Study reveals how fatigue affects Soldiers

Tuesday, June 3, 2014 - 6:00pm

A new collaborative study at Natick Soldier Research, Development and Engineering Center looks at biomechanics and cognitive responses simultaneously to help determine how fatigue affects both the mind and body of Soldiers.

Researchers at Natick Soldier Research, Development and Engineering Center, known as NSRDEC, are testing Soldiers as they complete a prolonged march while carrying a load totaling 88 pounds. The Army is developing future predictive models of Soldier performance, including load carriage.

"What we are striving to do with our current research is to identify the biomechanical markers at the onset of fatigue and supply data for validation purposes to analyze what happens to the Soldier over time during prolonged marching tasks," said Dr. Leif Hasselquist, NSRDEC biomechanist. "In addition to the collection of biomechanical and physiologic data, we're administering cognitive tests that will allow us to evaluate both the biomechanical and cognitive changes that occur over time during a march. This research is unique in that we are combining our traditional biomechanical tests with dynamic cognitive tests. This hasn't really been done before -- especially with Soldiers."

Every Soldier's peak VO2 -- maximal oxygen intake -- is measured and used as a measure of his or her fitness level. During the studies, Soldiers are pushed past 50 percent of their peak VO2. This is the level of exertion used in this research to define the onset of fatigue for Soldiers.

Biomechanical and cognitive measures are analyzed to reveal how the Soldiers are changing their gaits and cognitive functions as they continue to fatigue. The first phase of testing, completed last year, involved Soldiers marching on a treadmill for a two-hour march, or six miles, at a four-percent grade uphill.

While continuing to analyze data from the first phase of the study, Hasselquist said that "our goals of achieving the onset of fatigue were met. During that second hour, we see a creeping up in the energy cost over the 50 percent peak VO2 levels."

The second phase, currently ongoing, looks at recovery from fatigue. The Soldiers march uphill for one hour and then either descend at an eight-percent grade during one condition or march at varied grades during the second hour (uphill four percent, level and downhill eight percent).

NSRDEC's biomechanics lab has unique motion-capture system and integrated force plate treadmills that allow scientists to record this data from Soldiers during prolonged load carriage. The lab can capture biomechanics and physiologic measures in a synchronized fashion.

"I like to say that Soldiers are like athletes," Hasselquist said, "except athletes perform and they're done. Soldiers have to do a six-to-12-mile road march and get in there, and then they have to perform, so you want them optimized. If we can find strategies to mitigate or predict how fatigue from load carriage affects the Soldier, our research will be helpful."

Cognitive testing ranged from simple to complex tasks that looked at different brain functions throughout the march. During one test, Soldiers received audio cues of either AK-47 or M-4 fire. They then had to differentiate friendly fire from opposition fire and respond through a trigger switch on their weapons.

A visual task using state-of-the-art eye-tracking glasses monitored Soldiers' eye movements as they scanned environments for targets on TV screens. At detection of pop-up targets, the Soldier was required to respond as quickly as possible though the trigger switch. Response time and whether or not they were making the right choices were recorded.

"This is a synchronized evaluation of the Soldier in the biomechanics lab," Hasselquist said. "It's a complete look at the Soldier, not just one segment, one task or one response at a time. You get the whole picture of what's going on with the Soldier."

Markers are placed on Soldiers' bodies, as in the video gaming industry, to build physics-based models of Soldiers through the motion-capture software. Electromyography, or EMG, is also used and measures the muscle activity from the Soldiers' muscles. Researchers are able to detect the intensity and fatigue in the leg muscles over time, and the cognitive responses during the march are overlaid on top of these results.

In the past, researchers looked at biomechanical, physiologic and cognitive studies separately. Now, NSRDEC's study brings those key pieces together to improve the understanding of the science behind the Soldier as all of the data is captured simultaneously.

Information acquired in this study is critical for accurate representation of the capabilities and limitations of the dismounted warfighter in Soldier models and simulations. The data acquired will result in recommendations regarding existing and future load carriage strategies, route-planning tools, Soldier performance expectations, and improvements in designs of future load-carrying equipment.

It is the goal of the NSRDEC researchers to apply the current research strategies to a third phase of research. New technology in biomechanical sensors and cognitive measures will allow the Soldier's biomechanics, physiology and cognitive responses to be captured outside the laboratory during field exercises.

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Natick Soldier Research, Development and Engineering Center is part of the U.S. Army Research, Development and Engineering Command, which has the mission to develop technology and engineering solutions for America's Soldiers.

RDECOM is a major subordinate command of the U.S. Army Materiel Command. AMC is the Army's premier provider of materiel readiness -- technology, acquisition support, materiel development, logistics power projection, and sustainment -- to the total force, across the spectrum of joint military operations. If a Soldier shoots it, drives it, flies it, wears it, eats it or communicates with it, AMC provides it   

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