Mantooth is a big fan of triathlons. He has volunteered at several in his hometown of Las Vegas. Watching from the sidelines, he wished he could be one of the athletes crossing the finish line.

"But how could such an unhealthy person become a triathlete?" he asked himself. "The journey seemed so overwhelming, but every one of those athletes, from the pros to the Joes, had to start somewhere, right?"

Thanks to encouragement from his girlfriend, Mantooth will soon get to cross the finish line in Malibu.

"I know that success and real change will come from hard work, but I'm committed to the miles of training that lie ahead," he wrote. "I'm ready to finally improve -- and downsize -- the person I see in the mirror."

Tabitha McMahon

Life hasn't been easy for Tabitha McMahon. At just 19 years old, the Indianapolis resident was diagnosed with ulcerative colitis, a type of inflammatory bowel disease. Symptoms forced her to quit school, and she spent several years in and out of hospitals.

"Blood transfusions, broken bones, mono, pneumonia, incontinence, painful joints, significant weight loss followed by significant weight gain, major abdominal surgeries and a temporary ileostomy left me physically weary and nearly defeated," McMahon wrote on her iReport submission.

"Nearly defeated" is the key phase. After having her colon removed in emergency surgery, McMahon slowly recovered -- marrying her college sweetheart, earning her degree, starting work in the nonprofit world and adopting a baby. Now she has her eyes set on new goals.

"First and foremost, I want to get fit. I want to lose these extra pounds and be healthy and active every day. I want to live a long life for my husband and 7-year-old daughter.

"I also want to reduce stigma around UC and other digestive disease(s). As you might imagine, this is not the stuff of cocktail party chatter. However, 1.4 million Americans suffer silently from inflammatory bowel disease. It's pretty astounding.

"I have spent many years convincing myself that to be active I can only work out in a gym or at home -- somewhere near a bathroom. ... No more. It's time to face these fears head on. It's time to get out of the gym and on the road."

Rae Timme

Rae Timme, a long-time prison warden for the Colorado Department of Corrections, will retire two weeks after the Nautica Malibu Triathlon. She's excited about her retirement, but wants to be in shape so she can enjoy quality time with her husband, three kids and seven grandkids.

"I have ... learned the past few years how truly precious life is, and that none of us can take our health for granted," Timme, of Colorado Springs, wrote in her blog. "I have lost my sister, my brother, both of my parents. I am the oldest of the four kids that my parents had -- our younger brother died of leukemia when we were kids -- and the only one that survived them. Sadly, the primary causes of death for my brother and sister were preventable."

Timme has read scary statistics about her profession: People who work in corrections have the second highest mortality rate of any job; on average, a corrections officer's 58th birthday will be their last. That motivated her to apply for the CNN Fit Nation team.

"I am a literal bundle of emotions," Timme wrote in the days leading up to the kick-off weekend trip. "I am excited beyond belief, humbled to have been selected from so many applicants, scared to death about being able to keep up with the youngsters on the team, and terrified of having to wear the tri shorts that came in the mail today in public.

"Most of all, I cannot wait to get started on this journey."

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