Logan Carson didn't know Adrienne Cooper, and Cooper knew only what she'd heard and read about the 10-year-old boy before they met at a youth motorcycle race near Phoenix in November 2014. But it was a day that would change both of their lives dramatically.

Cooper, now 25, was a two-time ATV racing national champion and a self-described "adrenaline junkie." She'd had her share of injuries along the way, the worst being a 2011 crash that left her with a fractured elbow, tailbone and T12 vertebra and "a gnarly concussion." The sport had taken her around the U.S. and as far away as Australia, Ecuador and France.

"For a long time, racing was my life," says Cooper, who grew up around fast machines because her father competed in truck events like the Baja 1000 in Mexico. She won her first national title in 2006, turned pro in 2007 and won the AMA ATV motocross national women's title in 2012.

And Logan? He was friends with Cooper's nephew, Jeremy Garcia, who had invited Logan and his family to that day's race. As Cooper watched the boy asking Jeremy's dad to start Jeremy's bike and let him sit on the seat so he could gun the throttle, experience the bike's engine as it vibrated and growled, Cooper was struck by Logan's spirit. Nothing she'd ever endured was close to what he'd been through.

By the time Cooper met Logan, he'd become pretty good at scrambling around on a prosthetic leg after months of physical therapy. But he'd lost his right eye because of a blood clot and wore an eye patch decorated with a superhero sticker. His right leg was amputated just above the knee. He'd lost several fingers on his right hand and some toes on his left foot. His skin was scarred from multiple grafts.

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All told, Logan had spent 6½ months in hospitals being treated for a variety of complications since 2012, when a bout with strep throat developed into a near-fatal case of septic shock that shoved him into kidney failure. He's endured temporary heart failure, a rare blood-clotting disorder and more than 25 surgeries after his immune system began attacking his limbs to preserve his vital organs and brain.

He'd also been on dialysis nine hours a night for nearly three years and needed a kidney transplant.

Cooper knew all that because her sister, Teresa Garcia (Jeremy's mother), had met Logan's family through a mutual friend and was helping raise money to defray the Carson family's medical costs. 

"But the impact is a totally different thing when you see him in person, because it just puts it in reality," Cooper says. "You see sick people on TV. ... But I never met anyone like Logan. Right off the bat, he wanted on my nephew's bike like, 'I want to feel what this is like.' Then before the race, he was rubbing his fingers on my nephew's bike and he said, 'I'm putting my good luck on you.' That blew me away too.

"Here I was thinking, 'This must be the most unlucky kid I've ever met.' And he basically said, 'No. No, I'm not.' And I guess I fell in love with the little guy that day."

The Carsons already had found a kidney donor for Logan, and the woman was undergoing testing to see whether she was a match.

"I wasn't even a registered donor," Cooper says. "I never knew about it, never thought about it. But I told Logan's mom that day, 'I don't know how it all works, but if your other donor isn't a match, I'll be your backup. I'll donate one of my kidneys.'"

Jamie Carson, Logan's father, laughs now and says, "We had only really chatted with Adrienne a little at that point, but we'd made small talk with a lot of people at the race that day. So when she said 'I'll donate a kidney,' literally an hour after we met her, I was like, 'Wait a minute -- who are you again?'"

Cooper meant it -- even though she understood it would mean giving up motocross racing.

Just like that, the lives of everyone involved pivoted unexpectedly.

"To me, Logan is a rock star," Cooper says. "Here's this kid that's missing a leg, missing an eye, he's been to hell and back, and he's like, 'Nothing I have is going to slow me down. I can do anything I want.'"

The admiration is mutual.

"I don't think I'm special," Logan insists. "I think Adrienne is."

There are more than 122,000 people on the wait list for organ transplants in the U.S. and about 300 new transplant candidates are added each month, according to data kept by the Organ Procurement and Transplantation Network, part of the U.S. Department of Health and Human Services. A list of frequently asked questions, including how to be a donor, can be found here.

Some states try to make it easy for people to register as organ donors while renewing their driver's licenses. Former Green Bay Packers running back John Brockington, through his foundation, is among those attempting to address the disproportionate need for organ transplants in minority communities.

Logan's case underscored the difficulties that families go through as they sit on the wait list.

The first volunteer wasn't a match.

When the Carsons got that news, about two weeks had passed since they'd first met Cooper. As much as they were moved by her offer, they had learned some hard lessons during Logan's many health setbacks. As Jamie says, "You learn not to allow yourself to get too high, because the fall is too great."

Before his current career as a division manager for a machine rental company, Jamie was a U.S. Marine. Logan was born while Jamie was on a combat tour of Iraq that took him to hot spots such as Baghdad and Fallujah. He and Candy lived with the constant terror of never knowing whether he'd make it through the day unharmed.

