Shameka Marshall won the silver medal in the long jump at the Pan American Games in Mexico last October. At 28, Marshall may be making her final push to be on the U.S. Olympic team. Julie Jacobson/AP hide caption

itoggle caption Julie Jacobson/AP

American Ariel Hsing competes against Canadian Chris Xu at the table tennis qualifying tournament in Cary, N.C., on April 20. Gerry Broome/AP hide caption

itoggle caption Gerry Broome/AP