by Shirley S. Wang
New research into how we maintain our balance could help athletes and prevent falls among the elderly.
Scientists are finding that maintaining stability and balance with each step we take requires complex coordination of foot placement, arm movement, trunk angle and neck and head motion. That's because every step is different from the one before it. There are slight variations in stride length and width and the angle at which the foot hits the ground, as well as small shifts of weight in the torso. People's bodies when walking must constantly make minuscule adjustments to accommodate these variations.
Other research is exploring how the brain controls our balance, which isn't well understood. A recent study identified a pocket of motion-detector neurons deep in the brain that sends out an alert when the body moves in unexpected ways, such as after stumbling on a crack in the sidewalk. The alert triggers compensating reactions throughout the body aimed at helping us to not fall down.
"The cerebellum is computing unexpected motion within milliseconds to send information to the spinal cord to maintain balance," says Kathleen Cullen, a physiology professor who performed the study with colleagues at McGill University in Montreal.
The research on balance and stability could someday be used to help improve training techniques for athletes, such as skiers and gymnasts, for whom balance is critical, experts say. It also might be able to help doctors better predict people's risk of falling and lead to improvements in prevention and rehabilitation strategies. Falls are the number one reason for death and injury among people age 65 and older, according to the Centers for Disease Control and Prevention. More than two million older people went to an emergency room in 2010 because of a fall, the CDC says.
The body has three main systems that help us stay balanced. The visual system takes in information from the outside world and transmits it to the brain. The proprioceptive system, which incorporates sensory systems throughout the body, tells us how the body's parts are oriented relative to each other. And the vestibular system, located in the inner ear, focuses primarily on how the head is moving. Generally, if at least two of these systems are impaired, people tend to have trouble with balance.
As people age, the vestibular system becomes less sensitive. Instead, individuals tend to rely more on their vision, which is relatively slow compared with the vestibular system. As a result, older people don't process information as quickly to correct for missteps, Dr. Cullen says.
Sjoerd Bruijn, a post-doctoral researcher on the Faculty of Human Movement Sciences at VU University Amsterdam, has been mapping in a series of studies the tiny natural variations people make from one step to another to see if these can be used to indicate whether a person is unstable. Greater than normal variability, typical in older people, could indicate a higher risk of falling, he says.
Other research, at the University of Texas at Austin, tracked healthy people as they walked and ran and found that older individuals are more at risk from small variations in steps than younger people. Jonathan Dingwell, a professor in the department of kinesiology and health education, said younger people can more quickly adjust to the changes than the elderly.
The study was conducted by attaching reflective markers onto various parts of participants' bodies. The positions of the markers, which reflected infra-red light caught on cameras, were reconstructed in a computer to generate a digital image that allowed researchers to analyze the gait of the participant.
Dr. Dingwell plans another study to track the relationship between variability in steps and risk of falling, by deliberately tripping older people walking on a split-belt treadmill. To avoid injury, participants wear a full-body harness, similar to what mountain climbers wear, that is attached by ropes to the ceiling.
Whether walking more slowly helps to maintain balance isn't clear, and study results have been mixed. In one study of 10 healthy people who were faced with a moving platform that swayed from side to side, researchers found that more important than speed were shortening steps and increasing step width, according to research published in the Journal of Biomechanics in March.
Foot placement is the primary mechanism for maintaining side-to-side balance. But sometimes foot placement is constrained, such as when people are attempting to walk a straight line. Instead, people use other parts of the body, particularly the upper body, including flinging arms, angling the trunk differently and making adjustments in the head and neck that allow the body to stabilize, says Art Kuo, a mechanical engineering professor at the University of Michigan in Ann Arbor.
Less clear is how the brain controls balance. After implanting electrodes in the brains of monkeys, McGill's Dr. Cullen and her team have identified, for what is thought to be the first time, neurons in a small region of the cerebellum that respond to unexpected motion and alert the body to react. For instance, if a person starts to trip, the neck may flex to keep the head stable, the torso becomes more rigid so that the body remains upright and the legs and feet take a stutter step, she says. The study was published in May in the journal Current Biology. Dr. Cullen says additional research is planned to try to identify how the brain calculates when unexpected motion is happening.
After a fall, older people often say they tripped or slipped. Researchers at Simon Fraser University, in Burnaby, British Columbia, wanted to observe what really happens. The team outfitted a long-term-care facility with video cameras and recorded residents going about their daily lives. They recorded 227 falls from 130 individuals over about three years. Tripping caused just 1 out of 5 of the incidents. The biggest reason for falling—accounting for 41% of the total—was due to incorrect weight shifting, like leaning over too far, says Stephen Robinovitch, a professor in the biomedical physiology and kinesiology and engineering science departments. Other, less frequent reasons for falling included loss of support with an external object, like a walker, or bumping into something.
Dr. Robinovitch says a typical test in a doctor's office of older people's balance and risk of falling might involve watching them walk around. Assessments should be more involved, because a greater risk of losing their balance is when they are shifting their weight, such as standing up and sitting down, he says. The study was published in the journal The Lancet in January.
"The environment certainly is important but by and large intrinsic causes of imbalance dominate over extrinsic," Dr. Robinovitch says.
Source: The Wall Street Journal