Chapter 5: Physiology and Fitness




I. Resources

PowerPoint slides, Chapter 5

Selected Nutrition References

Liters-to-gallons conversion chart

Fitness worksheets


II. Teaching Points


A. Food and nutrition (p. 44)

  1. It takes several hours for most foods to become available to the body as energy:  “What you eat today is what you run on tomorrow.” 
  2. Moral of the story: Eat well today in case you are called out tomorrow.
  3. Humans in arctic or cold environments consume (burn) more calories than those in warm climates¾perhaps as much as 2,000 extra calories per day. 
    1. This makes long-lasting, high-energy foods a more critical factor in cold weather than other climates.
  4. Food should be eaten only when there is enough water to drink.  Do not eat if water is scarce.


B. Water and hydration (p. 45)

  1. The human body may be able to survive for as long as a month without food but only for a matter of days without water.
  2. Two thirds of one’s body weight is water. 
    1. Two thirds of this water is inside body cells and the other one third is in the veins, body cavities, and other spaces.
  3. No other nutrient affects athletic or work performance more than water.
  4. Decreases in normal levels:
    1. 1% decrease in normal levels triggers thirst. 
    2. 10% drop impairs thinking and judgment. 
    3. 20% loss is usually fatal.
  5. Water requirements:
    1. An inactive person requires a minimum of 1.2 liters of water a day to keep all body systems functioning properly. 
    2. Small levels of activity (walking, normal daily actions) can easily double this requirement (2.4 liters). 
    3. High humidity can again double the requirement (4.8 liters), as can physical exertion. 
    4. It is not unusual to require 8 to 10 liters of water per day under extreme conditions. Physical exertion under hot desert conditions can cause the loss of 2 to 3 liters of water per hour to sweat.


  1. To re-hydrate properly, drink water slowly until the urine is a pale yellow color.  (Deep amber urine signifies dehydration whereas pale yellow signifies adequate hydration).


  1. Sports drinks such as Gatorade® or an equivalent can be used for re-hydration as well and will also help replace electrolytes lost through sweating.


C. The heat balance equation (p. 46)

  1. To maintain a normal body temperature one must:
    1. Control heat production¾proper health and nutrition
    2. Control heat loss¾proper clothing system
  2. The body’s primary method of regulating temperature involves adjusting the flow of heated blood between its core and periphery.
  3. Generally blood is pushed to the skin and extremities for cooling and shunted to the core (brain, heart, lungs) to preserve heat.
  4. The body produces heat:
    1. Through metabolism; and
    2. Through muscle movement; and
    3. May absorb heat from its environment
  5. To increase body temperature, isometric exercises and the act of shivering are preferred over strenuous muscular activity because they produce less perspiration.


D. Methods of heat transfer¾Loss of heat to the environment. (p. 47)

  1. Radiation
    1. When heat escapes from bare skin or reaches the outer layer of clothing
    2. The higher the temperature of the radiating surface, the faster heat will be lost through this method.


  1. Conduction
    1. When heat is transferred from hot objects to cold objects
    2. The greater the temperature difference between the two objects, the faster heat is conducted.


  1. Convection
    1. As free moving air next to the body absorbs heat, it expands and rises.  Immediately, new cooler air moves in and replaces this moving war air.  This is natural convection. 
    2. To prevent convective heat loss, get out of the wind.


  1. Evaporation
    1. The majority of evaporative heat loss occurs through sweating.
    2. Even without sweating, it is estimated that one and one half (1½)pints of a person’s daily water loss is due to “insensible perspiration” or the continuous, imperceptible drying out of the skin. 


  1. Respiration
    1. Respiratory heat loss is actually a form of evaporation. 
    2. In most cold circumstances, this manner of heat loss is considered insignificant. 
    3. In an extremely cold environment where any calorie loss is important, the addition of a re-breather (scarf or improvised thickness of material) that will preheat the inhaled air can significantly reduce respiratory heat loss.


E. Admitting limitations (p. 55)

  1. You must make a realistic assessment of your physical abilities without being nostalgic and recalling earlier athletic achievements. 
  2. Knowing when to stay out of the field is a prime example of when your brain becomes your primary survival tool.  
  3. Admitting your physical limitations is preferred to finding out about your lack of conditioning after a futile and dangerous attempt at working in the field. 
  4. Remember:
    1. When search and rescue personnel become disabled, injured, or ill, focus is drawn away from the victim. 
    2. It can also endanger fellow crew members.