What occurs when the body loses too much fluid during physical activity?

Dehydration occurs when the body loses more fluid than it takes in. This condition can result from illness; a hot,dry climate; prolonged exposure to sun or high temperatures; not d

What occurs when the body loses too much fluid during physical activity?

Dehydration occurs when the body loses more fluid than it takes in. This condition can result from illness; a hot,dry climate; prolonged exposure to sun or high temperatures; not drinking enough water; and overuse of diuretics or other medications that increase urination. Dehydration can upset the delicate fluid-salt balance needed to maintain healthy cells and tissues.

  • Water accounts for about 60% of a man's body weight. It represents about 50% of a woman's weight.
  • Young andmiddle-aged adults who drink when they're thirsty do not generally have to do anything more to maintain theirbody's fluid balance.
  • Children need more water because they expend more energy, but most children who drinkwhen they are thirsty get as much water as their systems require.
  • Age and dehydration: Adults over the age of 60 who drink only when they are thirsty probably get only about 90% of the fluid they need.
  • Dehydration in children usually results from losing large amounts of fluid and not drinking enough water to replacethe loss. This condition generally occurs in children who have stomach flu characterized by vomiting and diarrhoea, or who can not or will not take enough fluids to compensate for excessive losses associated with feverand sweating of acute illness.
  • An infant can become dehydrated only hours after becoming ill. Dehydration is amajor cause of infant illness and death throughout the world.[1]

There are three main types of dehydration: hypotonic (primarily a loss of electrolytes), hypertonic (primarily loss of water), and isotonic (equal loss of water and electrolytes). The most commonly seen in humans is isotonic. [2]

Body water is lost through the skin, lungs, kidneys, and GI tract. The loss of body water without sodium causes dehydration.

  • Water is lost from the skin, lungs, gastrointestinal tract, and kidneys.
  • Dehydration results when water losses from the body exceed water replacement.
  • It may be caused by failure to replace obligate water losses.

There are several forms of dehydration.

  1. Isotonic water loss occurs when water and sodium are lost together. Causes of isotonic water loss are vomiting, diarrhea, sweating, burns, intrinsic kidney disease, hyperglycemia, and hypoaldosteronism.
  2. Hypertonic dehydration occurs when water losses exceed sodium losses. Serum sodium and osmolality will always be elevated in hypertonic dehydration. Excess pure water loss occurs through the skin, lungs, and kidneys. Etiologies are fever, increased respiration, and diabetes insipidus.
  3. Hypotonic dehydration is mostly caused by diuretics, which cause more sodium loss than water loss. Hypotonic dehydration is characterized by low sodium and osmolality.

The source of water loss relates to the etiologies of dehydration:

  • Failure to replace water loss: altered mentation, immobility, impaired thirst mechanism, drug overdose leading to coma
  • Excess water loss from the skin: heat, exercise, burns, severe skin diseases
  • Excess water loss from the kidney: medications such as diuretics, acute and chronic renal disease, post-obstructive diuresis, salt-wasting tubular disease, Addison disease, hypoaldosteronism, hyperglycemia
  • Excess water loss from the GI tract: vomiting, diarrhea, laxatives, gastric suctioning, fistulas
  • Intraabdominal losses: pancreatitis, new ascites, peritonitis
  • Excess insensible loss: sepsis, medications, hyperthyroidism, asthma, chronic obstructive pulmonary disease (COPD), drugs[3]
  • Healthy adults with access to water rarely become dehydrated.
  • Any adult may develop dehydration as a complication of an illness such as hyperglycemia.
  • Data shows that older adults are more likely to develop dehydration. The elderly population is also 20% to 30% more prone to developing dehydration due to immobility, impaired thirst mechanism, diabetes, renal disease, and falls.[4]

Characteristics/Clinical Presentation[edit | edit source]

Increased thirst, dry mouth, light-headedness, fatigue, impaired mental focus, low urine output, dry skin, inability to produce tears, sunken eyes are the signs of dehydration. [5]Mild Dehydration
Moderate Dehydration
Severe Dehydration

