Field Notes
Acclimatization and Prevention

This section covers acclimatization to heat and altitude and includes advice on how to avoid two uncommon heat-related problems, hyponatremia and rhabdomyolysis.

Heat Acclimatization—It takes 5 to 10 days of heat exposure to become acclimatized: 5 days for fit workers and longer for those who are less fit. A high level of aerobic fitness increases blood volume and circulatory efficiency, both of which help the body regulate temperature. Gradually increasing work time in the heat leads to:

• Increased sweat production
• Improved blood distribution
• Decreased core and skin temperatures
• Lower working heart rate

To become acclimatized:

• Gradually increase work time, taking care to replace fluids and to rest as needed.
• Maintain acclimatization with periodic work or exercise in a hot environment.

Altitude Acclimatization—Elevations below 5,000 ft have little noticeable effect on healthy individuals. But as you ascend to higher elevations, barometric pressure declines, along with available levels of atmospheric oxygen. With less oxygen, altitude always leads to a reduction in aerobic fitness and endurance performance. It can take about 3 weeks to acclimatize to elevations between 5,000 and 9,000 ft, or about 1 week for each 1,000 ft of elevation above 5,000 ft. While athletes try to live high and train low (to maintain training intensity), workers usually live and work at the same elevation. Altitude acclimatization leads to increases in:

• Pulmonary function
• Blood volume and hemoglobin
• Numbers of red blood cells
• Numbers of lung and muscle capillaries
• Muscle myoglobin (allowing more oxygen to be transported in the muscles)

These adjustments improve the body's ability to take in, transport, and use oxygen, but they never eliminate the effects of altitude on endurance performance, including arduous work.

Hyponatremia—Sodium is available in fire camp meals, but that source of sodium may not be adequate during extremely hot weather.

To avoid hyponatremia:

• Drink carbohydrate/electrolyte (sports) beverages or put electrolytes (especially salt) in drinking water to ensure sodium intake.
  
  
• Drink half a quart of fluid (water and sports beverages) 2 to 3 hours before exertion in the heat.
  
  
• Drink a pint of fluid (water and sports beverages) 10 to 20 minuntes before exercise.
  
  
• Replace fluids lost in sweat by drinking 6 to 12 oz of fluid (water and sports beverages) every 15 to 20 minutes during exertion.

During meals, long breaks, and after exertion, replace fluids to restore fluid balance, electrolytes, and carbohydrates.

Wildland firefighters should consume a quart (liter) of fluid (water and sports beverages) for each hour of work in the heat. We recommend that firefighters use sports beverages for one-third to one-half of their fluid needs. When hyponatremia is suspected, provide electrolyte fluids, such as sports beverages–not water.

Additional carbohydrate can be supplied by solid supplements, such as energy bars.

Rhabdomyolysis—Exertion-related muscle damage causes fatigue, muscle aches, and leads to myoglobin (which looks like blood) in urine. To minimize the risk:

• Increase training intensity gradually to give muscles time to adapt.
  
  
• Maintain a year-round activity/fitness program.
  
  
• Avoid exercise when the temperature and humidity are high unless you have trained for those conditions.
  
  
• Limit exercise during times of illness.
  
  
• Consult your physician if you have predisposing factors (if you take statin drugs or have sickle-cell trait, some viral infections, or are susceptible to hyperthermia).

If rhabdomyolysis is suspected, emergency medical personnel can begin saline infusion and prepare to transport the victim. Blood work (creatine kinase, potassium) will verify the diagnosis (Physician and Sportsmedicine, April 2004).