6:01 AM ET

Pittsburgh Steeler running back Najee Harris is wearing black Crocs with Fast U buttons as he walks through the doors of O Athletik just after 9 a.m. There is a picture of Muhammad Ali on the back of his shirt. There is a backpack on the shoulder.

Harris fist-bumps his way to the back of the gym, where a small group of players, boxers and local athletes have gathered to stretch before the workout.

Harris traded his Crocs for a pair of Nike Air Max 270s while sitting in the back corner.

There are three different types of workouts in a day. He will run through a gauntlet of workouts in mid-July as he prepares for his second season.

"If we have to lift a truck up over our head, then that's what we're doing," said Cooper, who has worked with hundreds of athletes. He doesn't want to hurt himself, so he doesn't want to do it. He wants to learn it and get better at it.

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After leading all rookies in touches a year ago, Harris is poised for another big season, though his training camp has been truncated after an offensive lineman stepped on his left foot Matt Canada said that Harris' volume of carries probably won't increase, but that he will be a bellwether for the offense.

Harris spent the off-season working on his body. It strengthened him mentally and helped him fill the leadership void caused by Ben Roethlisberger's retirement.

Regardless of who else is in the huddle with him, he would be prepared to take a significant step in embracing leadership and responsibility. "That's where he is and what he's done and where he wants to go."

Harris defined leadership by finishing his workout as the sun was setting on an empty high school football stadium.

Harris said that if he's the last one on the field, he's working harder than everyone else.

Air Max 270

Najee Harris was focused on preparing to handle the type of workload he experienced last season, when he led all rookies in touches. AP Photo/Keith Srakocic

At the bottom of a steep, turf-covered hill behind the gym, Harris stands in his red, orange and yellow Air Max sneakers.

The 25-yard incline is the first hurdle of the day. In waves, Harris and the group hop, sprint, backpedal and bear crawl up and down the urban mountain, sweating profusely after a few reps.

The warm-up is still going on.

Harris has been a fixture at these sessions since he connected withPeterson. Harris was invited to attend Cooper's training sessions after he left Alabama.

Cooper watched Harris cool down after his first workout last year. He shook his head when he spit into his cup.

"He's going to be nice," he said. He works hard. He's going to be one of those guys who needs to be protected from himself.

Harris played more snaps than any other running back. Second year back Jonathan Taylor was the closest to the Colts. Harris played almost all of the offensive snaps. Taylor was the second to check in.

Even though he was one of the league's best three-down backs, he never played more than 75% of the offensive snaps.

He's a big boy, according to Peterson. I looked at him a number of times. This boy is thick. He isn't fat at all. He has big bones. He's large and strong. The legs and body are large. He is well put together. He's perfect for a runner.

Harris is training like he is going to be on the field for the rest of his life. He is sculpting his body into a hybrid force of power and strength. Put on a little more weight.

Harris was listed at 231 pounds a year ago. Harris said he weighed in at 243.

Cooper said that you need a certain amount of fat and weight for running. Najee is trying to locate that. If you only go up a few pounds and you look like He-Man, that's great. It's part of the equation.

HyperKO

Harris said he fell in love with boxing because of the way it pushes him to beat the man in front of him while being prepared to go 15 rounds. He sees parallels in football. ESPN

He slips off the black Crocs when he comes back to O Athletik after a quick lunch.

He replaced them with HyperKO boxing shoes.

Harris first contacted Cooper and Marshall about boxing a year ago. On his first day off from training, he showed up at the gym to ask for more. Harris wanted to keep going even though most in the group were resting.

Cooper said that he told him that he hadn't had enough. This is interesting. I said, "Let's put it in the box."

Harris is the only one in the morning workout group at O Athletik. He ties his shoes and rests on a bench in front of the ring while he tapes Harris and tugs on his boxing gloves.

Harris runs through a maze of heavy bags and works on endurance. He goes to the speed bag and then into the ring.

Marlen Esparza is training with Cooper in preparation for her fight.

Harris met a boxing mentor in Esparza. He started warming up with Esparza on the treadmill early on in his training.

Esparza said that Harris was strong. His balance is good. He knows how far away it is. He can calm down even though he is quick. The man has his heart rate correct. If you want to do something, you will do it.

NAJEE HARRIS WITH THE GROWN MAN STIFF-ARM 🤯

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