London Olympics | Track and field

United States runners, from left, Allyson Felix, Francena McCorory, Sanya Richards-Ross and DeeDee Trotter celebrate after winning gold in the women’s 4x400 relay.  (Wally Skalij / Los Angeles Times)

United States’ Sanya Richards-Ross, front, leads teammates Allyson Felix, DeeDee Trotter and Francena McCorory down the track after winning gold in the women’s 4x400-meter relay. Russia won silver and Jamaica bronze.  (David J. Phillip / Associated Press)

Allyson Felix takes the baton from DeeDee Trotter. Felix ran her leg in 47.8 seconds to give the U.S. team a big lead.   (Wally Skalij / Los Angeles Times)

DeeDee Trotter of the United States passes the baton to Allyson Felix.   (Wally Skalij / Los Angeles Times)

With a huge lead, Francena McCorory of the United States takes the baton from Allyson Felix. The U.S. relay team won by 3.36 seconds.   (Wally Skalij / Los Angeles Times)

Jamaica’s Usain Bolt pulls away from the United States’ Ryan Bailey to win the 4x100 men’s relay.  (Wally Skalij / Los Angeles Times)

Jamaica’s Usain Bolt celebrates the gold in the men’s 4x100 relay. The Jamaican team set a world record with a time of 36.84 seconds.  (Wally Skalij / Los Angeles Times)

Jamaica’s Usain Bolt celebrates winning gold in the men’s 4x100 relay. The United States was second and Trinidad third.   (Wally Skalij / Los Angeles Times)

Great Britain’s Mohamed Farah wins the men’s 5,000-meter race. He also won the 10,000m race earlier in the Olympics.   (Wally Skalij / Los Angeles Times)

Great Britain’s Mohamed Farah, right, leads the pack in the men’s 5,000-meter race. He won the gold medal with at time of 13:41.66 minutes.  (Wally Skalij / Los Angeles Times)

Anna Chicherova of Russia celebrates after a jump during the women’s high jump final. The Russian won the gold medal.  (Stu Forster / Getty Images)

United States’ Brigetta Barrett clears the bar and wins the silver medal in the women’s high jump.  (Wally Skalij / Los Angeles Times)

Brigetta Barrett clears the bar to win silver in the women’s high jump final.  (Matt Dunham / Associated Press)

Trinidad’s Keshorn Walcott celebrates after winning gold in the men’s javelin throw.  (David J. Phillip / Associated Press)

Russia’s Mariya Savinova celebrates winning the gold medal as she crosses the finish line in the women’s 800-meter race.  (Wally Skalij / Los Angeles Times)

Koichiro Morioka of Japan collapses after finishing the 50-kilometer men’s race walk.  (Dmitry Lovetsky / Associated Press)

Vera Santos of Portugal falls to the ground after finishing the women’s 20-kilometer race walk.  (Mike Groll / Associated Press)

A race walker competes during the women’s 20-kilometer race walk final.  (Feng Li / Getty Images)