Filed under: Environment
Walk into any fitness center on base or take note of a group of soldiers training, and you’ll probably notice at least a few people in form-fitting synthetic t-shirts. The sports apparel industry has exploded in popularity over the past decade, with numerous manufacturers now competing to develop, market, and sell the newest pieces of clothing (shirts, shorts, underwear, socks), all geared to keep athletes cool while competing or training in hot environments. Is there any science behind these claims? Does tight-fitting clothing made of “high-tech” materials actually help with heat regulation and enhance athletic performance?
You heat up when you exercise, and sweating is the primary method your body uses to stay cool. Sweat evaporating off your skin is the most important method your body has to cool itself during exercise. High-tech materials are supposed to enhance “wicking”—the delivery of sweat away from the skin surface toward the clothing, which allows for evaporation—and limit the absorption of sweat by the clothing itself. Cotton, by contrast, absorbs moisture, so it’s not considered a good choice for exercise.
To date, there’s no evidence that this high-tech clothing improves thermoregulation when worn during exercise in hot environments. Specifically, researchers found no differences in heart rate or body and skin temperatures when subjects performed repeated 20–30 minute bouts of running outfitted in shorts, sneakers, and either a form-fitting compression or traditional cotton t-shirt. Research has also found that wicking sportswear had no effect on cooling when worn under a bulletproof vest or on a cycling sprint when worn under full ice hockey protective equipment. As of now, the best advice for staying cool during exercise in the heat is to wear lightweight clothing, stay properly hydrated, and listen to your body for signs of potential heat illness. For more information on performing in hot environments, please visit the “Heat” section of HPRC’s Environment domain.
Performing physical activity—whether exercise or mission demands—at moderate (4,000–7,900 ft or 1,200–2,400 m) and high (7,900–13,000 ft or 2,400–4,000 m) altitudes can be challenging. At high altitude, oxygen pressure is lower, which results in less oxygen in the blood and muscle tissues. And as altitude increases, there’s a decrease in air temperature (about 2°F for every 500 ft or 150 m), less moisture (resulting in drier air), and increased solar radiation. Use sunscreen, drink plenty of water, and watch out for the signs of acute mountain sickness: headache, nausea, shortness of breath, and impaired cognition and balance.
To learn more about altitude sickness, read the article “The Invisible Enemy of the Afghanistan Mountains” on the United States Army Research Institute of Environmental Medicine (USARIEM) website. And learn more about performance at altitude in the Altitude section of HPRC's Environment domain.
With current and future military operations in mountainous regions, the issue of acute mountain sickness (AMS) is a significant medical concern. AMS can affect anyone, military or civilian, who is unacclimatized and/or ascends too rapidly to high altitudes. Symptoms of AMS can include headache, nausea, fatigue, dizziness, and sleep disturbances. Recently, researchers at USARIEM were able to predict the severity and prevalence of AMS after rapid ascent to various altitudes. What they found was that for every thousand-meter increase in elevation over 2,000 m, a person was over four times more likely to develop AMS. In addition, the severity of sickness doubled, and the odds that the AMS would worsen increased almost five-fold. AMS appeared to peak at 18 to 22 hours of exposure to altitude and then went away after 42 to 48 hours. The severity of sickness is greatest above 4,000 meters and may require evacuation to lower altitude or immediate medical attention. It also appears that men are more likely than women to get AMS and more likely for it to be severe. For both men and women, the more active they were at altitude, the longer it took to recover. These findings support current recommendation to limit activity as much as possible in the first 24 hours at altitude to decrease the risk for AMS.
This information should help military leaders manage and perhaps prevent AMS among troops by knowing the elevation, types of activities, and lengths of stay at altitudes.
In order to reduce the risk for AMS, acclimate to moderate elevations (2,000 – 3,000 m) if/when possible. In addition, stay hydrated and try to limit your physical activity at altitude for the first 24 hours. Read more about the effects of altitude on performance and how to minimize your risk for AMS.
Giant hogweed—no, it’s not an ingredient in one of Harry Potter’s potions; it’s a large poisonous plant that started to bloom in the northeast and northwest areas of the U.S. and parts of Canada earlier this month. If you’re out for a ruck march through the woods and you come across this plant, do not touch it. The sap can cause irritation and burns to your skin and perhaps blindness if it gets into your eyes. If you do happen to come in contact with it, be sure to wash your skin with soap and water and keep the area out of the sunlight for 48 hours. Giant hogweed can grow 14 feet or higher. It’s characterized by large leaves and white, umbrella-shaped flower clusters at the top of the plant. It may be difficult to distinguish from other non-poisonous plants such as cow parsnip, so err on the side of safety if you’re not sure. You can read more about identifying invasive species in your area from the U.S. Department of Agriculture.
Your sunscreen has an expiration date—have you checked it lately? It’s meant to last up to about three years; after that, the active ingredients start to deteriorate, making it less effective and leaving you vulnerable to sunburn and sun damage. Ideally, you should be using your sunscreen often enough that a bottle doesn’t last through the summer. If that’s not the case, check the bottle you’re currently using—if it’s old, throw it out. If you buy sunscreen that has the expiration printed only on the box or wrapper, write the date somewhere on the bottle itself with a permanent marker. Practice safe sun this summer to keep you and your family healthy and happy!
Lyme disease is a serious concern for those who spend a lot of time in heavily wooded areas and a especially for the DoD. It’s common in the United States and around the world and is caught from the bite of two different species of ticks—the deer tick and the western blacklegged tick.
