No one at the Planet Fitness in Maryville, Tenn., seemed to know Jason Harding last week.

But after the 15th anniversary of the Sept. 11 terror attacks, everyone at the gym — as well as hundreds of thousands of others around the country — know of the emergency responder who walked into the Planet Fitness early Sunday morning, before his shift at work, and asked to use a stair climber.

In full turnout gear, Harding then climbed the equivalent of 110 flights of stairs to honor those who died on 9/11.

“I did it because it felt right,” Harding told The Washington Post.

Each year at National Stair Climb events, fire-service members across the United States honor 9/11 victims on Sept. 11 by climbing the equivalent of the 110 stories of the World Trade Center.

Harding has attended Nashville’s Memorial Stair Climb for the past four years, but was unable to do so this year because he had to work.

So he decided to pay his own tribute by going to a gym and doing the climb there.

His local gym, however, wasn’t going to open until noon Sunday, and Harding had to be at work near Knoxville by 8 a.m. So he went to the 24-hour Planet Fitness in the nearby Smoky Mountains foothills community of Maryville at about 6 a.m.

Moved by the tribute, a staff member took a picture of Harding while he was on the exercise machine and posted it to her Facebook page.

“This man asked if it was okay for him to climb 110 sets, fully suited, of stairs in honor of his fallen brothers and sisters for 9-11. Yes sir, you can,” Lezlie Bauler, a front desk associate for Planet Fitness, wrote on Facebook as she posted the picture. “I am not one to get emotional, but a few tears were shed. Thank you for your services.”

That picture has since been shared more than 150,000 times.

Kali Roscoe, a regional manager for Planet Fitness, said she did not expect Bauler’s photo to go viral.

Harding said he has received multiple messages from people expressing their support and gratitude. Some said his act “brought them to tears.”

“That was probably the most emotional thing I’ve been through in a really long time,” said Harding, a public safety officer for the Metropolitan Knoxville Airport Authority who has served on the fire department in Fairview, Tenn.

Spending 42 minutes on the stair climber “is so small” compared to the dozens of Stair Climb events held across the country, he said. Proceeds raised at those events go to victims of the 2001 attacks and their families.

He said he would like for others — firefighters or not — to also pay tribute to the victims of the terrorist attacks, and perhaps post their own pictures on social media, with or without turnout gear.

In a statement, Harding thanked “everyone that shared and commented in response to this post. It it proof that although we seem divided as a country at times, we unite at the most crucial times.”

Bauler shared only a few words with Harding that day.

Before he left the gym, Bauler let him know that she had posted his picture and that it was starting to spread.

“I was just really moved,” Bauler told him.

Harding thanked her for sharing the photo, then left to go to work.