Water Distribution in Human Body

In human adults, total body water accounts for about 70 percent of the lean body mass. Variations observed are mainly due to age sex, body composition and differences in fat contents. In obese males, water constitutes a lower percentage of body weight (45-60 percent) than in lean individual (55-70 percent). Adult lean females have a low-water content (45-60 percent) and the value in infants can be in the range 65-75 percent. A loss of 10 percent of water in the body is serious, a loss of 20 percent is fatal.

In an adult male of 70 kg body weight, 70 percent of water i.e., 30 liters, is found in intercellular fluids. Of this, about 4 liters are found in bones which do not readily participate in fluid exchange. Nearly, 30 percent of water, about 12 liters, is found in extracellular fluid, three liters of plasma, 8.5 liters of interstitial fluid and one liter of trans-cellular fluid come under extracellular fluid. Trans-cellular fluids are formed by the ‘transport’ or ‘secretory activity’ of cells, e.g., fluids secreted from salivary gland, pancreas etc. Aqueous humour and cerebrospinal fluid are also trans-cellular fluids.

The extracellular fluid contains large quantities of sodium but only small quantities of potassium. Intracellular fluid contains more potassium than sodium. The extracellular fluid contains large quantities of chloride but the concentrations of phosphates and protein in the intracellular fluid are considerably greater than in the extracellular fluid.

Guidelines for Proper Hydration

  • Weigh before and after exercise especially during hot weather.
  • For each pound of body weight lost during exercise, drink 2 cups of fluid.
  • Do not restrict fluids before or during an event.
  • Drink at least 225-450 ml (1-2 cups) of fluid 2 h before practice or competition.
  • Drink at least 110-225 ml of fluid immediately before exercise
  • Drink at least 110-225 ml of fluid every 15-20 min during training and competition
  • Drink at least 225-450 ml of fluid after exercise
  • Drink at least 225 ml of fluid with each meal.
  • Drink at least 225 ml of fluid between meals
  • The replacement drink should contain 80-120 mg sodium per 8 hr
  • The replacement drink should contain 6-8 percent carbohydrate either as glucose polymers or fructose.
  • The drink should be cool.

Reference: Exercise Physiology, Fitness, and Sports Nutrition

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