  • flushed face
  • thirst
  • dry, warm skin
  • cannot pass urine or reduced amounts, dark, yellow coloring
  • light shade of yellow urine
  • weakness
  • cramping in arms and legs
  • unwell
  • headaches
  • dry mouth/lips, dry tongue; with thick saliva
  • lightheadedness, worse when standing
  • irritable or sleepy
  • crying with no or few tears (mainly in children)
  • low BP (postural hypotension[6])
  • headaches[6]
  • darker shade of yellow urine
  • fainting
  • severe muscle contractions in arms, legs, stomach, and back
  • convulsions
  • bloated stomach
  • heart failure
  • sunken fontanelle (soft spot on infant's head)
  • sunken dry eyes
  • skin loses firmness and looks wrinkled
  • lack of elasticity of skin
  • rapid and deep breathing
  • fast, weak pulse
  • decline consciousness
  • increased heart rate (radial pulse may be undetectable)
  • decreased or low blood pressure
  • effects are more pronounced
  • peripheral cyanosis
  • confusion, lethargy, irritability[6]
  • cold hands and feet[6]
  • unable to urinate[6]
  • hypovolaemic shock
  • effects are more pronounced
  • death may occur, if rehydration is not started quickly

Increased tiredness, headaches, nausea, and paresthesias are experienced at about 5% to 6% water loss. With 10% to 15% fluid loss, may experience symptoms of muscle cramping, dry and wrinkly skin, beginning of delirium, painful and/or decreased urine output, and decline in eyesight.Losses of water greater than 15% are usually fatal[7].

When to seek medical attention[edit | edit source]

  • Constant or increased vomiting for greater than a 24 hour period
  • Diarrhoea greater than two days
  • Fever over 101o degrees
  • Decreased urine production
  • Weakness
  • Confusion[8]

Both physical and mental exams help to diagnose dehydration.

  • A patient presenting symptoms such as disorientation, low blood pressure, rapid heartbeat, fever, lack of sweat, and inelastic skin will usually be considered dehydrated.
  • Blood tests are often employed to test kidney function and to check sodium, potassium, and other electrolyte levels (chemicals that regulate hydration in the body and are crucial for nerve and muscle function). A urine analysis will provide very useful information to help diagnose dehydration. In a dehydrated person, urine will be darker in color and more concentrated.
  • To diagnose dehydration in infants, doctors usually check for a sunken soft spot on the skull. They may also look for a loss of sweat and certain muscle tone characteristics.[2]

If dehydration is not checked, it can lead to serious complications; these can include:

  • The principle differential of dehydration in adults is the loss of body water versus the loss of blood.
  • This is important because blood loss should be replaced with blood, while water loss should be replaced with fluid.
  • The next point to consider is the differential diagnosis of the cause of dehydration (see Etiology above)[3]

Dehydration must be treated by replenishing the fluid level in the body. This can be done by consuming clear fluids such as water, clear broths, frozen water or ice pops, or sports drinks (such as Gatorade). Some dehydration patients, however, will require intravenous fluids in order to rehydrate. People who are dehydrated should avoid drinks containing caffeine such as coffee, tea, and sodas.

Underlying conditions that are causing dehydration should also be treated with the appropriate medication. This may include medication available to purchase over-the-counter or online, such as anti-diarrhea medicines, anti-emetics, and anti-fever medicines.[2]

Physical Therapy Management & Prevention[edit | edit source]

There is no direct physical therapy intervention for dehydration in the severe category; however, prevention and fluid replacement orally is something physical therapists can influence through patient education.

Patients should be educated about the signs and symptoms of dehydration in order to know when they may need to seek help. This is done by proper knowledge of hydration[10].

Environmental Factors[10][edit | edit source]


  • Being outside on a hot or humid day can cause your body to need more fluids
  • It is recommended by the American Heart Association to drink water before being outdoors in the heat. This way you do not have to play catch up with Hydration when strain has already been placed on the heart.


  • Fluid intake also needs to be increased in cooler environments.
  • Cool temperatures may blunt thirst
  • Inhalation of cold, dry air increases warmth and moisture in the lungs which causes water vapor to be exhaled
  • Physical Activity in the cold can increase respiratory water losses by 15-45 mL per hour
  • Insulated clothing can also increase perspiration, increasing water loss

Hydration and Exercise

Before exercise: Drink 12-20oz of fluid 2 hours leading up to exercise

During Exercise:

  • <1-hour drink 16-30 oz of water
  • 1-3 hours drink 16-30 oz 6-8% CHO, sodium drink per hour of exercise
  • >3 hours similar to guidelines for 1-3 hours but increase sodium intake

Avoid caffeine or alcohol in beverages due to their diuretic effects

Avoid hyponatremia which can occur by drinking too much fluid. therefore, diluting sodium

Monitor dehydration with changes in body weight and urine color. Each pound lost during exercise, drink 15-16oz of fluid[13]

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