Ryan Hall and Meb Keflezighi headline the men's field for the U.S. Olympic marathon trials this morning in Houston.

Shalane Flanagan and Magdalena Lewy Boulet, members of the 2008 U.S. Olympic team, lead a deep women's field.

A total of 113 men and 188 women are competing for three spots for each team that will run in London this summer.

The runners will start downtown, then make three circuits around an 8-mile loop.

Turlock's Miguel Nuci, who finished 15th in the 2007 Boston Marathon, also will be on hand to compete for a berth on the 2012 Olympic team in London. \

The trials will be aired today at noon on NBC.

See video below