NATICK, Mass. (Sept. 17, 2018) -- Approximately ten thousand feet above sea level, in the Toiyabe National Forest in California, U.S. Army Research Institute of Environmental Medicine, or USARIEM, scientists traveled to the Marine Corps Mountain Warfare Training Center, or MCMWTC, this summer to assess energy expenditure, energy intake and physical performance in warfighters during mountain warfare training.

The MCMWTC trains U.S. service members and allied partners to fight and survive in mountainous environments during any season. Those who undergo the 30-day mountain operational training exercise at the MCMWTC learn how to conduct operations in the mountainous terrain and fight an enemy that can attack at any time in the battle space.

For Maj. Nicholas Barringer, a USARIEM research dietitian and one of the principal investigators in a team that includes Drs. James McClung and Stefan Pasiakos, it is critical that warfighters have enough fuel to operate, fight and win in such a demanding and realistic training environment.

"Training in a mountainous environment can be metabolically demanding for warfighters, especially when they are carrying heavy loads," Barringer said. "In USARIEM's previous research, we have seen that warfighters have increased energy expenditure when operating at high altitude. One reason for this, besides the increased metabolic demand of altitude, is that walking through mountainous terrain is more physically demanding than walking on flat ground."

If warfighters do not eat enough energy to match the strenuous work they perform in such demanding conditions, this could lead to "negative energy balance," Barringer added. Warfighters can experience negative energy balance for a number of reasons, such as operating in difficult environmental conditions, lack of time to prepare and consume rations, taste and functionality of rations and physical and mental stresses that can reduce appetite.

When warfighters are not eating enough required nutrients, like protein, which is necessary for recovery and preserving lean muscle mass, this can negatively impact military health and readiness. This problem has been historically prevalent in our military, and for several years, USARIEM has partnered with other U.S. and international military branches to develop solutions.

Earlier this year, Barringer and other USARIEM researchers met the MCMWTC command and medical staff, who wanted to ensure that the students were eating enough high quality food to protect their health, performance and readiness. The USARIEM researchers proposed a field study with 100 volunteers that would assess warfighters' overall energy expenditure and physiological changes during the mountain exercise.

"The purpose of this study is to determine if warfighters are consuming enough energy to meet the physical demands of mountain warfare training and if their nutritional status is linked to physical performance," Barringer said. "The study results will allow us to work with MCMWTC on developing courses of action to improve their dietary intake if necessary, whether that is as simple as increasing servings of food provided, or more complex such as working with the Combat Feeding Directorate in the Natick Soldier Research, Development and Engineering Center to produce a new ration component or meal plan. It is also important to note that the Toiyabe terrain is similar to northern Afghanistan, so there might be some lessons gleaned from this study that could apply to those battlefield scenarios."

USARIEM researchers journeyed to MCMWTC this summer to collect energy and nutrition data from a group of study volunteers for the first iteration. Researchers collected food logs and discarded rations daily in order to estimate energy intake. They also gave a subset of the warfighters doubly labeled water, which contained an isotope that allowed researchers to determine energy expenditure.

The researchers also wanted to see how the warfighters' dietary intake affected their physical performance. Researchers tested warfighters' lower body power and anaerobic and aerobic capacities by having them perform vertical jumps, a sprint test and a 20-meter shuttle run before, during and after the mountain exercise. They also collected blood samples throughout the study to assess biomarkers that indicate warfighters' nutritional statuses.

"Biomarkers help us identify other nutrition problems, so we can see where we need to intervene and provide advice, education or delivery of a new ration component or meal plan that can address MCMWTC students' needs during mountain warfare training," Barringer said.

Barringer and his research team will conduct the same study with a new set of warfighters during the MCMWTC winter mountain exercise. Barringer explained that this study iteration would allow researchers to see if the winter mountain exercise affects warfighters' energy expenditure differently than in the summer. Barringer expects warfighters' energy expenditure will be "much greater."

"Our most current study iteration allowed us to assess warfighters' nutritional intake during the summer mountain exercises, which are already physically demanding," Barringer said. "The winter mountain exercise introduces an entirely new set of obstacles for warfighters. Cold weather itself is more metabolically demanding, but when you add the extra cold weather gear and exercising through snow with a heavy load, it is even more physically demanding."

The researchers aim to present their data to MCMWTC leadership by next year.

"The MCMWTC team has been instrumental in the development and success of this project," Barringer said. "Their leadership and staff are the experts on surviving, fighting and winning in mountainous terrain. Being able to bring USARIEM's science to their Marines and potentially improve performance is exciting as we are truly executing USARIEM's mission of bringing science to the warfighter.

"The information we are gathering from this study is intended to provide warfighters with practical solutions when fighting and operating in mountainous environments. By closing that energy deficit gap, if we find one, we can ensure that warfighters are prepared to continue performing their training and missions. The lessons learned from this study will help drive recommendations and technology to improve the survivability and lethality of warfighters operating in mountainous terrain."