ingestion during exercise (Costill & Hargreaves
1992), since this would provide necessary
glucose while allowing for optimal gastric emp-
tying and intestinal absorption (Mitchell et al.
1989; Rehrer et al. 1989; Gisolfiet al. 1991). It has
been suggested, however, that increasing the
carbohydrate content of a fluid beverage may be
beneficial during exercise in cooler conditions
since the requirement for optimal fluid delivery
may be less important, due to the reduction in
thermoregulatory stress, while the necessity for
sufficient circulating glucose levels is main-
tained. We have recently tested this hypothesis
and found that increasing the carbohydrate
content of a fluid beverage which is ingested
during exercise in a cool environment is not
advantageous (Fig. 38.1). While such a practice
does elevate blood glucose levels, it results in
increased gastrointestinal discomfort, a less than
efficient maintenance of plasma volume and a
reduction in exercise performance relative to the
ingestion of a 7% carbohydrate beverage (Feb-
braioet al. 1996a). Therefore, when the endogen-
ous heat produced by exercise in cool ambient
conditions is sufficient to offset body heat loss,
feeding strategies recommended during exercise
in comfortable ambient temperatures should be
adhered to.During exercise in extremely cold environ-
ments which results in a fall in body core temper-
ature, any dietary modification which results in
an increase in whole-body metabolic rate, which
would generate warmer body temperatures and
improve cold tolerance, would be most benefi-
cial. As a result, recent research has focused on
administration of many ergogenic aids designed
to increase thermotolerance during cold stress.
These ergogenic aids include hormones, phar-
macological agents and nutrients. Administra-
tion of the pharmacological agent dinitrophenol
(Hallet al. 1948) and hormones such as thyroxin,
catecholamines, cortisol and growth hormone
(Sellers 1972; Le Blanc 1975) in cold exposed
animals results in a delay in the onset of
hypothermia. However, while these studies
provide useful information regarding the mecha-
nisms for the induction of thermogenesis, it is
impractical to suggest that they be taken by
humans as ergogenic aids during exercise and
cold stress because of the obvious health risks.
It is possible, that ingestion of b-adrenergic
agonists such as caffeine, ephedrine or theo-
phylline may improve cold tolerance, although
the literature which has examined such a phe-
nomenon has produced conflicting results.
Ingesting the combination of ephedrine and caf-exercise at climatic extremes 499
1086421050–5–10–15250200150100500Glucose (mmol–1.l
)Change in PV (%)Time (min)0 50 100 150 200 250
Time (min) Time (min)0 50 100 150 200 250 CON LCHO HCHO
Trial**†**†
*†**†*†††††(a) (b) (c)
Fig. 38.1(a) Plasma glucose, (b) change in plasma volume (PV), and (c) time to exhaustion while consuming a
placebo (CON, ), 7% carbohydrate (LCHO, ) or 14% carbohydrate (HCHO, ), beverage during fatiguing
exercise at 70% V
.
o2max.in 5°C conditions. *, difference (P<0.05) compared with CON; †, difference (P<0.05)
compared with HCHO. Data expressed as means ±SE (n=6). From Febbraio et al. (1996a).