Older people are more likely to fall because they compensate less well if they go out of balance and not just because of a gradual loss of strength or flexibility, according to new research.
Injuries caused by falls among the elderly use vast health-care resources annually, so understanding why they tend to fall could help reduce suffering and cut the cost of providing care, according to a research group at Pennsylvania State University.
Their study of this subject was published last month in the Jour- nal of Gerontology: Biological Sciences.
The aspects of balance that declined with age were not well understood, said Dr Semyon M. Slobounov, the assistant professor of kinesiology at Penn State. "A better understanding of the dynamics of postural stability in the elderly will hopefully lead to methods to prevent falls," he suggested.
The group used an experimental test rig to determine why falls occurred, pinpointing movements that induced falling and predicting the situations in which individuals lost stability.
Postural stability is measured by recording the changes in the pressure of the feet on a surface using a force platform. The researchers placed subjects aged from 60 to 99 on the force plate and recorded changes in foot pressure while the subjects stood for 20 seconds.
They were also asked to lean as far as they comfortably could in six directions to determine the limits of their functional stability boundary. In part the extent of this boundary is dependent on the geometric stability boundary established by the placement of the feet.
"When an elderly person tries to reach beyond operational limitations - outside their stability boundary - they fall," Dr Slobounov said. "They cannot estimate where they are spatially or where their limits are. They cannot tell how far they can safely lean."
The study showed that the stability boundary decreased with age and the extent of the boundary was not wholly dependent on either strength or flexibility. There was a clear decline in the ability to compensate quickly for out-of-balance positions, in turn leading to falls.
Unusually, the study found that stability did not continue to decrease in the over-90 group compared to the 80 to 90-year-old group. "There may be a ceiling effect in play in this situation," Dr Slobounov suggested.