Introduction
Muscle glycogen depletion and/or hypogly-
caemia are associated with fatigue during pro-
longed strenuous exercise (Hermansen et al.
1967; Coyle et al.1986), highlighting the critical
importance of carbohydrate (CHO) availabil-
ity for intramuscular adenosine triphosphate
supply (Norman et al.1987; Sahlin et al.1990;
Spenceret al.1991). In the early part of this
century, the benefit of CHO ingestion during pro-
longed exercise was recognized in a classic field
study (Gordon et al.1925). Over the years since,
numerous controlled, laboratory studies have
demonstrated that ingestion of CHO during pro-
longed, strenuous exercise results in enhanced
exercise performance. Many studies have used
exercise time to fatigue as their measure of
endurance capacity and this is increased by CHO
ingestion (Coyle et al.1983, 1986; Björkman et al.
1984; Coggan & Coyle 1987, 1989; Sasaki et al.
1987; Spencer et al.1991; Davis et al.1992; Wilber
& Moffatt 1992; Tsintzas et al.1996a, 1996b).
Recently it has been argued that time to fatigue
is not a reliable test of endurance performance
(Jeukendrup et al. 1996); however, in well-
motivated subjects, who have been familiarized
with the testing procedures, it remains a useful
laboratory test for elucidating mechanisms of
fatigue. Nevertheless, there are no Olympic
events in ‘exercise time to fatigue’, and it is
perhaps more appropriate to assess endurance
performance by tests that measure the time taken
to complete a standard task or the work output in
a certain amount of time. Using such tests, CHO
ingestion has been shown to improve perfor-
mance as measured by enhanced work output or
reduced exercise time (Neufer et al.1987; Coggan
& Coyle 1988; Mitchell et al.1989; Williams et
al.1990; Murray et al.1991; Tsintzas et al.1993;
Below et al. 1995; McConell et al. 1996;
Jeukendrup et al.1997). The increases in exercise
performance with CHO ingestion are believed
to be due to maintenance of a high rate of
CHO oxidation and increased CHO availability
within contracting skeletal muscle (Coyle et al.
1986; Coggan & Coyle 1987; Tsintzas et al.1996a).
In addition, the prevention of neuroglucopenia
and effects on central nervous system function
may play a role (Davis et al.1992). Interestingly,
several recent studies have observed improved
high-intensity and intermittent exercise perfor-
mance with CHO ingestion when, under normal
circumstances, CHO availability is not thought
to be limiting (Anantaraman et al.1995; Ball et al.
1995; Below et al.1995; Nicholas et al.1995; Davis
et al.1997; Jeukendrup et al.1997). The mecha-
nisms underlying the ergogenic benefit of CHO
ingestion under these circumstances remain to be
determined, but may involve small increases in
intramuscular CHO availability under condi-
tions of high CHO utilization. Performance in a
20-km cycle time trial, lasting about 30 min, was
not affected by CHO ingestion (Palmer et al.
1998).