activities apart from training, and of the presence
or absence of air conditioning in living and sleep-
ing accommodation. The training status of the
individual will influence the amount of work
that is performed, and thus the total heat load,
but also influences the sweating response to a
standardized heat stress. It is often reported that
the sweating response is enhanced by training,
but Piwonka et al. (1965) showed that trained
runners sweated less than untrained men when
they walked at the same speed on a treadmill
in the heat (40°C), but that they increased their
sweating rate more in response to a rise in core
temperature. The usual response to a period of
acclimatization to heat is an enhanced sweating
response, resulting in an increase, rather than a
decrease, in fluid requirements as an individual
becomes adapted to living and training in the
heat (Sawka 1988).
The daily water requirement of athletes living
and training in the heat will be determined pri-
marily by the sweat losses during training, but
there may also be substantial losses during the
remainder of the day if this is spent outdoors
or if air conditioning is not available. Water
requirements for sedentary individuals, and this
generally includes coaches, doctors, administra-
tors and other team support staff, may be two- or
threefold higher than the requirement when
living in a temperate climate (Adolph &
Associates 1947). Respiratory water losses, while
relatively small at sea level (amounting to about
200 ml · day–1) will be increased approximately
twofold in regions of low humidity, but may be
as high as 1500 ml · day–1during periods of hard
work in the cold dry air at altitude (Ladell 1965).
To these losses must be added insensible loss
through the skin (about 600 ml · day–1) and urine
loss, which will not usually be less than about
800 ml · day–1.
Chapter 15 discusses the sex and age differ-
ences found in sweating rates and patterns.
The extent of sweat loss during training or
competition is easily determined from changes in
body mass adjusted for food or fluid intake and
for urinary or faecal loss. The relatively small
changes in body mass resulting from respiratory
water loss and substrate oxidation are usually
neglected in the field situation: respiratory water
losses will, in any case, represent a water deficit
that should be replaced. There is a large amount
of information in the published literature on
sweat losses in different sports, and much of that
information has recently been collated (Rehrer &
Burke 1996). The relationship between exercise
intensity and sweat loss is seen most clearly in
the simple locomotor sports such as running or
cycling. Figure 17.1 shows that, when exercise is
carried out in the laboratory under standardized
conditions of environment, clothing and exercise
intensity, the sweating rate is closely related to
ambient temperature, with relatively little
variation between individuals. It is clear from
Fig. 17.2, however, which shows sweating rate in
a heterogeneous group of marathon runners, that
the variation between individuals is large,
even at the same running speed (Maughan 1985):
the total sweat loss for these runners, however,
was unrelated to the finishing time.water and electrolyte loss and replacement 227
00.5Temperature (ºC)Sweat rate (l.h
–1
)21 311.01.54 110.650.781.150.55Fig. 17.1Mean sweat rate for eight male subjects
exercising to the point of exhaustion on a cycle
ergometer at an exercise intensity corresponding to
about 70% of V
.
o2max.at different ambient
temperatures. Values are mean±SEM. Adapted from
Galloway and Maughan (1997).