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Risks of activity at altitude

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Altitude affects what your body needs and how it responds, especially when it comes to exercise.

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.

Predicting acute mountain sickness

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Scientists suggest how likely you are to experience altitude sickness while at elevation.

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.

Mask you a question?

HPRC Fitness Arena: Environment, Total Force Fitness
Are you using your military Pro Mask correctly? Wearing your mask during exercise won’t prepare you for performing at altitudes, but increasing your respiratory muscle strength certainly has benefits for your performance.

Increasing the strength of your respiratory muscles (the ones that help you breathe: your diaphragm and the muscles between your ribs) will improve aerobic fitness, especially for long-duration tasks. Respiratory muscle training (RMT) can be achieved through whole-body aerobic exercise, upper-body strength conditioning, and some commercial RMT devices. However, using your military Pro Mask or other commercial mask device as a method of RMT is not going to prepare you for higher elevations. Studies have also found that RMT only slightly improves performance in those who are already aerobically fit, (i.e., military personnel); it has somewhat more benefit for those less fit or with chronic conditions. Your Pro Mask was made to protect your lungs, eyes, and face from chemical and biological agents, radioactive particles, and battlefield contaminants. It does not create enough airflow resistance to help improve aerobic capacity, and it wasn’t designed to be exercise equipment. In addition, there is no scientific evidence to show that using commercial masks at normal altitudes will improve your performance at high altitudes. You can read more from USARIEM about using Pro Masks and commercial products for exercise training, as well an overview of current information and recommendations.

F-22 jets under fire

HPRC Fitness Arena: Environment, Total Force Fitness
On September 13, Air Force officials met on Capitol Hill to address the House Armed Services Committee over concerns about the physiological dangers of flying F-22s.

Why has the F-22 Raptor been depriving its pilots of oxygen for the last 12 years? Air Force officials recently told a House subcommittee hearing (a complete video of the two-hour hearing is also available) that they don’t know what’s behind the dizziness, confusion, blackouts, memory loss, fatigue, and eventually chronic cough (“Raptor cough”) that pilots experience while flying the stealth jets. After more than a dozen incidents between 2000 and 2011—and one fatal crash—where pilots were being choked by the plane, the Air Force’s entire F-22 fleet was grounded in May 2011.

Investigations ruled out low blood sugar and dehydration as possible causes of the symptoms and eventually concluded that the problem was an overinflated pressure vest that restricted breathing.

In response, a team of NASA engineers and Navy divers developed a new-and-improved pressure suit and back-up oxygen systems and removed a faulty charcoal air filter. These measures seem to have alleviated the problems—a dozen F-22s recently were deployed to Japan without incident. Now restrictions are being lifted, although the jets and their pilots are being closely monitored. Pilots currently must operate under altitude ceilings so that they don’t need to use the flight vests, and they must also stay close to emergency landing sites. Experts and scientists continue to investigate the primary cause of these incidents as well as improve safety and back-up systems.

Overcoming jet lag without medications

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Jet lag can be a drag to get over, but you can prepare yourself with some simple actions to help you deal with this common annoyance.

If you’ve ever switched times zones, even as little as one hour, you may be aware that it can disturb your sleep and even disorient you in the following days. Without taking any medicinal countermeasures, you can typically adapt to your new time zone with about one hour of extra sleep per day after arrival (depending on with direction you’re traveling). However, some operations require that you be able to perform within 24 hours of arrival. To better prepare and adjust to your new time zone, use these strategies:

  • One week before you travel, adjust your sleep schedule about one hour per night towards the time zone you are flying in—i.e., if flying eastward, go to bed and get up earlier; if flying westward, sleep later.
  • Before you take off and while on the aircraft, eat light snacks, avoid alcohol, and stay hydrated (with water).
  • On the aircraft, make sure that you are comfortable and able to nap before you arrive at your destination.
  • Setting your watch to your new time zone as soon as you board your flight will help you transition.
  • Take a short nap when you arrive at your new location, if you’re able to do so.

For more information, read the sections on jet lag in this article on sleep rhythms.

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