After spending time in wooded or grassy areas, check yourself all over, including your back (enlist a friend or a mirror to help). The early removal of a tick that’s attached to you is key in preventing Lyme, since the tick must be attached for 24-48 hours in order to transmit the bacteria that cause this disease. Ohio State University conducted a study using different tick-removal tools and concluded that all three tools were effective—and confirmed that early removal is more important than the type of tool that is used. The Centers for Disease Control provides easy-to-follow tips on tick removal using just tweezers.
If you know you’ve been bitten by a tick, or begin to notice symptoms such as a bullseye rash (an early sign of Lyme infection) at a bite location, fatigue, chills, fever, muscle aches, or swollen lymph nodes, you should to see your doctor. Blood tests can be used to confirm whether the symptoms are from Lyme disease. If left untreated, more severe symptoms can occur, such as loss of muscle tone in the face (called Bell’s palsy), severe or shooting pain, and heart palpitations. A typical successful treatment includes a course of antibiotics, but there can still be lingering symptoms, called chronic or post-treatment Lyme disease syndrome. When it comes to Lyme disease, the best offense is a good defense. Some tips for prevention:
- Wear your military uniform properly. This can help to prevent tick bites since long pants, long sleeves, and pants that are tucked into boots minimize exposed skin.
- Use insect repellents such as DEET or Permethrin.
- If you are in a wooded area, avoid tall grasses and brush. If this isn’t possible then be sure to follow tips #4–7 below as you are able.
- Perform a thorough skin check—especially of the hair and base of the skull at the hairline.
- Shower within two hours of being outside. This can help wash off ticks that are still crawling on the skin.
- Examine gear and pets for hitchhiking ticks.
- If you have access to a dryer, put your clothes in it for an hour on high heat to kill any ticks.
If you are interested in more information on diseases and conditions that are spread by ticks, insects, or other pests, you can visit the Armed Forces Pest Management Board.
Warfighters involved in Operation Desert Storm to current missions in Iraq and Afghanistan may be experiencing what the Institute of Medicine is calling “Chronic Multisymptom Illness.” Research suggests that it is connected to toxins and contaminated environments in Middle East combat zones. Those who appear to be suffering from it have apparently unexplainable symptoms lasting at least six months in two or more of the following categories: fatigue, mood and cognition issues, musculoskeletal problems, gastrointestinal problems, respiratory difficulties, and neurologic issues. Dust storms and smoke from burn pits may be the vehicles for transporting toxic metals, bacteria, viruses, and perhaps the nerve gas sarin. Experts suggest that high temperatures and low humidity in the Middle East cause people to breathe more through their mouths than through their nose, carrying the pollutants deeper into the lungs, especially during rigorous physical activity. New legislation has recently set up burn pit registries to track the medical histories of those who may have been exposed to smoke from the practice of burning waste (human, plastic bottles, etc.) using jet fuel. With the rise of unexplained medical conditions among younger veterans of recent conflicts, researchers are looking for more conclusive evidence as to what exactly is causing this chronic illness. In the meantime, the IOM has just published a report with extensive information and recommendations for treatment.
It’s important to get enough water, especially when it’s hot. However, too much water can lead to a dangerous condition known as hyponatremia in which the sodium levels in your blood drop too low. It’s often caused by drinking too much water and is common among military personnel, athletes, and hikers. Significant weight gain (due to fluid retention) during exercise can occur, along with longer finish times for endurance activities. If you have a Body Mass Index (BMI) below 20, you are more likely to develop this condition. For more in-depth information, read HPRC’s InfoReveal on over-hydration.
Sweat is a critical function when you’re performing in hot environments. As your body absorbs heat from the environment, your nervous system activates sweat glands to release sweat. The moisture on your skin then evaporates, taking heat away from your body and cooling you off.
Protective clothing impedes the evaporation of sweat and the heat exchange between you and the environment, a condition known as “evaporative resistance.” This means that the exposed parts of your body will cool off more quickly than the parts that are covered, but they are also more prone to insect bites. Reports from Marines and National Park employees feeling “excessive heat” and a loss of sweating sensations after applying moderate to high amounts of DEET to their skin brought the safety of this insect repellent into question.
In a recent study, researchers found that when 33% DEET lotion is applied according to military protocol, it does not interfere with sweat production or other physiological responses. Nor does it interfere with the evaporation process necessary for cooling to take place. Researchers concluded that 33% DEET can be worn safely during military and occupational activities performed in hot, insect-infested environments. Similar studies have found oil- or alcohol-based repellents may increase core temperature by reducing sweat evaporation rate but do not affect sweat production. The military-approved form of DEET is polymer-based.
You can watch a YouTube video about the science behind the study.
DEET is considered by the EPA to be a toxic pesticide. It should be used with caution and as directed. More information about DEET, its uses, and warnings can be found on the EPA fact sheet. As of 2004, DEET was considered safe for use on children older than two months of age. Specific information on its use and effect on children can be found in the EPA TEACH chemical summary.
Pentagon scientists are hoping to build special gear designed to turn divers into veritable Aquamen (and Aquawomen). Although it’s still in the research phase, the new system would protect divers from the adverse effects of diving too deep or surfacing too fast. Sensors would read and adjust to a diver’s physical signs as well as help control levels of nitric oxide to prevent the decompression sickness known as “the bends.” When a diver ascends too quickly, bubbles form inside the body, which can block the blood vessels in the spinal cord and disrupt the nervous system. It can be very painful and can lead to joint pain, paralysis, and even sudden death if a diver is not careful.
The new diving gear will be a portable and versatile system that can potentially serve for use in other special operations as well as for civilian divers. This system will have to be designed for the most extreme combat dive profiles, which sometimes require a 35,000-meter free-fall from an aircraft, diving 200 feet below the surface for at least two hours, surfacing, and immediately diving again, followed by continued protection after being picked up in an unpressurized aircraft. This is one of DARPA’s most recent Small Business Innovation research proposals for 2013.