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After studying this chapter, the reader should be able to:

  • 8.1 Describe how gender, age, diet, and environment affect hydration status.

  • 8.2 Define euhydration, hyponatremia, and dehydration.

  • 8.3 Identify populations at greatest risk for hyponatremia and dehydration.

  • 8.4 Identify ways to recognize and treat hyponatremia and dehydration.

  • 8.5 List ways that hydration status affects athletic performance.

  • 8.6 Apply the most up-to-date and scientifically sound hydration recommendations before, during, and after exercise.

  • 8.7 Calculate sweat rate using the protocol provided by USA Track and Field.



  • acclimatization Physiological changes that occur in response to repeated exposure to an environmental condition such as heat or high altitude.

  • aldosterone A hormone released by the adrenal gland that helps to maintain normal blood sodium levels by increasing the kidney's reabsorption of sodium and decreasing the amount of sodium lost in sweat.

  • antidiuretic hormone A hormone released by the anterior pituitary that helps to maintain blood volume in the face of dehydration by increasing water reabsorption in the kidneys and decreasing the amount of urine produced.

  • cold diuresis Increased urine production and excretion that occurs in extreme cold as a result of peripheral vasoconstriction, high blood sugar, and decreased renal reabsorption of water.

  • diuresis Increased urine production and excretion.

  • encephalopathy Loss of normal function of brain tissue, which may result from a wide variety of conditions including hyponatremia.

  • euhydration A state of "normal" body water content; the perfect balance between "too much" and "not enough" fluid intake.

  • exertional hyponatremia Abnormally low blood sodium level that results from excessive intake of low-sodium fluids during prolonged endurance activities.

  • heat cramps (exercise-associated muscle cramps) Muscle spasms resulting from loss of large amounts of water and electrolytes during physical exertion; typically affect the abdomen, arms, and calves.

  • heat exhaustion A heat-related illness that occurs after prolonged exposure to heat without adequate replacement of fluids and electrolytes; symptoms include heavy sweating, fatigue, and vomiting. Heat exhaustion is less serious than heat stroke.

  • heat stroke A severe heat-related illness with extreme overheating resulting from prolonged exposure to heat without adequate replacement of fluids and electrolytes; symptoms include lack of sweating, strong and rapid pulse, disorientation, and loss of consciousness. Often fatal without rapid treatment.

  • hypothalamus A portion of the brain responsible for regulating body temperature, among many other functions.

  • hypothermia Condition in which the core body temperature falls below 35°C (95°F), the minimal temperature necessary for normal metabolism and body function.

  • postural hypotension The pooling of blood in the legs and inadequate blood supply to the upper body that causes dizziness, weakness, and collapse; often occurs with dehydration and heat stress and may be confused with heat stroke.

  • rhabdomyolysis Breakdown of skeletal muscle tissue and release of contents into the bloodstream that sometimes leads to kidney failure; caused by dehydration and heat stress.


Milliliters to ounces: 240 ml = 8 oz = 1 cup ...

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