Clinical Topics

Researcher’s Focus on Walking Helps Improve Health, Safety of Veterans

by Stephen Spotswood

September 20, 2019

David Clark, ScD

GAINESVILLE, FL—When people want to describe themselves as uncoordinated, they might say they have trouble walking and chewing gum at the same time. However, the act of walking—one of the most basic human skills—is not nearly as simple as that phrase makes it sound.

David Clark, ScD, a researcher at the Brain Rehabilitation Research Center at the Malcom Randall VAMC in Gainesville, FL, stresses that walking is not a single task but rather a complex series of neurological events that can become more difficult as a person ages.

“If you think about your legs, there are several joints that can move in many different directions. There are dozens of muscles. And your nervous system doesn’t have to think about which muscle to contract and what joint to move. All of these complex motions are done automatically,” Clark explained. “We have circuits in our nervous system that take care of that complexity. They produce those patterns of muscle activation for us, so we don’t have to think about it. What happens when people get older or when people have a neurological injury, like a stroke—that automaticity of movement is impaired.”

Source for graphic: David Clarke included this graphic in an article: Front. Hum. Neurosci., 05 May 2015 | https://doi.org/10.3389/fnhum.2015.00246 (Click on image to enlarge)

With a background in exercise physiology and a doctorate in rehabilitation sciences, Clark has devoted his career to understanding how the nervous system adapts to rehabilitation and how therapy can be improved so that walking-impaired veterans can lead safer, healthier lives.

Cognitive Task

“I don’t think people realize that walking becomes a cognitive task as people get older. It becomes taxing on your brain to think about how to control your movement, and it makes people more susceptible to falling. That’s why we care about it. We don’t want people to fall and get hurt,” Clark explained.

Like in many research endeavors, the first challenge has been figuring out how to measure impairment and improvement.

“One of the main things is understanding how to measure restoring control. How do we measure whether someone has more automatic control or whether walking is more cognitively demanding?” Clark asked.

The answer he and his fellow BRRC researchers have hit upon is functional near-infrared spectroscopy. By measuring changes in near-infrared light, it allows them to monitor blood flow to the front part of the brain. “It’s sort of a headband we have people wear that has technology in it that lets us measure how active their brain is while they’re walking,” Clark explained.

His other major research goal is to improve rehabilitation for patients who are having difficulty walking. One of Clark’s projects involves physical therapy patients being provided noninvasive, mild electrical stimulation to the brain using electrodes attached to their forehead. Previous studies have shown this method could be effective in helping reinvigorate the neural circuits responsible for controlling the many different elements of walking. However, this is the first study using the intervention across multiple sessions.

In a similar study, Clark is moving the electrodes from the forehead to the lower back in an attempt to stimulate the lumbar spinal cord. “The spinal cord is where a lot of these neural circuits are—the central pattern generators that we think create the pattern of muscle coordination needed for walking,” he explained. “We’re trying to use this electrical stimulation to upregulate those circuits.”

Because of the sheer number of variables in these studies, Clark expects to be working on them for the foreseeable future, tweaking different elements to narrow in on the best protocol. “Currently patients in the study are stimulated for 20 minutes using two milliamps of current. We don’t know if those are the right parameters,” Clark explained. “In terms of where we place the electrodes, we don’t know if we have that quite right. Is 16 sessions too little or too much? Maybe 80% of improvement happens in the first 10 sessions.”

Thinking of the field as a whole, Clark said that personalized medicine will have a big impact on rehabilitation. Not all gait impairments are the same, so not all therapy can be the same.

“People spend a lot of time in physical therapy,” he said. “And if you’re not doing the right therapy, that’s a lost opportunity.”

Clark noted that, while the attention of the nation has naturally turned toward the most recent generation of veterans, the previous generations are continuing their path to old age and the ailments that come with it. That makes research into age-related impairment more important than ever for VA. 

“About half of veterans are 65 and older,” he said. “Loss of mobility function and loss of independence is a huge cost and a huge issue that the VA healthcare system is going to be dealing with for decades to come.”



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