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STEVE INSKEEP, HOST:

If you've been following the Olympics at all over the past couple of weeks, you've probably noticed some extreme body shapes - from tiny gymnasts to enormous basketball stars. Those athletes are shaped by years of intense training, and also by the laws of physics. Here's NPR's Adam Cole.

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ADAM COLE, BYLINE: Back in 1929, the fastest man in the world was Eddie Tolan.

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COLE: Tolan was a Detroit native who chewed gum while he raced, and taped his horn-rimmed glasses to his head. He was a stocky 5-and-a-half-feet tall, and ran the 100-meter dash in 10.4 seconds.

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COLE: Today's fastest man is Usain Bolt. He's nearly a second faster.

UNIDENTIFIED ANNOUNCER #1: Nine-point-five-eight, smashing the world record! Unbelievable!

COLE: He's 6-foot-5. For decades, sprinters have been getting taller, propelled upward by a simple law of physics. Sprinting is, basically, a controlled, forward fall. Athletes with higher centers of gravity can fall forward faster. And the taller you are, the higher your center of gravity.According to some physicists, this is one reason that Bolt breezes past his shorter competitors.

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COLE: Swimmers are getting taller, too, but they're an entirely different kettle of fish. Picture Michael Phelps - impossibly long arms; short, powerful legs; and huge feet - that all help propel him through the water. Then there's the long, tapered torso. It's a shape seals and shipbuilders have perfected. And it means less drag, and a swifter flight through the water.

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COLE: Now let's go to the other end of the size spectrum, to gymnastics. Here, the physics of rotation reigns.

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COLE: Making sudden turns in the air requires a lot of strength.

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COLE: The less of you there is to turn, the better. So you want most of your weight to be muscle. It's no surprise gymnasts are small, and they have some of the lowest percentages of body fat in sports. Since the '60s, the body mass index of gold medalists has been getting smaller, not bigger.

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UNIDENTIFIED ANNOUNCER #2: No man has ever lifted 500 pounds in competition - a quarter of a ton. Look at the concentration on that face.

COLE: Weightlifters come in all sizes. North Korea's featherweight champion, Kim Un Guk, is 5-foot-2.

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COLE: Iranian hopeful Behdad Salimi weighs 360 pounds.

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COLE: But thanks to physics, they all have something in common: short legs and short arms. If you have shorter limbs, you don't have to lift your barbells quite so high.

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COLE: You can size up past record holders and today's Olympians - in all these events and more - at our website, npr.org.

Adam Cole, NPR News.

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INSKEEP: If you're strong enough to lift a device, or a mouse, you can go to npr.org and read our Summer Olympics blog, "The Torch." You can read about the run made by the first female track and field athlete to represent Saudi Arabia. You can continue following this program throughout the day on social media. We're on Facebook. You can also find many of us on Twitter, among other places. We are @MORNING EDITION and @NPRinskeep.

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