The way people walk appears to speak volumes about the way they think, so much so that changes in an older person's gait appear to be an early indicator of cognitive impairment, including Alzheimer's disease.
Five studies presented at the Alzheimer's Association International Conference in Vancouver this month provide striking evidence that when a person's walk gets slower or becomes more variable or less controlled, his cognitive function is also suffering.
Thinking skills like memory, planning activities or processing information decline almost in parallel with the ability to walk fluidly, these studies show.
In other words, the more trouble people have walking, the more trouble they have thinking.
"Changes in walking may predate actually observable cognitive changes in people who are on their way to developing dementia," said Molly Wagster, chief of the National Institute on Aging's behavioral and systems neuroscience branch. Experts said the studies could lead to developing a relatively simple tool that doctors could use to forecast, if not diagnose, possible Alzheimer's disease.
"You can probably just watch them walk down the hall in your office and look for people who are starting to show deterioration in their gait and have no other explanation for it," said William Thies, the chief medical and scientific officer for the Alzheimer's Association. "If gait begins to deteriorate, we begin to have a conversation about how is your memory."
While scientists have studied gait changes after a heart attack or stroke and in diseases like Parkinson's, they have only recently begun studying connections between walking and cognition. For decades, people thought slower walking was just part of getting old, but research shows some changes in gait signify problems that go beyond normal aging.
"It's like driving a car - you need an engine, a chassis and steering," said Dr. Stephanie Studenski, an expert on walking who was not involved in the dementia studies. The engine of walking is the heart, lungs and blood, she said. The chassis is the muscles, joints and bones.
And the steering is "the wiring - the nervous system," said Dr. Studenski, a geriatrician at the University of Pittsburgh and the Pittsburgh Veterans Administration.
"People who are focused on cognition largely never watch people move," Dr. Studenski said. "The tests are all done sitting down. But damage to the wiring is an important shared problem of difficulty with thinking and difficulty with moving."
The new studies were larger and more detailed than previous research, and involved sophisticated measures of changes in gait. Some used an electronic walkway, a long mat outfitted with sensors that measure small differences in walking speed, cadence (the number of steps per minute), the width of the stride and variability (how often the person's stride changes).
The studies screened out people with arthritis or other physical problems, and adjusted for height, age, weight and sex.
One study involved more than 1,100 elderly people in Basel, Switzerland. About a quarter of them were cognitively healthy, while the others had mild cognitive impairment, considered a precursor to dementia, or were in various stages of Alzheimer's.
The participants walked normally on the electronic walkway, and again while performing a cognitive task: counting backward by two's from 50, or naming animals.
One 72-year-old woman's first walking test betrayed no problems. But when she walked while counting backward from 50, her gait worsened dramatically, said Dr. Stephanie Bridenbaugh, head of the Basel Mobility Center.
"She teetered and wobbled on one foot," Dr. Bridenbaugh said. "She almost tipped to the side." And "she didn't notice any of it," she added. "She was mad that she didn't remember more numbers."
Dr. Bridenbaugh referred her to the memory clinic, where cognitive testing showed the woman already had mild cognitive impairment.
Asking people to simultaneously perform thinking and movement tasks revealed "deficits that you can't see with the naked eye," Dr. Bridenbaugh said. It may be that the brain is already so compromised that it cannot coordinate its circuits to efficiently manage such "dual tasks."
"A lot of times normal walking looked normal, even in people with moderate Alzheimer's, but if you look at dual tasking, I can detect these problems," said Dr. Bridenbaugh. Her research consistently showed that people who walked more slowly or inconsistently did worse on cognitive tests; the worst walkers had the most severe Alzheimer's.
A large study at the Mayo Clinic involved basic walking, not dual-tasking, but found a similar relationship, said Dr. Rodolfo Savica, a neurologist at the clinic. Most of the 1,341 participants did not have dementia. They were evaluated twice, 15 months apart, with tests of cognitive ability and walking.
Dr. Savica and his colleagues found that on average a person who walked one meter per second slower on their second test scored half a point lower on cognitive tests.
Slower walking was mostly strongly linked to declines in "executive function," the ability to plan and organize activities. A study led by Dr. M. Arfan Ikram, a neuroepidemiologist at Erasmus MC University Medical Center in Rotterdam, tried to connect particular changes in gait with specific cognitive impairments.
More than 1,200 people with no signs of dementia were asked to walk normally, to walk and turn around halfway through, and to "tandem walk," in which the heel of one foot is placed directly in front of the toe of the previous foot. The subjects also were given cognitive tests.
People with poor tandem walking scored low on tests involving fine motor skills. People with lower cadences, who took fewer steps per minute, did worse on tests of thinking speed. And people whose walks were slower and more variable showed poor executive function.
Dr. Ikram said no specific aspect of walking was correlated to memory problems, perhaps suggesting "that memory is purely a brain function which expresses itself only in cognition."
Aside from suggesting that walking may provide early clues that dementia is on its way, the studies may reinforce the possibility that physical activity could help stave off dementia. If slower and more erratic walking signifies neurological damage, could exercises to improve fitness and coordination not only help people walk, but also by help them think?
"Those are the ultimate questions," Dr. Ikram said. "Right now, we are really at the first step."
Next, said Dr. Bridenbaugh, "what we need is to use the information we have here and find a screening tool that physical therapists and doctors can use to red flag those who have a mobility problem. This should be basic. When your patient is in your office and you listen to their heart, it should be basic to see how they walk."