suggests that sodium in fluid replacement beverages is important for maintaining the osmotic drive for drinking during recovery from prolonged exertion (Nose et al., 1988).

Summary of Effects of Water and Saline Replacement on Homeostasis During Prolonged Exertion

Fluid replacement during strenuous prolonged exertion is unquestionably beneficial in minimizing the adverse effects of dehydration on cardiovascular function and temperature regulation. Although not all studies have demonstrated significant improvements in all markers of cardiovascular function and temperature regulation, there is overwhelming cumulative evidence that fluid replacement lowers cardiovascular strain and improves thermoregulation when compared with cardiovascular strain and thermoregulation under conditions in which fluid is withheld during prolonged exertion.

The value of electrolytes added to fluids consumed during prolonged exertion has yet to be conclusively demonstrated, but individuals susceptible to hyponatremia with water feedings alone may profit from electrolyte supplements. Also, sodium may be important for optimal rehydration following prolonged exertion. Furthermore, the low concentrations of electrolytes found in most fluid replacement beverages (Table 3-2) are apparently benign and may encourage fluid consumption by enhancing beverage palatability.

Table 3-2 Approximate Composition of Beverages That May Be Consumed During Prolonged Exercise

Beverage Type

Sodium (mM)

Potassium (mM)

Sucrose (%)

Glucose (%)

Polymers (%)

Fructose (%)

Apple juice

2

31.0

2.9

9.0a

-

-

Body fuel 450

16

2.0

-

-

4.5

-

Cola drinks

4

0.1

3.7

6.8a

-

-

Exceed

10

5.0

-

-

5.0

2.0

Gatorade

20

3.0

4.0

2.0

-

-

Gookinaid ERG

16

10.0

-

5.0

-

-

Isostar

23

5.0

6.8

0.1

0.1

-

Lemonade

1

5.0

2.6

7.0a

-

-

Orange juice

1

52.0

7.0

5.0a

-

-

a variable mixture of glucose and fructose



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