Meb Keflezighi, 36, a naturalized American citizen, who won the 2009 New York City marathon and ran a 2:09:13 marathon in New York in 2011, is another top contender.
For the women, Shalane Flanagan, 31, has run in just one marathon, the 2010 New York City Marathon, where she finished second in 2:28:40. She also won the bronze medal in the 10,000 meters in the 2008 Olympics.
Another top contender is Desi Davila, 28, who placed second in the 2011 Boston Marathon in 2:22:38, which made her the top American finisher.
The American system of picking its Olympic marathon team is more democratic than the rest of the world. Most countries pick their runners by committee. However, 226 women and 161 men have qualified for the U.S. trials. Any American woman who has run a 2:46 marathon, 1:15 half marathon, or 33-minute 10,000 meters; and any American man who has run a 2:19 marathon, 1:05 half marathon, or 28:30 10,000 meters made the cut.
Samantha Howard, 25, is a high school teacher at Manheim Township High School and qualified during the 2011 Philadelphia Marathon - her first marathon - finishing in 2:45:45.
"It's been a goal of mine since I graduated college," said Howard, who ran track at Duquesne and currently trains with the Downingtown Running Club. "It was also a matter of staying healthy because I was injured in college. I knew physically I was in the shape to do it. As long as I could keep myself together, I could do it."
Her goal is to run a 2:43 marathon in Houston, and keep training for the 2016 Olympic Trials Marathon.
Lisa Baumert, 24, balances training with graduate school at the Princeton Theological Seminary. She said she had been an "OK" runner at Wheaton College, but didn't start to excel until she started working out with the Princeton running teams.
"At Princeton, I just really increased my mileage and my training, jumped into the team blindly, probably getting over my head a lot of times."
