Steelers fans have seen it if they follow him on any form of social media. He has posted his workouts on Twitter, Instagram and Facebook, amazing people with his sheer physical strength.
I've seen it when I've walked into the Steelers weight room, a no-nonsense approach, just a simple attack on every weight within reach.
James Harrison doesn't just work out, he works out with an intensity, passion and love for it that is hard for any athlete, in any sport to come close to matching.
"It's not a game where you are able to just come to work on Sunday and think that everything is going to just roll out the way it was planned," said Harrison. "It's a physical game. You have to put the physical work in to prepare to play."
And Harrison does. He is the poster child for how to keep in shape during the season and in the offseason, keeping himself in better condition than the vast majority of 21-year olds just selected in the NFL Draft, despite the fact that he turned 37 today, May 4.
"Coach (Dick) LeBeau told us a long time ago, 'I want you to pray as if everything depends on it, but I want you to prepare yourself as if everything depends on you,'" said Harrison of how he keeps going so strong. "Through that prayer and preparing myself, God has blessed me. I have been able to be healthy and I have also prepared myself to be in position to do what I am doing."
What he is doing is preparing for his 13th season in the NFL, and happily for Steelers fans, another one in the black and gold. During free agency Harrison was faced with a decision, sign back with the Steelers or follow LeBeau, his long-time defensive coordinator, to the Tennessee Titans. It was a decision he gave a lot of thought to, and in the end he knew Pittsburgh was the place for him.
"It came down to basically my family was here, I had been here for most of my career," said Harrison. "My legacy would be here. The principles of the game, which is a business, it would have been a bad business move to go to another city for the same amount of money I would get here.
"And the fans. Steelers' fans are the greatest fans in the NFL. The love for their team, understanding of the game and their enthusiasm made my decision even easier."
Harrison's NFL journey has been well documented, going from an undrafted rookie who had been cut multiple times to a Pro Bowl linebacker. He spent his first 10 seasons with the Steelers, before playing for the Cincinnati Bengals in 2013. At the start of the 2014 season, Harrison decided his playing days were over and retired from the NFL. A few weeks later injuries at outside linebacker had him back in action with the Steelers.
When the 2014 season ended, those on the outside thought Harrison's Steelers' days were over. But those inside the Steelers' organization knew he would be a key part of the defense this year, especially with the departure of other veterans. The release of defensive end Brett Keisel, and the retirement of safety Troy Polamalu and cornerback Ike Taylor, left Harrison as the elder statesman not just on defense, but on the team.
"You can't play this game forever," said Harrison. "It's a young man's game. For us to have the opportunity to play as long as we did, as long as those guys had, it was a blessing. At the same time it's hard to see them go, but it's part of the game. We have to be happy for what we had and go from there."
Harrison, who recently has been taking part in voluntary workouts at the team's practice facility, spent the majority of his offseason working out with his trainer in Arizona. After witnessing his workouts all year, some of the team's younger linebackers, including Ryan Shazier, Jarvis Jones, Vince Williams and Sean Spence, asked him about the offseason regime, and then joined him in Arizona.
Take a look at some of the best photos from the career of Steelers linebacker James Harrison.
"That was through the course of the year, watching what I was doing, asking who I was training with," said Harrison. "I told them what I was doing, where I was doing it. They wanted to come out there, meet with the trainer and do it. We made a plan at the end of the season to come out there and work out. I did see they are definitely physically getting stronger. There is growth there."
Harrison, who doesn't necessarily look at himself as a leader, quite simply is. His work ethic is impossible for younger players not to pick up on, not to learn from. If they don't learn from him, don't try and emulate what he does, then honestly, it's their loss.
"I go out and put in the work I feel is necessary," said Harrison. "I try and lead by example. Sometimes I get a little more vocal than others. But I try and lead by example and I think that is the best way to do things. If guys happen to want to follow along and do the same thing you are doing, that is great."