But watching their son fight and fight to live, and then to get stronger, and then to walk again on his prosthesis, and then wait for a donor -- all of that was a different kind of anguish. Candy says she cried even at positive milestones, like when Logan walked around his hospital bed on his new prosthesis using a walker for the first time and then triumphantly told her: "I am going to give myself a Cheetos. Because I deserve it."

They had all been through so much already.

"So when Adrienne said 'Well, I'll donate Logan a kidney,'" Jamie says, "I just looked at her almost like, 'OK. Whatever. ... You're not loaning us your favorite baseball card or something like that -- this is serious business.'

"Again, we only knew her about an hour by then and, you know, I thought, 'I don't want this to get weird for us when I call and say, 'OK, you're up next. Where's your kidney?'"

So it was with some trepidation that Candy texted rather than called Cooper and asked, "Did you mean what you said the other day at the race?"

Cooper, who was at work, immediately texted back just two words: "I'm in."

The Carsons' wait-and-see attitude seemed wise when tests initially suggested Cooper wasn't a suitable donor. But Cooper, who was new to the roller-coaster ride, says she was "devastated." Fortunately, a doctor thought there might have been a glitch with the test and asked Cooper to repeat it about a week later. That's when she was confirmed as a match.

"When I got the call at work," says Cooper, a team leader at Dun & Bradstreet, "I hung up and just yelled. And all my co-workers knew what was going on and love Logan as well, so some of them started yelling, too."

The transplant surgery took place on March 31 -- less than five months after the first meeting. Cooper was rolled into surgery at the Mayo Clinic in Phoenix and afterward her kidney was transported about 15 miles to an operating room at Phoenix Children's Hospital, where Logan would have the transplant surgery.

The kidney failure Logan had been living with wasn't life-threatening -- yet. But it did affect his health and impact his entire family.

After Logan barely survived the septic shock in 2012, he was airlifted to Ready Children's Hospital in San Diego because the burn doctors there were best qualified to handle the necessary amputations and skin grafts. The Carsons ended up having to stay in San Diego for 4½ months.

Candy took a leave from her Phoenix-area veterinary practice. Jamie's employer at the time continued to pay him even when he couldn't work. The Carsons lived for a while in their camping trailer and brought their dog along to make life seem less uprooted for their other son, Bryce, then 5. They eventually moved into the Ronald McDonald House across the street from the hospital. They were still there when Bryce started school for the first time.

Candy says Logan will need additional kidney transplants throughout his life because he is so young. But his quality of life is vastly improved already. His appetite and mental sharpness are back. The dialysis he used to receive involved a tube being connected to a catheter in his stomach to cycle two large bags of fluid through his body as he tried to sleep. If Logan rolled over and pinched off the tube, an alarm would sound, and Jamie or Candy would have to get up and roll him over. That made for many sleepless nights.

"It's nice to not have to worry about that anymore, too," Candy says.

Cooper's extended family and the Carsons have a strong bond now. But the one between Adrienne and Logan runs deepest of all.

"I don't know if you believe in God or not," says Jamie. "I didn't at the time. But looking back now, there have been so many amazing coincidences, so many things that turned out so incredibly perfectly, so many people that helped us. ... To meet Adrienne that day, to see a stranger give up her kidney for someone you hardly know, to stop racing -- that is something I just can't comprehend. She's super special to us."

Cooper, like Logan, came through the surgery fine. But she had to give up motocross because the risk would be too great for her to injure her remaining kidney, "and then I [would be] the one needing a transplant."

Before she met Logan, Cooper had been pulling back on racing, but her plan had been to compete for at least another five years. That all changed.

"I felt bad when Adrienne felt she had to give up her motocross career for this," Candy says. "But Adrienne still has her fun. She's still an adrenaline junkie. She even made Logan promise that if she donated her kidney to him, he'd go sky diving with her."

To feed her thrill habit, Cooper and her dad still have an 850-horsepower sand buggy they fly around in, too. "And riding in it is the thing I love to do most after motocross racing," she says.

Like Jamie, Cooper believes there's been something "mystical" at work since that day she met Logan and that he came into her life for a reason.

Cooper says before meeting Logan, "I was always just about me, my racing. That was No. 1 for me -- my racing, my results. ... I was so incredibly selfish when I was 18. I was just so driven. But now I have things I care about beyond my results. I'm super huge into organ donation efforts now. This just changed my perspective on a lot of things."

Cooper concedes now that she and Logan are past the surgery she sometimes misses motocross. But the pang doesn't last.

"As much as I loved racing, giving it up to do this was actually an easy decision," she insists.

"I mean, yes, it was my life. But that was nothing compared to knowing the choice to help Logan could make or break his."

Johnette Howard is an award-winning writer and author who previously worked for Sports Illustrated, The Washington Post, and Newsday. She contributes general sports columns to ESPN.com and ESPNNewYork.com.