addition to, an increased CHO availability to the
contracting muscles.
Medium-chain triacylglycerol ingestion
during exercise
Recently it has been suggested that medium-
chain triacylglycerol (MCT) ingestion during
cycling exercise may provide an additional fuel,
thereby possibly sparing endogenous CHO
stores and improving exercise capacity. MCT is
derived from coconut oil and contains medium-
chain fatty acids which are rapidly absorbed and
oxidized (Massicotteet al.1992; Jeukendrupet al.
1995, 1996a). However, despite its rapid metabo-
lism, several studies show that ingestion of small
amounts of MCT (25–45 g of MCT over the course
of 1–3 h) may not be sufficient to alter fat oxida-
tion, glycogen breakdown or cycling perfor-
mance (Ivyet al.1980; Jeukendrupet al.1995,
1996a, 1996b, 1998). Larger amounts generally
cause gastrointestinal problems and can there-
fore not be recommended.
Fluid intake during exercise
Besides CHO, cyclists need to maintain their
water balance. Exercise-induced dehydration
may augment hyperthermia and multiple
studies show that prevention of dehydration by
fluid ingestion improves performance (see
Chapter 16). Dependent on the weather condi-
tions, fluid losses may vary from 0.5 to up to
almost 3 l · h–1. Individual fluid loss can be esti-
mated from weight loss although this also
includes a small amount of weight loss due to
glycogen and fat oxidation. During 90 min of
exercise, 100–300 g of glycogen and fat may be
oxidized. By regularly monitoring body weight
before and after training sessions and competi-
tions, it is possible to predict the fluid loss in a
certain race. However, since the main limitation
seems to be the amount of beverage that can be
tolerated in the gastrointestinal tract, in most
conditions it is advisable to drink as much as pos-
sible. Completely compensating for sweat loss
by fluid consumption may not always be pos-
568 sport-specific nutrition
sible because sweat losses may exceed 2 l · h–1and
ingestion of such amounts cannot be tolerated by
the gastrointestinal tract. Observations in profes-
sional cyclists during the Mediterranean Tour in
France and the Ruta del Sol in Spain show that
riders lose about 2.1–4.5 kg during a 4–5-h stage,
indicating that even cyclists who are well aware
of the importance of drinking cannot drink suf-
ficiently during a race (G. Leinders & A.E.
Jeukendrup, unpublished findings). Therefore,
fluid and CHO consumption is usually limited
by the practical situation and by the amount of
drink that can be tolerated after ingestion. This
highlights the importance of making ‘drinking
during exercise’ a part of the regular training
programme.
Also during high-intensity exercise of about
1 h duration, water seems to be beneficial to per-
formance. Belowet al.(1995) showed that water
ingestion, independently of CHO, improved
time-trial performance (time trial of about 10 min
duration after 50 min at 80% V.
o2max.), while
the CHO and water had an additive effect on
performance.
Palatability of drinks and food is a very impor-
tant aspect because it will stimulate consumption
and with it increase the intake of fluid and CHO.
In addition, taste and flavour perception may
also influence the rate of gastric emptying.
Disliked flavour or aroma may slow gastric
emptying and may even cause nausea.Nutrition during exercise: some observations
in professional cyclists
In general, professional cyclists tend to eat solid
food during the first hours of their stages, usually
consisting of chunks of banana, apple, white
bread with jamor rice cakes. The pace during the
first hours is usually slow and there is plenty of
time to digest the solid food. As soon as the speed
increases, the cyclists switch to fluid ingestion
and solid food will only be eaten when the speed
drastically drops or their stomachs feel empty.
Since they have only two bottles on their bike,
usually containing 0.5 l each, they have to get
new bottles regularly during the race. Profes-