For the elderly, falling is the leading cause of death due to injury. A biomedical engineer has been studying how vibrations can help seniors keep their balance. His work won him a Macarthur Foundation fellowship for creativity.
Shoes that shake. I'm Bob Hirshon and this is Science Update.
Every year, more than a third of all senior citizens fall and hurt themselves. Now, Boston University biomedical engineer Jim Collins and his colleagues think they've designed a solution to this problem: vibrating insoles. They tested the insoles on people both young and old.
We found that we could take the elderly subjects, whose mean age was about 75, and by introducing this noise, or weak vibration on the soles of their feet, that we could make them sway similar to somebody in their early 20's.
Collins says everyone sways a little when standing. But nerve cells keep track of the changing pressures on the soles our feet, and signal the brain to restore balance when we lean too far.
But in older adults, these nerve cells have lost much of their sensitivity, so seniors sway a little farther off balance before the cells register movement.
Collins says the vibrating insoles work by amplifying these changing pressures. This allows the nerve cells to respond more quickly.
Our primary goal is to develop a pair of inexpensive insoles that could be given to older individuals, and that these insoles would serve to reduce their incidence of falls, as well as improve their balance and walking so that they could increase their independence and general activities of daily living.
I'm Bob Hirshon for AAAS, the Science Society.
Making Sense of the Research
If a parent, teacher, or drama coach criticizes you for fidgeting, you can fire back with this fact: It's scientifically impossible for a human being to stand completely still. Even if you're as steady as a guard at Buckingham Palace, your muscles are constantly making tiny adjustments to keep you from toppling over. It's similar to the tiny adjustments drivers have to make to the steering wheel in order to keep going straight.
Your body makes these adjustments unconsciously, based on feedback from the sensory nerves in the soles of our feet. It takes information about how much force is pressing on different parts of your foot, and sends signals to your muscles about how to compensate. The result is a constant loop of swaying, adjusting, and then swaying another way.
The problem as you get older is that your feet, like most other parts of your body, become less sensitive to sensory input. Specifically, your threshold for sensory perception goes up. The threshold is the boundary between a signal that's strong enough for your sensory nerves to perceive and one that isn't. You can see this easily in hearing: whispers and quiet sounds that are well within the threshold of a teenager's hearing may be below the threshold of her grandmother's. The same thing happens with touch. The same small pressure on the foot that might be enough to trigger a young person's sensory nerves may be too weak to provoke a reaction in an older person.
Collins' vibrating insoles work by generating small, random vibrations all over the sole of the foot. Although these vibrations are too weak to consciously feel, they boost the overall level of stimulation to the soles of the feet. As a result, weak pressures triggered by swaying are added to the pressure of the random vibrations, which makes them strong enough to clear the threshold and trigger the sensory nerves. It's kind of like putting a kid on your shoulders so he can watch a parade: when his height is added to your height, he becomes "tall" enough to see over the other people.
Collins and his colleagues measured sway by attaching reflectors to several parts of their subjects' bodies and recording their movement with television cameras. The insoles helped elderly subjects more than younger ones, presumably because the younger subjects' feet were fairly sensitive to begin with. Collins says the invention could be especially useful to patients who have diabetes or a history of stroke, both of which increase the risk of falling.
Now try and answer these questions:
- What is the purpose of Collins' vibrating insoles?
- How do they protect users from falling?
- What is a threshold? How does it apply to this research? Can you think of other examples of thresholds in everyday life?
- The vibrations used in the insoles are very weak. Why? What might happen if they were strong enough to consciously feel?
The Exploratorium's page on Proprioception features short activities that demonstrate how the body balances itself.
The article Balancing Brains, by FirstScience.com, describes research that may help astronauts regain their sense of balance more quickly after long trips in space.
Vibrating Insoles Help People Regain Balance, from the New York Times, discusses a study published in January 2006 in The Annals of Neurology about the continuing research on these insoles.