NUTRITION IN SPORT

hypohydration reduces maximal aerobic power
in temperate climates. In hot climates, Craig
and Cummings (1966) demonstrated that small
(2% BWL) to moderate (4% BWL) water deficits
resulted in a large reduction of maximal
aerobic power. Likewise, their data indicate a
disproportionately larger decrease in maximal
aerobic power with an increased magnitude of
body water deficit. It seems environmental
heat stress has a potentiating effect on the reduc-
tion of maximal aerobic power elicited by
hypohydration.
The physical exercise capacity (exercise to
fatigue) for progressive intensity exercise is
decreased when hypohydrated. Physical exer-
cise capacity is decreased by marginal (1–2%
BWL) water deficits that do not alter V

.
o2max.
(Caldwellet al. 1984; Armstrong et al. 1985a), and
the decreases are larger with increasing water
deficits. Clearly, hypohydration results in larger
decrements of physical exercise capacity in hot
than in temperate climates (Armstrong et al.
1985a). It appears that the thermoregulatory
system, perhaps via increased body tempera-
tures, has an important role in the reduced exer-
cise performance mediated by a body water
deficit. Figure 16.2 presents the relationship
between hypohydration level and V

.
o2max.decre-
ment or physical exercise capacity decrement
during heat exposure (Craig & Cummings 1966;
Pinchanet al. 1988). Note that for a given hypo-
hydration level, greater decrements are observed
for physical exercise capacity than V

.
o2max..
Studies have demonstrated that hypohydra-
tion can impair athletic endurance exercise

performance. Armstrong and colleagues (1985a)

studied the effects of a body water deficit on

competitive distance running performance. They

had athletes compete in 1500-, 5000- and 10 000-

m races when euhydrated and when hypohy-

effects of dehydration and rehydration 219

50

40

30

20

10

0

50

40

30

20

10

0

01234 1 2 3 4

(a) Body water loss (%) (b) Body water loss (%)

VO

2 max

decrease (%)

. Exercise capacity (%)

Fig. 16.2Relationship between
hypohydration level and (a)
V
.
o2max.decrement, and (b)
physical exercise capacity
decrement during heat exposure.
, from Craig and Cummings
(1966);, from Pinchan et al.
(1988).

Fig. 16.3With many major competitions held in hot

environments, the outcome of races may depend

on maintaining hydration status. Photo ©

Allsport / Martin.