Justin Legg could dead-lift a washing machine and carry it across the street. He could swim miles on end and run a marathon on one day's notice.

The former Navy SEAL stayed in top shape because his life -- and the lives of his teammates -- depended on it.

But when his physical strength deteriorated in a fight against cancer, Legg had to rely on his mental fortitude to carry him through four years of excruciating pain, a bone marrow transplant and two collapsed lungs.

Finally back on his feet, Legg now has a new mission. He's relearning to run, one step at a time, in honor of the 19-year-old boy who saved his life.

Newlywed nightmare

The pain started in his ribs. Legg brushed it off, figuring a martial arts fight had gotten the best of him.

He and his new wife, Suzanne, were enjoying their first few months of marital bliss in Louisiana. He was rebuilding their house -- the one that Hurricane Katrina had destroyed -- in between training at a military base in Mississippi.

But the pain persisted and his workouts soon started to suffer.

"For me it was pretty easy to run 10, 15 miles," Legg says. "Suddenly I couldn't run five. I got to three and my legs just ground to a halt."

In June 2006, shortly before his 28th birthday, Legg's doctor called and told him that his white blood cell count was elevated. The military sent Legg to the National Naval Medical Center in Bethesda, Md., to get checked out.

The diagnosis: acute lymphoblastic leukemia.

"My first question was, 'Can I still be a SEAL?'" Legg remembers.

Still in shock, Suzanne was ticked off: "Not 'My new bride' or 'What's our new life going to be like?' but 'Am I going to be able to roll in the dirt with my friends and blow up things?' My whole world in front of me just went black."

Doctors immediately started Legg on eight straight days of chemotherapy. The drugs had no mercy -- attacking healthy and unhealthy cells alike, weakening his entire body.

"They tell you to take your IV pole and walk a lap around the floor each day to avoid clots," Legg says. "I remember leaning on that IV pole, just draping my arms over top of it just to get around the ward once."

That didn't stop him from doing lunges in the hospital library, using books as weights.

In addition to leukemia, doctors discovered Legg had the Philadelphia Chromosome, an abnormality in his genes that caused cancerous cells to duplicate 80 times faster than in other patients.

Chemotherapy wasn't going to be enough; he needed a bone marrow transplant.

Attacked from within

Like many SEALs, Legg is a little "twisted," Suzanne says. He's stubborn. Intense. Arrogant.