Ryan Chalmers pushes his wheelchair across the country 3,300 miles to build awareness for the potential of all persons with disabilities...

(Ryan Chalmers, who was born with a birth defect called spina bifida, an incomplete closure of the spinal column...in his own words.)

(CNN) -- I started playing sports at a young age and gravitated toward wheelchair basketball and track.

In college, I decided to focus primarily on track and pursue my dream of going to the Paralympics. With the support of a great coach and team, I was selected as a member of Team USA and competed in track at the Paralympic Games in London in 2012.

On Saturday, April 6, I embarked on the most challenging journey of my life. I left Los Angeles, heading toward New York City in my racing wheelchair -- a 71-day journey of 3,300 miles.

While I didn't know what to expect or how my body would react to the demands of "pushing" the equivalent of two to three marathons a day, I knew one thing for sure -- I'd get it done. I committed to Push Across America as my way of giving back to Stay-Focused, an organization that has significantly impacted my life.

Stay-Focused offers a SCUBA certification program for teens and young adults with disabilities. I met Roger Muller, founder of Stay-Focused, in 2005, and was given the opportunity to learn to SCUBA dive.

For me, it was a chance encounter that changed my life. I love to dive and have been diving ever since. We do all our diving in the Cayman Islands, most often in Grand Cayman, which is one of the best diving destinations in the world.

I was chosen to be the first Stay-Focused mentor in 2007, a role that enabled me to assist first-time divers, and I am now actively involved in running the organization.

A few years ago, Muller and I were talking about ways to raise funds for Stay-Focused. He asked me if I thought I could push my racing chair across the country. My first thought: "If it would help Stay-Focused, I'm in."

And now I have honored that commitment by combining my passion for "pushing" with my tremendous desire to support Stay-Focused, an organization I will be a part of for many years.

In addition to giving back to Stay-Focused, I was motivated to encourage others to take on challenges and give back to individuals and organizations that have made a difference in their lives. I also wanted to build awareness for the potential of all persons with disabilities and disability sports.

During my Paralympic experience in London, where 80,000 fans cheered for me and my fellow Paralympians at each and every event, I was impressed with how the fans embraced us as athletes -- athletes first, Paralympians second.

In doing the Push Across America, I wanted to help promote disability sports in the United States and encourage people to view athletes with disabilities in the same way they view other athletes -- in other words, no differently.

Push Across America was a phenomenal experience. For the most part, the weather was good, and of course, there were mountains to climb. But I was focused and knew why I was doing it and I knew this would be a defining moment in my life.

I did it to prove I could and to encourage others to never give up, as well as to support Stay-Focused and to have a good time! My theme song is "No Surrender" by Bruce Springsteen. Yep, for me, I made a promise to Muller I swore to remember, and this was it --"no retreat, baby, no surrender!"