Anyone preparing for a long-distance hike is familiar with this dilemma: how much water do you bring? If you don't pack enough, you risk dehydration; if you pack too much, you're stuck carrying it. It's even harder to estimate water needs in higher altitudes, as they can vary substantially.

It's particularly important for soldiers in the field to be able to estimate their water needs in advance. For soldiers in the field, water is logistically burdensome to transport, but important to health and performance. That's why U.S. Army researchers successfully developed, tested, and validated an equation to help predict the amount of water needed.

During the validation phase of the research project, they used Adam Equipment's CPWplus scales in a study to analyze the sweat rates of a group of hikers climbing Mt. Kilimanjaro in Tanzania.

The CPWplus offers several key features that were essential for this study, according to Robert Kenefick, Ph.D., research physiologist in the Thermal and Mountain Medicine Division (TMMD) at the U.S. Army Research Institute of Environmental Medicine in Natick, Mass.

Researchers knew they'd have to carry the scales in their backpacks during the journey. That meant the scales had to be lightweight and also fit in backpacks. Battery operation was necessary, since electricity is unavailable, according to Kenefick, who served as one of the project study leaders. The CPWplus was the perfect solution.

"We bought the scales because they fit our need to be portable and precise for the study," Kenefick said. "The CPWplus was easy to operate and speedy, which facilitated the weighing process of the volunteer hikers during the study," he said.

The group comprised 22 men and women from the New York City Explorers Club, who were participants of a flag expedition. They followed the popular Lemosho Route, which is one of the most scenic routes up Mt. Kilimanjaro. From the starting point at Rain Forest Base Camp (2,829m) to the final stop at Shira Camp (3,505m), the route offers an ascent rate of 350-1,500m daily, which was ideal for the project.

During treks, Kenefick determined individual sweat rates by recording each hiker's nude weight, and by tracking food and fluid intake and urine output. To ensure privacy, Kenefick pitched a small tent and set up the CPWplus scales inside.

Sweat-rate calculations were based on individualized metabolism and clothing, along with environmental factors such as sun, temperature, relative humidity and barometric pressure.

The human body loses water in different ways, such as perspiration, respiration, urination, defecation. Perspiration, or sweating, contributes to the greatest water loss during exertion at high altitudes, probably as a result of lower humidity, which promotes the evaporation of water from the skin. At high altitudes, even moderate water loss can cause physical problems, including impaired aerobic performance and increased symptoms of acute mountain sickness, which can be debilitating.

The study was the first to provide sweat rate measurement information for high-altitude, outdoor activities. Results validated the researchers' equation, which gave them a way to accurately predict an individual's water needs during exertion at higher altitudes.

Kenefick said the CPWplus scales have also been used during other TMMD lab and field research projects, including a study of acute mountain sickness, which was conducted at USARIEM's Maher Memorial Altitude Laboratory on Pikes Peak in Colorado. Projects such as these help researchers learn more about how the human body reacts and adjusts to changes in altitude.

During this study, Kenefick and other investigators used the CPWplus scales while monitoring study participants at various altitudes, to learn about the impacts of acute mountain sickness and exercise performance.

For more information on the CPWplus, visit

For information on the USARIEM Thermal and Mountain Medicine Division, visit