Meb Keflezighi, 36, a naturalized American 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 only 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 in 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 says she been an okay runner at Wheaton College, but didn't excel until she started working out with the Princeton running teams that she started to excel.
