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posted: 6/30/2014 12:52 PM

Which hand you use, flexibility may be in your genes

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  • Dr. Erik King, pediatric orthopedic surgeon at the Ann & Robert H. Lurie Children's Hospital of Chicago, meets with patient Rachel Montes, 11, of Elgin.

    Dr. Erik King, pediatric orthopedic surgeon at the Ann & Robert H. Lurie Children's Hospital of Chicago, meets with patient Rachel Montes, 11, of Elgin.
    Courtesy of Jan Terry, Lurie Children's Hospital


You wanted to know

"Why am I double jointed?" and "Why am I right-handed?" asked fifth-grade students in Elise Diaz and Caroline DiCentio's class at Prairie Trail School in Gurnee.

Can your very top finger joint slip in a shockingly solo maneuver, or can your thumbs stretch in impossible directions?

Kids call that being double jointed, but Dr. Erik King, a pediatric orthopedic surgeon at Ann & Robert H. Lurie Children's Hospital of Chicago, said that term isn't biologically possible.

"That phrase suggests there are two joints, or more than one joint. Being double jointed is a nickname for people who are very flexible," he said.

Dr. King said the main reason why some people are more bendable is because flexibility is in their genes.

"There is a genetic predisposition," he said. "We're all on a spectrum of people who are very flexible, like gymnasts, and those who are less flexible. Doctors call it ligament laxity. Ligaments are the body's rope that holds the joints together."

In general, young people tend to have amazing ability to move their bodies in many directions. All of us can become more limber with exercise, Dr. King added.

Handedness -- using mostly your right hand or mostly your left hand -- also seems to be linked to genetics, although no one has a specific answer as to why someone favors one or the other.

Most people, as many as 90 percent, are right-handed. Dr. King points out that society has designed nearly everything with right-hand dominance in mind.

Even though genetics seems to play a role in handedness, there are exceptions, like Dr. King. His father is left-handed and he favors using his right hand.

Dr. King told a story about a tennis player he knows who broke his right wrist, his stronger and preferred side. During his recuperation, the player gained an advantage when he developed his left-handed volley. As a result, he surprises opponents with a winning left-hand return.

"There are theories that your brain develops in a certain way that determines left- or right-handedness," Dr. King said. Kids who are injured on one side have a tremendous ability to adapt and develop the other side.

There are people who are equally right- and left-handed. That's called ambidextrous.

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