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November 11, 2003

Purdue researcher working to catch elderly before they fall

WEST LAFAYETTE, Ind. – To ease one of the most costly and growing strains on the American health care system, a Purdue University researcher is studying why and how elderly people fall.

Shirley Rietdyk and research team
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In the biomechanics lab, Shirley Rietdyk (pronounced REE-dike), professor of health and kinesiology and director of the lab, measures balance and mobility in older people. By studying the interaction between the body's neural and mechanical systems, she is learning how the nervous system combines visual and sensory information to coordinate muscle activity.

"No one builds a two-legged chair because it isn't stable," says Rietdyk, a member of the Purdue Center on Aging and the Life Course. "But that instability gives humans a tremendous amount of flexibility in movement, allowing us to carry items while walking, or even to do a cartwheel or backflip. How the body and the nervous system work together is thoroughly fascinating. Even the world's best engineers can't replicate the human form and its movement. Robots built in human form, such as the Honda robot, are awkward and heavy. They may be able to climb stairs, but they can't climb trees.

"Our mechanical systems, our bodies, are very unstable with a high center of mass, a small base of support, and three joints in the support limbs. Yet, we move about and interact with the environment. Disease or aging, on the other hand, may impair the body's balance control system and cause older people to be more susceptible to falls. The question is: Can we find ways to maintain mobility and quality of life for aging individuals?"

The best way to test how an older person's body reacts to falling is to disrupt their balance, since even people with poor balance can stand quietly without a loss of balance, Rietdyk says. In Purdue's biomechanics lab, Rietdyk's team studies the participants' movements, which are recorded by six cameras that capture infrared light emitted from diodes placed on their bodies. A computer-generated human figure allows the researchers to examine the subject's motions in response to a push from behind. A member of the research team acts as a spotter to ensure the research participant does not fall.

A force plate, a piece of equipment embedded in the laboratory floor, measures the amount of force the subject applies on the ground to maintain their balance. The amount of activity generated by the muscles also is recorded. Both younger and older adults are tested for comparison across age groups.

In another test, the subject steps up onto a curb, and then steps down. In this test, Rietdyk evaluates the foot clearance over the curb, the crossing and landing velocities, and the force applied to the ground during the curb crossing.

Results from the studies could lead to better ways to assess the mechanism behind a person's balance, which could help researchers find and correct problems. Traditional balance assessments – walking in a straight line heel-to-toe or standing on one leg while opening and closing the eyes – don't provide enough information to help identify the limitations of an older person's balance, Rietdyk says.

"When older people start to fall it can be disabling, even if they don't injure themselves," Rietdyk says. "Once they fall, they are often scared about falling again, and the fear may cause them to be less active. Less activity leads to decreased strength and coordination, ultimately increasing the likelihood of falling again. We want to prevent falls by understanding how the body controls balance and determining why that control changes with aging."

Rietdyk, who is working with three colleagues from the health and kinesiology department, will examine older adults' abilities to learn to prevent falls, their confidence before and after fall training, and their body's responses to falling.

Rietdyk says other research suggests that people may need to fall every once in a while to maintain the ability to safely stop a fall. For example, when older adults were placed in a situation in which they slipped while rising from a chair, researchers have found that within five trials the subjects learned corrective strategies, such as stepping correctly, to prevent the fall.

"The nervous system has a marvelous ability to learn, even at 80 years of age, and the research we are planning will examine the effectiveness of fall training," Rietdyk says.

Because the elderly population is growing, the nation can expect to see more older individuals suffer from falls, Rietdyk says. The annual cost for fall-related injuries is expected to be $85 billion by 2020. Currently, a third of those 65 years and older experience one fall a year, and half of those older than 80 fall once a year.

The Purdue Department of Health and Kinesiology and the School of Liberal Arts are funding this study.

Writer: Amy Patterson-Neubert, (765) 494-9723,

Source: Shirley Rietdyk, (765) 496-6703,

Purdue News Service: (765) 494-2096;


NOTE TO JOURNALISTS: Video b-roll also is available by contacting Amy Patterson-Neubert, (765) 494-9723,, or Jesica Webb, (765) 494-2079,


Shirley Rietdyk, Purdue University professor of health and kinesiology, watches her research team demonstrate how to apply force to 70-year-old Don Corrigan as part of a study to learn how the elderly maintain balance. Josh Williams, a senior in movements and sports science from Evansville, Ind., pushes Corrigan to simulate a loss of balance. Steven Torgerud, a second-year master's student in biomechanics from St. Paul, Minn., stands as a spotter. Mark Knezovich, a first-year master's student in health sciences from Peoria, Ill., monitors Corrigan's reactions on the computer. By studying the interaction between the body's neural and mechanical systems, Rietdyk is learning how the nervous system combines visual and sensory information to coordinate muscle activity. (Purdue News Service photo/Dave Umberger)

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