Balance benefits from noisy insoles

If Granny has trouble keeping her equilibrium, it may be because her feet have become less sensitive to pressure changes. Boston scientists have found that they can diminish swaying in elderly people by sending subliminal, erratic vibrations to the bottoms of the seniors’ feet. This subtle postural therapy relies on a principle known as stochastic resonance, whereby noise improves signal recognition in a system such as the nerves (SN: 11/23/96, p. 330).

Pressure changes on the bottom of feet normally signal that the standing body is beginning to sway–movement that can lead to falls in the elderly. To reduce swaying, James J. Collins of Boston University and his colleagues developed gel-based insoles embedded with battery-powered mechanical vibrators, called tactors. Then, they asked volunteers to stand shoeless on these cushions with their eyes closed for a series of 30-second tests–20 trials for people in their 20s and 10 trials for those in their mid-70s. During half of each person’s trials, the tactors vibrated at intensities too low to be consciously felt.

Participants swayed less when tactors delivered their subtle, erratic drumming to nerves, the researchers report in the Oct. 4 Lancet. The decrease was 5 to 20 percent depending on how motion was measured. The oldest volunteers benefited most. Indeed, Collins told Science News, “we were effectively able to take 75-year-old individuals and, by introducing noise, improve their balance to the level of 20-year-olds.”


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Janet Raloff is the Editor, Digital of Science News Explores, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

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