Dr. Shirley Handelsaltz of Ben-Gurion University is researching how people who have had a stroke control the natural variability of walking, and why subtle disruptions in this control may increase the risk of falls.
When we walk, our steps are not the same. Even in a healthy person, the length of the step, the duration of the step, and the movement of the joints vary slightly from step to step. This variation is not a malfunction. It allows us to adapt our movement to a changing world: an uneven sidewalk, an obstacle in the way, a dog pulling on a leash, or a sudden disturbance of balance.
But after a stroke, this control of variability can go awry. Many people manage to walk again, but their gait is not necessarily stable, efficient or safe. The question that concerns Dr. Shirley Handelsaltz, of the Department of Physiotherapy at Ben-Gurion University of the Negev, is not just whether a person who has had a stroke can walk, but how they walk. “We test people who can walk,” she explains, “but their gait is simply not good enough. They may be able to walk down a long hallway on a flat floor, but have difficulty walking steadily in a more complex environment, which can lead to a fall.”
The question is: How can the risk of falls be reduced in stroke patients?
When oxygen doesn't reach the brain
A stroke occurs when brain tissue is damaged by a blocked blood vessel or bleeding. An area of the brain that is deprived of oxygen can lose function, and rehabilitation attempts to harness the brain's plasticity, its ability to reorganize, so that undamaged areas can help restore function. Sometimes even minor damage to an area where important motor pathways pass can cause severe movement impairment.
Handelsaltz’s research, supported by the National Science Foundation, is concerned with the brain’s ability to use the many movement options available to it during walking. The human body has more joints, muscles, and movement options than are ostensibly required to place the foot in a particular place. The brain needs to limit, or reduce, the variation in the components that are important to the outcome, such as where the foot lands, but allow for variation in other components that do not compromise the goal and even allow for flexibility and correction. “As a physical therapist, I am not trying to reduce all variation in movement,” says Handelsaltz. “We need to understand which variation we want to reduce, and which variation actually allows for adaptation.”
Sometimes even minor damage in an area where important motor routes pass can cause serious disruption to traffic.
Walking in changing conditions
The research is being conducted in the gait rehabilitation laboratory at the Levinstein Rehabilitation Medical Center in Ra’anana. The patients walk on a computerized treadmill, surrounded by cameras for 3D motion analysis, and markers are attached to their bodies that the system tracks. This allows an accurate model of body movement to be built and the variability in each joint and each step to be measured. The system samples the movement at a rate of 120 images per second.
The subjects don't just walk under normal walking conditions. The study also tests them walking on narrow paths, and in situations where the treadmill suddenly moves sideways or forwards and backwards. These are unexpected perturbations, designed to test how the subject reacts when their balance is disrupted. The subjects are secured in a harness, but are required to change their stride or body movement so as not to lose stability while walking.
Initial results indicate that in people after stroke, both components of variability are high: both the variability that affects the accuracy of foot placement, and the variability that is not supposed to directly affect the outcome. In other words, the problem is not just “imprecise walking,” but probably a more subtle impairment in the control mechanism that governs the variability in joint movement during walking.
Another part of the study examines the relationship between the nature of walking and the location of brain damage. To do this, the researchers use structural brain imaging, MRI, mark the areas of damage, and compare patients with damage in certain areas with patients without damage in those areas. The goal is to understand whether damage to a particular brain area is associated with difficulty controlling variability while walking.
The final part of the study will examine whether walking training in a challenging environment changes the ability to control variation in people who have had a stroke.
Ultimately, poor gait can lead to falls, and falls are not a minor event. They can cause injuries, fractures, decreased function, fear of movement, isolation at home, and significant damage to quality of life. Handelsaltz's research seeks not only to improve walking in laboratory conditions, but to restore the ability of people after a stroke to move around the world with greater confidence.
Short FAQ:
Why is gait variability not necessarily a problem?
Even in a healthy person, steps are not the same. A certain variation allows walking to be adjusted to uneven pavement, obstacles, and sudden disturbances in balance.
What goes wrong after a stroke?
Some people who have had a stroke have impaired control over their movement. They can walk, but their walking may be less stable and less safe in complex environments.
What does the study examine?
The study examines how people after a stroke respond to walking under varying conditions, including narrow paths and sudden interruptions of the treadmill, as well as whether the location of the brain injury is related to difficulty in controlling gait.
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