exercise have shown mixed results (Miller et al.
1983; Latzka et al. 1996). There have been some
suggestions of improved performance after
administration of glycerol and water prior to
prolonged exercise (Montner et al. 1996) but some
earlier work clearly indicated that it did not
improve the capacity to perform prolonged exer-
cise (Burge et al. 1993).
Postexercise rehydration
Rehydration and restoration of sweat electrolyte
losses are both crucial parts of the recovery
process after exercise where significant sweat
losses have occurred, and these issues are
covered in detail in Chapter 19. In most sports,
there is a need to recover as quickly and as com-
pletely as possibly after training or competition
to begin preparation for the next event or train-
ing session. The need for replacement will obvi-
ously depend on the volume of sweat lost and on
its electrolyte content, but will also be influenced
by the amount of time available before the next
exercise bout. Rapid rehydration may also be
important in events where competition is by
weight category, including weightlifting and the
combat sports. It is common for competitors in
these events to undergo acute thermal and exer-
cise-induced dehydration to make weight, with
weight losses of 10% of body mass sometimes
being achieved within a few days: the time inter-
val between the weigh-in and competition is nor-
mally about 3 h, although it may be longer, and is
not sufficient for full recovery when significant
amounts of weight have been lost, but some
recovery is possible. The practice of acute dehy-
dration to make weight has led to a number of
fatalities in recent years, usually where exercise
has been performed in a hot environment while
wearing waterproof clothing to prevent the
evaporation of sweat, and should be strongly
discouraged, but it will persist and there is a need
to maximize rehydration in the time available.
An awareness of the extent of volume and
electrolyte loss during exercise will help plan the
recovery strategy. Where speed of recovery is
essential, a dilute glucose solution with added
sodium chloride is likely to be most effective in
promoting rapid recovery by maintaining a high
rate of gastric emptying and promoting intestinal
water absorption: a hypotonic solution is likely
to be most effective (Maughan 1994). Complete
restoration of volume losses requires that the
total amount of fluid ingested in the recovery
period exceeds the total sweat loss: the recom-
mendation often made that 1 litre of fluid should
be ingested for each kilogram of weight lost
neglects to take account of the ongoing loss of
water in urine, and it is recommended that the
volume of fluid ingested should be at least 50%
more than the volume of sweat loss (Maughan &
Shirreffs 1997).
It is more difficult, because of the wide
interindividual variability in the composition of
sweat, to make clear recommendations about
electrolyte replacement. It is clear, however, that
failure to replace the electrolytes lost (principally
sodium, but to some extent also potassium) will
result in a fall in the circulating sodium concen-
tration and a fall in plasma osmolality, leading to
a marked diuresis. The diuretic effect is observed
even when the individual may still be in negative
fluid balance. If sufficient salt is ingested
together with an adequate volume of water, fluid
balance will be restored, and any excess solute
will be excreted by the kidneys (Maughan &
Leiper 1995). A relatively high sodium content in
drinks will also be effective in retaining a large
proportion of the ingested fluid in the extracellu-
lar space, and maintenance of a high plasma
volume is important for maintenance of cardio-
vascular function (Rowell 1986).Conclusion
Water and electrolyte losses in sweat will result
in volume depletion and disturbances of elec-
trolyte (especially sodium) balance. Sweat loss
depends on many factors, including especially
environmental conditions, exercise intensity and
duration, and the individual characteristics of
the athlete. Replacement of losses will help main-
tain exercise capacity and reduce the risk of heat
illness. Replacement may be limited by the rates