Why Is Usain Bolt So Fast?

Usain Bolt electrified the Beijing Olympics in 2008, breaking both the 100-meter and 200-meter world records to earn the title of World's Fastest Man. For an encore, at the World Championships the following year, he smashed those two records again. (He ran the 100m in 9.58 seconds and the 200m in 19.19 seconds.) As he prepares for the London Games, he's primed to defend his gold medals, having run the second-fastest 100 meters in the world so far this year (Bolt's training partner Yohan Blake recently set the fastest time with a 9.75). SI KIDS explores what makes Bolt so fast.

[Meet Usain Bolt's Biggest Challengers]
The Science of Speed
Going fast on the track isn't really about how quickly runners move their legs — it's about how hard their legs push on the ground, says Peter Weyand, a professor at Southern Methodist University and a leading expert in the science of sprinting. The harder a runner pushes off the ground, the farther he will propel forward. Most people push down with a force that is between two and a half to three times their bodyweight, but Bolt's legs hit the ground with nearly 1,000 pounds of force, which is almost five times his weight. Bolt is also exceptional because sprinters his size (6' 5", 207 pounds) usually can't push hard enough to move the extra weight they carry. But since Bolt can, his size becomes an advantage, allowing him to take fewer steps than his competitors to finish a race. "Bolt gets more bang for his buck with his longer stride," Weyand says.

World Record By the Numbers
TOP SPEED: 27.45 mph

TIME IN THE AIR: During the 9.58 seconds it took Bolt to finish the 100, he spent 5.29 seconds not touching the ground at all.

NUMBER OF STEPS TAKEN IN THE 100m: 41

MAXIMUM LENGTH OF HIS STRIDE: 2.85 meters (9.35 feet)

[How does Usain Bolt compare to past 100m champions?]

Could He Go Faster?
When Bolt set his world record, conditions were good, but had they been ideal, he would've finished with a time faster than 9.58 seconds. In Berlin, Bolt ran near sea level with a light breeze assisting him. At higher elevations there's less wind resistance, and even the maximum wind assistance allowed when setting a world record (two meters per second) can make a difference, says Jonas Mureika, a physics professor at Loyola Marymount University. Mureika suspects that if Bolt ran with wind assistance in a place like Mexico City, where the elevation is higher than 7,000 feet, he would have clocked a record-shattering 9.49 seconds!