Febbraio, unpublished observations). It is also
recommended that the carbohydrate beverage
be ingested into recovery to replenish intramus-
cular glycogen stores and promote rehydration,
especially important for those individuals
repeatedly exercising in a hot environment.
As previously discussed, there is some evi-
dence to suggest that protein catabolism is
increased during exercise in the heat. One may be
tempted to recommend that protein intake be
increased prior to and during such exercise.
However, it must be noted that there is a relative
paucity of research examining protein require-
ments during exercise in the heat and more is
required before definitive recommendations
can be made. Likewise, there is some evidence
to suggest that oxyradical generation may be
increased via the combination of exercise and
heat stress and it may be of some benefit to sup-
plement those undertaking repeated exercise
in a hot environment with antioxidants such
asa-tocopherol (vitamin E) and ascorbic acid
(vitamin C). This recommendation is specula-
tive, however, since the hypothesis that such
supplementation is advantageous during
exercise in the heat is yet to be experimentally
investigated.
The deleterious effects of dehydration during
exercise, especially that which is conducted in a
hot environment, have been well documented.It would be desirable to hyperhydrate before
exercise and, as has been demonstrated, glycerol
ingestion may provide some benefit in achieving
hyperhydration by attenuating urine output. It
appears that a regime consisting of 1 g glycerol ·
kg–1body weight in approximately 2 l of fluid
ingested in the 120 min prior to exercise provides
some benefit during subsequent exercise (Lyons
et al. 1990). Competitive athletes should, how-
ever, experiment with this regime during train-
ing, since not all individuals may respond
favourably to glycerol hyperhydration.
In summary, during exercise in the heat, a
balance between preventing hyperthermia and
maintaining adequate fuel supply to fuel muscle
contraction must be maintained. In order to
achieve this, athletes need to closely moni-
tor hydration levels and carbohydrate intake
leading up to exercise. Daily monitoring of body
weight and ensuring that urine is pallid will
provide a guide to hydration status. During com-
petition, a 4–8% carbohydrate/fluid/electrolyte
solution should be ingested at approximately
400 ml every 15 min and such ingestion should be
maintained during recovery to ensure fluid and
energy replacement. Other dietary modifications
such as increased protein intake, antioxidant
supplementation and glycerol hyperhydration
may provide some benefit but further research
in these areas is required before definitiveexercise at climatic extremes 505
50–5–10–15–2039.5
39
38.5
38
37.5
37
36.5120
100
80
60
40
20
0
0 20 40 60 80 100 120 0 20 40 60 80 100 120
Time (min) Time (min)Change in PV (%)
Rectal temperature ( C)Exercise time (min)CON 4.2%
CHO7%
CHO14%
(a) (b) (c) CHO
*Fig. 38.4The change in (a) plasma volume (PV), (b) rectal temperature, and (c) time to exhaustion, while
consuming a placebo (CON, ) or carbohydrate (CHO) beverage of differing concentrations: 4.2% CHO (), 7%
CHO () or 14% CHO () during fatiguing exercise at 70% V
.
o2max.in 33°C conditions. *, difference (P<0.05) from
other trials. Data expressed as mean ±SE. Data from Febbraio et al. (1996a).