A superb video that shows graphically how much faster athletes have been running the 100 meter sprint from 1896 to 2012.

There are a number of factors to consider, including improved nutrition, track surfaces, footwear and much research in sports science.   Also, before 1970, only amateurs were allowed to compete in the Olympic Games.

Sources: "The Complete Book of the Olympics" by David Wallechinsky and Jaime Loucky, International Olympic Committee; Amateur Athletic Assocation; Photographs: Chang W. Lee/The New York Times, Getty Images, International Olympic Committee