Gary Morley and Lisa Cohen
Kayla Montgomery is a runner unlike any other.
Every time she competes in a race, she knows she'll collapse in a sobbing heap at the finish line.
Unable to feel her legs, she'll crumple into the arms of her athletics coaches. Ice-cold water will be applied to calm the misfiring nerve fibers blazing beneath her numb skin.
The teenager has gone through this post-race trauma for the past five years since being diagnosed with multiple sclerosis.
"Every day that I run, it might be my last day -- I could easily wake up tomorrow and not be able to move," the 19-year-old American tells CNN's Human to Hero series.
"My initial MS attack caused lesions and scarring on my brain and my spine that affects the areas that are in control of how I feel my legs. So when I am overheated the symptoms reappear because my neurones start misfiring more.
"You can never really get used to the lack of feeling and the change of sensation, no matter how long you go through it. Every time it is still a bit of a shock and it's scary -- it freaks me out a little bit."
After five to 10 minutes she's able to get back on her feet again and start walking around, albeit a little stiffly as feeling slowly returns to her lower body.
It sounds like a nightmare ordeal that would put anyone off an athletics career, but Montgomery is determined to pursue her running dream.
She's actually faster now than before her diagnosis -- which, she says, was a painfully long and uncertain process following an accident playing soccer, falling hard on her neck and tailbone.
"It was really scary. I was so young. Most people with MS aren't diagnosed until their mid to late 20s, 30s. There wasn't anybody my age to relate to and understand what I was going through," she recalls.
"It took so long to get back results and we were ruling things out and leaving MS as the last option. For a while they thought maybe it was cancer."
When the diagnosis finally came, it sent Montgomery into a spiral of anger, depression and denial.
She avoided confronting the issue with her parents -- Keith, a salesman, and mom Alysia, recently qualified as a nurse -- and younger sister Courtney.
"I tried to pretend I wasn't sick or anything -- I wanted to go on with life as normal as possible," Kayla says.
"Nobody at school knew, and we were not allowed to talk about it at home. I just avoided it at all costs, and that actually made it a lot harder.
"The first couple of years after my diagnosis were impossibly hard -- I was so alone and still really scared. It was definitely a darker time in my life."
Running has proved to be her salvation. After a short break, in which she received treatment that made the numbness temporary, Montgomery decided she was going to make use of her legs while she still could -- despite knowing that exertion would bring back the symptoms.
"I wasn't amazing by any means but I was eighth on the team, so if somebody got hurt then I was there! And I wanted to be there if they needed me, so I trained so hard all the time and that definitely helped to deal with the things I wouldn't talk about," she says.
Montgomery's determination to succeed won her the North Carolina high school state title in the 3,200 meters last year, as she ran the 21st fastest time in the U.S.
She was team captain at Mount Tabor High School, setting several age-group records, and also excelled off the track in cross-country.
Now a freshman on an athletics scholarship at Nashville's Lipscomb University, she is studying molecular biology and has dreams of becoming a forensic scientist.
But before a career in CSI beckons, Montgomery is making the most of her chance to run for the college team.
"Racing is one of the greatest feelings in the world. I love it," she says.
"Long-distance running is my favorite ... you have to have so much stamina, strength and determination. I like to push myself to my limits for as long as I can."
One of the big challenges is staying on her feet during a race. If she gets knocked over or falls, which sometimes happens, then it's difficult to get up again -- especially in the later stages.
"If it is a track meet you can't grab on to something, whereas cross country there might be a tree close by that you can pull yourself up on," Montgomery explains.
"It all depends on when I fall as to how it will affect the outcome of my race."
Montgomery trains three hours a day, six days a week, covering 60-75 miles.
Without being able to judge pace through her legs, she has learned a new way to run, by focusing on the movement of her arms.
The hard work is paying off. Lipscomb is a Division One university in NCAA competitions, giving her an elite platform on which to impress.
It's a long way from those early high-school days when she asked her coach, mentor and "second father" Patrick Cromwell about her chances of running at college level.
"He said, 'I don't know, you might be lucky if you can be a walk-on.' I was like, 'Well I'll show you, I'm going to run in college and not only that I'm going to run for a D1 school.' And I am!
"Lipscomb is one of the best, it's really awesome to achieve that once really far-fetched dream."
Montgomery was actively recruited by Lipscomb, the first school to contact her -- others also rang "but a lot of them never called back" after she explained her condition.
"They made me feel so welcome," she says of her first visit to Lipscomb's campus. "They all knew my situation and it didn't bother them, and they didn't acknowledge it or ignore it either. It was exactly what I was looking for."
Her debut collegiate cross-country season was a steep learning curve, but Montgomery helped Lipscomb win a fourth successive conference championship in November, placing 13th overall and seventh in her team in the 5 km race.
On the track, she was sixth in the 10,000 meters last weekend as Lipscomb's women's team finished third at the Atlantic Sun championships in Florida, its best result at the event -- and a continuation of its rapid improvement since Bill Taylor, who recruited Montgomery, took over the athletics program in 2007.
She says the coach has given her the confidence to keep pushing herself, having taken a chance on her even though he realizes she may not be able to fulfill the four years of her scholarship if her condition gets worse.
"I keep running because it makes me happy," Montgomery says. "It makes me feel whole and safe, just because I know as long as I am running and still moving, I am still OK."