Introduction
The relationship between nutrition and exercise
has been a major scientific interest area for over
150 years. With the popularization of the muscle
biopsy technique, arteriovenous (a-v) balance
measurements and, more recently, the use of
isotope tracers as metabolic probes during exer-
cise, it has become possible to clearly investigate
the role of nutrition in exercise physiology and
biochemistry. Accordingly, growth in this area
has increased exponentially. Much of the
research which has examined the interaction
between nutrition and exercise has been con-
ducted in comfortable ambient conditions. It is
clear, however, that environmental temperature
is a major practical issue one must consider when
examining nutrition and sport. In extremely
low ambient temperatures, when the gradient
between the skin and surrounding environment
is high, the rate of endogenous heat production,
even during exercise, may be insufficient to offset
body heat loss. In these circumstances, responses
are invoked to reduce heat loss and increase heat
production. In contrast, when exercise is con-
ducted in very high ambient temperatures, the
gradient for heat dissipation is significantly
reduced, which results in changes to thermoreg-
ulatory mechanisms designed to promote body
heat loss. In both climatic extremes, these physio-
logical adaptations ultimately impact upon hor-
monal and metabolic responses to exercise which
act to alter substrate utilization. Hence, environ-
mental temperature is an important factor to
consider when determining optimal nutritional
strategies for exercise performance.Exercise in a cold environment
Cold stress or attenuated
exercise-induced hyperthermia?
Unlike heat, which can only serve to augment the
exercise-induced increase in body temperature, a
cold environment may invoke varied physiologi-
cal responses during exercise. These responses
depend on whether the interaction between the
environment and the exercising organism pro-
motes excessive heat loss or attenuates the
normal rise in body core temperature associated
with exercise. Most studies which have observed
relative hypothermia during exercise have done
so using swimming as the mode of exercise
(Holmer & Bergh 1974; Galbo et al. 1979; Doubt
& Hsieh 1991), since water is a much greater
thermal conductant than air. In contrast, when
exercise has been conducted in cold air environ-
ments ranging from 3 to 9°C, an attenuated rise,
rather than a fall in body core temperature, has
been observed (Jacobs et al. 1985; Febbraio et al.
1996a, 1996b). The severity of the ‘cold stress’ is
an important consideration when examining
nutritional requirements since a fall in body tem-
perature will result in shivering thermogenesis
(Webb 1992) and an enhanced sympathoadrenal
response (Galbo et al. 1979), while an attenuated
rise in body temperature blunts the exercise-
induced increase in adrenaline secretion