Authors : Dabre P. C. and Pingle P. V.
Page Nos : 213-215
Description :
Prolonged exercise leads to progressive water and electrolyte loss from the body as sweat is
secreted to promote heat loss. The rate of sweating depends on many factors and is increased in
proportion to the work rate and the environmental temperature and h
umidity. Sweat rate is highly
variable between individuals, and can exceed 21 h
-
1 for prolonged periods. Since it is established that
dehydration will impair exercise capacity and can pose a risk to health, the intake of fluid during exercise
to offset swe
at loss is important. Fluid intake is also aimed at providing a source of substrate, usually in
the form of carbohydrate. The availability of ingested fluids may be limited by gastric emptying or by
intestinal absorption. Gastric emptying of liquids is slo
wed by the addition of carbohydrate in proportion
to the carbohydrate concentration and osmolality of the solution. With increasing glucose concentration,
the rate of fluid delivery to the small intestine is decreased, but the rate of glucose delivery is i
ncreased.
Water absorption in the small intestine is a passive process and is stimulated by the active absorption of
glucose and sodium. The optimum fluid for rehydration during exercise depends on many factors,
particularly the intensity and duration of t
he exercise, the environmental conditions, and the individual
physiology of the athlete. There is no advantage to fluid intake during exercise of less than 30 min
duration. The composition of fluids to be used will depend on the relative needs to replace w
ater and to
provide substrate. Where rehydration is a priority the solution should contain some glucose and sodium
and should not exceed isotonicity: this will require the glucose concentration to be low (20
-
309 g l
-
1) or
the substitution of glucose polyme
rs, and the sodium content to be high (perhaps as much as 60 mmol l
-
1). Where substrate provision is more important, a more concentrated solution, incorporating large
amounts of glucose polymers in concentrations of 150
-
200 g l
-
1, is to be preferred. To mi
nimize the
limitation imposed by the rate of gastric emptying, the volume of fluid in the stomach should be kept as
high as is comfortable by frequent ingestion of small amounts of fluid. Addition of sodium, and perhaps
also of potassium, may be important
for rehydration after exercise
