Apr. 01, 2011

Science Dad on the Sense of Balance

by Vince Harriman

Beckett learned to ride a bike this spring, so we've been talking a lot about his sense of balance. Learning to ride a bike is one of those strange activities that you just have to do in order to do it. How do you learn to balance? You just do it. I have spent many many hours on bikes over the years, but I can still remember the very first time I rode a bike as if it were yesterday. That very first ride ended in a crash, but it was thrilling, and after that I could ride a bike. In the midst of all the conversations Beckett and I have had about balancing on a bike, he somehow hit on the one question that could tie it all together -- "Why do surfers hold their arms out?"

Eyes Open

Eyes Closed

Surfing (and skateboarding, and razor-scootering, and roller-blading) is a lot like cycling -- you try and try and try to do it, and then you just do it. All of these activities are about balance, and balance is about one thing -- your brain trying to process where your body's center of gravity is. The way your brain does this is with a tiny bit of liquid deep inside your ear. Your inner ear has a structure called the semicircular canal -- actually a set of three tubes set at right angles to each other with hairs that sense the movement of the liquid. Tilt your head and the sensors tell your brain that your head is tilted. Tilt your whole body, and your sensors (along with your muscles) tell your brain that your whole body is tilted. Your body uses the information gathered in the inner ear and tells the muscles in your body what to do to remain upright. Your inner ear is constantly telling your brain where your center of gravity is, and what needs to be done to preserve an upright posture given the current state of your center of gravity.

Now the brain is amazingly sophisticated and very good at keeping people upright. Walking, running, even crawling and rolling over, the brain and inner ear sense the force of gravity and tell us what to do to maintain our posture. And most of the time, our body does it without our even being aware of it. But, why is learning a new way of balancing so scary and difficult? And why does a switch suddenly go off that let's us go in an instant from unbalanced to a state of balance? Part of it has nothing to do with the ears and everything to do with the eyes.

When Beckett was first learning to ride a bike, he was worried about crashing. I told him: "Look where you want to go, not where you are crashing or don't want to go. Look at the tree and you'll ride right into it." As soon as he stopped looking at the trees and fire hydrants and rocks, he was able to ride. As much work as our ears do to help our brain stay balanced, the eyes also give our brain a direct (and sometimes scary) input.

I asked a surfer friend what he could tell us about surfing, and the first thing he said was: "Don't look at your feet, look at the wave in front of you." If you want to learn how to balance -- whether on ice skates or a bike or a skateboard -- relax, look at the horizon, and let your ears and eyes do what they do.

You can do a lot of things to trick your brain, both to improve your sense of balance, and to disturb your sense of balance. I have some fun experiments you can try below. Do them, then get on a helmet and get out and ride!


1. We started with a simple experiment to answer Beckett's question about surfers. I had him stand, put his hands at his side, and lean to one side as far as he could. He didn't get very far before he lifted a foot and began to tip over. Next, I had him put his arms out (like a surfer) and see how far he could lean over -- he was able to lean much farther. We did the same thing balanced on one leg. Sticking our arms out allows our bodies to make many slight adjustments to our center of gravity -- when our arms are at our sides, we're like a tree, either balanced or not. With our arms out, our bodies can make tiny adjustments that allow us to remain in balance.

2. Try leaning over forward as far as you can without bending your knees. You can use a measuring tape and a friend to see how far you can lean. Then stand with your back against a wall and see how far you can lean forward without bending your knees. You probably can't lean over nearly as far. Why?

3. Here is a very simple experiment: time how long you can balance on one leg. Then, time how long you can balance on one leg with your eyes closed. Even adults will find that they can't stay balanced as long with their eyes closed.

4. In a clear open space, spin around for thirty seconds and stop. How dizzy are you? Is it hard to stay balanced? Now spin around for thirty seconds with your eyes closed and keep them closed when you stop. It should be much harder to stay balanced. When you spin, you slosh the liquid in your ears around and when you stop, your eyes help you regain your balance while the liquid stops moving in your ears. When your eyes are closed, they can't help the brain process the signal from your ears.

5. Bend over at the waist -- again keeping your legs straight -- and see how far you can reach. Then bend forward, but kick one leg out behind you as you bend to act as a counter-balance. Your body (and ears and eyes) will adjust for you, and you should be able to lean farther forward with a leg out. You can also try this leaning over sideways.

About Vince Harriman

Science Dad, AKA Vince Harriman, is a freelance writer living in Annapolis. His two sons, Beckett-6 and Rowan-2 1/2 ask him 'why' approximately 6,542 times a day.

The views expressed are those of the author and are not necessarily those of Science Friday.

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