University Park, Pa. -- The loss of strength and flexibility is not the only reason why older people fall. A new Penn State study suggests a decrease in the ability to rapidly compensate for out-of-balance positions and their generally smaller ranges of stability may account for unsteadiness in older adults.
"The particular aspects of balance that decline with age and make older adults more prone to falling have not been specifically identified," says Dr. Semyon M. Slobounov, assistant professor of kinesiology in the College of Health and Human Development. "A better understanding of the dynamics of postural stability in the elderly will hopefully lead to methods to prevent falls."
By predicting the situations in which individuals will lose stability and pinpointing movements that induce falling, the researchers can perhaps recommend ways to avoid unstable situations.
Postural stability is usually measured by recording the changes in the pressure of the feet on a surface using a force platform. The geometric range of stability is drawn from the placement of the feet. The researchers placed subjects on the force plate and recorded changes in foot pressure while the subjects stood for 20 seconds.
"It is impossible to maintain the center of gravity motionless and a person attempting to maintain balance will spontaneously sway back and forth and side to side," says Slobounov.
The researchers also asked the subjects to lean as far as they comfortably could in six directions -- forward, backward, side to side and diagonally -- to determine the limits of their functional stability boundary.
"When an elderly person tries to reach beyond operational limitations -- outside their stability boundary -- they fall," says Slobounov. "They cannot estimate where they are spatially or where their limits are. They cannot tell how far they can safely lean."
The study, reported in the January issue of the Journal of Gerontology: Biological Sciences, found that age decreased the functional stability boundary, which was always smaller than the geometric stability boundary drawn from foot placement.
"Our experiments indicate that the functional stability region -- as measured experimentally -- is considerably smaller than the geometric stability region," Slobounov says. "It suggests that the geometric region defined by the position of the feet may not be as useful a predictor of the stability boundaries as has been previously postulated."
Working with Elena S. Slobounova, senior applications programmer; Dr. Karl M. Newell, professor and head of kinesiology, Penn State; and Sarah A. Moss, now at University of Wisconsin, the researchers tested the stability of elderly persons between the ages of 60 and 99, using force plate technology. They also incorporated a direct method to determine stability boundaries.
Unfortunately, a variety of sensory impairment occurs with age. The researchers tested the subjects with both closed and open eyes and, overall, found that an absence of sight did decrease stability. Arm position also affects stability. The tests run with the subject's arms in front at shoulder height showed that this also decreased stability.
The worst case was that of closed eyes and upraised arms, but interestingly, there was no change between the 80- to 90-year-old group and the over-90 group.
"There may be a ceiling effect in play in this situation," says Slobounov.
The researchers note that there are other factors besides sight and arm position that could reduce or enhance stability in standing for the elderly. Further investigation of functional stability with these factors will be the focus of future work.
EDITORS: Dr. Slobounov may be reached at (814) 863-3883 or at sms18@psu.edu by email.