Filed under: Altitude
Can you train in the heat to improve your performance at altitude? The answer is “sort of.” “Cross acclimation” or “cross tolerance” is the idea that exposing yourself to one environmental condition can help you adapt to another one as long as they have certain things in common.
As it turns out, this is the case for heat and hypoxia (low oxygen). This is important because athletes and service members can be exposed to altitude without prior or sufficient acclimatization. Altitude sickness can cause several problems, especially decreased performance. But some evidence shows that this method of training in hot conditions to prepare for altitude can actually work.
If you climb to the top of a mountain, there’s less air and less pressure. And you’re getting less oxygen with each breath. This can be simulated at sea level (in special labs) where pressures are normal, but the amount of oxygen in the air is reduced (fake altitude).
However, there’s a bit of a catch. Training in the heat under artificial low-oxygen conditions—normobaric hypoxia or “fake altitude”—involves normal pressure, which is different from “real altitude” or hypobaric hypoxia, which involves reduced oxygen at low pressure. The difference is in the pressure.
So, do these two environments cause the same types of physiological changes? There are several other factors involved in real-altitude acclimatization that might not be accounted for at fake altitude, so the jury’s still out.
Training in the heat might prepare you for performance at altitude—to a point. Ideally, if you’re going to be at altitude, try to acclimatize yourself as much as you can.
The Altitude Readiness Management System (ARMS) app’s designed to predict how likely Soldiers are to experience acute mountain sickness and decreased physical performance at various altitudes. Using this new Android app (developed by the U.S Army Research Institute of Environmental Medicine), leaders can plan mountain missions around those likely to be impacted by sickness.
The ARMS app also provides an acclimatization module for planning strategic ascents and rests to minimize sickness. Altitude sickness can cause serious symptoms including nausea, fatigue, headaches, and weakness, affecting health and the mission itself too. While the app can’t prevent illness, it can help minimize the impact of mountain sickness, set appropriate expectations, and improve readiness and performance. The app has been fielded to the U.S. Army Forces Command (FORSCOM) and the U.S. Special Operations Command (SOCOM) only, but it might be available to the public soon.
Using your military Pro Mask or other commercial mask device as a method of respiratory muscle training (RMT) isn’t going to prepare you for higher elevations. Increasing the strength of your respiratory muscles which help you breathe—your diaphragm and the muscles between your ribs—will improve aerobic fitness, especially for long-duration tasks.
RMT can be achieved through whole-body aerobic exercise, upper-body strength conditioning, and some commercial RMT devices. Studies show that RMT slightly improves performance in those who are already aerobically fit (e.g., military personnel). It offers 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 doesn’t create enough airflow resistance to help improve aerobic capacity. In addition, it wasn’t designed as exercise equipment. There is no scientific evidence that suggests using commercial masks at normal altitudes will improve your performance at high altitudes. Read more about the U.S. Army Research Institute of Environmental Medicine’s (USARIEM) review of Pro Masks and commercial products for exercise training. Check out HPRC’s take on using high-altitude masks and improving work performance at higher elevations.
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.