation. IMG connected him with a nutritionist, and Barrow let a better diet and workouts transform him.
"They had a great nutrition system," Barrow said. "They kind of taught me how to separate things: my carbs and my proteins. They gave us a meal plan and I just followed it, and the game plan worked."
It's not done, either.
"The (Broncos') strength staff has been telling me that I've got a good frame; I can put more weight on it and not lose any speed," he said. "That's kind of the game plan, to get with the nutrition staff, to add on some more healthy weight and just try to keep progress."
With every added pound, Barrow looks more the part of the prototypical NFL middle linebacker, which dovetailed with his work Friday.
"I've been getting work at the 'Mike,'" he said. "I've been kind of cross-training, learning the 'Mike,' the 'Will' and the 'Sam,' but primarily today, the 'Mike.'"
As he lined up, the impact of his workouts and diet plan was apparent; the barrel-chested linebacker looked stronger than he ever had at LSU. But physical preparation is only part of making Barrow into an every-down linebacker. The rest comes on the field and in the meeting room.
"Just sitting next to guys like Danny (Trevathan) and Nate (Irving), guys that have played this game for a couple of years out here, they knew the insides and outs, and getting in those guys' hip pockets and learning from them, I feel like they're some of the best linebackers that I've been around so far, and I've only been around for three days," Barrow said.
"The knowledge that they have, and if Coach (Richard Smith) has a question, the answers roll out of them so fast, so I just know that they're in tune with the system. I plan on being like that one day."
But that, like adjusting to the speed of the NFL, a new role and a re-shaped body, won't happen overnight.
"It's going to come with time, come with a lot of learning," Barrow said. "I've got to learn the system first and get real comfortable to where I can use my speed. I feel like right now, there are some things I do know, but a lot of things I'm still guessing on, and still kind of working my mind through.
"So once I learn the system and can be able to move faster, I think that will be a key -- and my speed will just keep me on the field."