Micah Herndon's head hung between his shoulders as he crouched on all fours. Staring down at the pavement before him, he placed one hand in front of the other and painstakingly inched toward his goal: the Boston Marathon finish line.
PHOTO GALLERY: See some of the best images from the 123rd Boston Marathon in a gallery at the end of this story
Despite suffering from severe cramps that had rendered his legs almost useless, the 31-year-old Marine veteran told The Washington Post that he was committed to finishing Monday's race "with no help" to honor the lives of three men he knew while serving in Afghanistan who were killed in 2010 after their convoy was hit by an improvised explosive device.
"Nothing against no one that got help, but I didn't want help," said Herndon, who survived the blast that killed the men. "I wanted to finish on my own because whatever pain that I was feeling at that time, or whenever, is nothing compared to the guys and the families that were lost over there."
Herndon and his determination have since been widely heralded as "inspirational" after several videos of him dragging himself toward the yellow-and-blue finish line went viral on social media, each garnering hundreds of thousands of views by early Tuesday morning. He completed the race in 3 hours 38 minutes.
"This is guts personified," commented Darren Rovell, a sports business analyst.
The resident of Tallmadge, Ohio, wasn't always an avid runner. Monday's race was only the third full marathon he's ever run, he said.
Herndon said he was drawn to running several years ago when he realized it provided him with the "release" he desperately sought. At the time, Herndon, like many veterans, was struggling to cope with transitioning back to normal life after spending four years on active duty in the Marines, during which he was deployed to Iraq and Afghanistan.
"It takes me to a place that helps me to forget everything," Herndon said, describing the activity as "therapy." "It's a temporary getaway from everyday life."
Among the things Herndon would like to forget are the events of Jan. 9, 2010 - the day a 400-pound IED took out a vehicle carrying his fellow Marines, Matthew Ballard and Mark Juarez, and British journalist Rupert Hamer, who had been traveling with the unit.
Juarez and Hamer were killed on impact. Herndon said Ballard, his best friend, later died of his injuries.
"Survivor's guilt, it's real," Herndon said. "I definitely have it because I was the lead machine-gunner on that convoy and I didn't see that bomb that was buried. I live with that every day."
He would go on to survive two other IED attacks, both of which targeted the vehicle he was in.
"There's a reason why I'm here," he said. "I'm just trying to find out what that reason is for."
But while he figures it out, Herndon has used running as a way to pay tribute to Ballard, Juarez and Hamer.
A photo posted to Facebook in February showed race bibs emblazoned with the men's last names. The bright orange Nikes that Herndon wore Monday had three engraved name plates affixed to the laces.
It was the memory of his fallen comrades that propelled him to the finish line in Boston, Herndon said.
For most of the 26.2-mile run, Herndon was on pace to finish in under three hours, and he hoped to qualify for the New York City Marathon in November. But things began to go awry when he hit Heartbreak Hill, the infamously challenging incline near the race's 20-mile marker.
The discomfort, he said, started in his Achilles' tendon and "just went up from there."
With a little more than four miles left between him and the finish line, the steadily growing pain in his legs became overwhelming.
"Both my legs just gave up," Herndon said.
But he soldiered on, shifting his focus to the three men for whom he was running. Herndon chanted their names out loud, ignoring the occasional odd look from passing runners.
"I kept repeating those names," he said. "The thoughts of their memories and their families flowing through the mind just like they always do."
As it was his first time running the historical race, Herndon wasn't exactly sure where the finish line was. He knew only how far he had left to go.
"I kept looking down at my watch and it was like Mile 23, Mile 23-and-a-half, I was like, can the finish line ever get here?" he said. "But I was running at such a slow pace, it took forever."
When Herndon's legs couldn't carry him any farther, he dropped to his hands and knees. At certain points, he even relied on his Marines training, resorting to a "low crawl," lowering his entire upper body to the ground.
Race volunteers flanked Herndon on the final stretch, guiding other runners away from him. After he crossed the finish line, he was immediately lifted into a wheelchair, CBS Boston reported.
Social media erupted with reactions to video of his finish, which was shared by major outlets such as ESPN and Sports Illustrated.
One viewer thanked Herndon for "showing America the true definition of honor and valor."
"Nothing but respect for this man," another person tweeted.
By late Monday, Herndon still hadn't fully grasped his viral fame.
"It's kind of overwhelming," he said. "I didn't expect it to be this big so fast, or even be big."
He said he hopes he can use the attention to shed light on the "broken system" that veterans have to deal with when they come home.
"If we can do something about it, that's all I care about," he said, urging others to find their own healthy outlets like he has done.
Though he's still recovering from Boston - he said on Monday he looked "like a baby deer trying to walk" - it won't be long before Herndon is back to pounding the pavement.
"I'm definitely getting back into it," he said, "because that's my therapy and you don't miss therapy."