with a high glycaemic index—those carbohy-
drates which result in a large and sustained ele-
vation of the blood glucose concentration after
ingestion—are the most effective when rapid
glycogen replacement is desired (Coyle 1991).
However, the nature in which carbohydrates
with a high or moderate glycaemic index are con-
sumed after exercise (i.e. as a solid or liquid)
appears to have no influence on glycogen syn-
thesis rates (Keizer et al. 1986; Reed et al. 1989).
Timing of carbohydrate intake
The muscle appears to have a particularly high
affinity for carbohydrate immediately after exer-
cise, and the greatest rate of muscle glycogen
resynthesis occurs over the first 2 h immediately
after exercise (i.e. 7–8 mmol · kg–1·h–1vs. the rate
after this time of 5–6 mmol · kg–1·h–1: Fig. 19.1)
(Ivyet al. 1998b). This increased synthesis rate
can only take place, however, if sufficient carbo-
hydrate is ingested and is available to the body.
Therefore, to optimize this transient increase
in maximal glycogen resynthesis rate, carbohy-
drate should be consumed as soon as possible
after exercise as this will allow the maximum
258 nutrition and exercise
advantage to be taken by allowing the increased
rate to be utilized for as long as possible. As a
guide, it is suggested that approximately 0.7 g
glucose · kg–1body mass should be consumed
every 2 h for the first 4–6 h after exercise in order
to maximize the rate of glycogen resynthesis
(Keizeret al. 1986; Blom et al. 1987). It does not
make any difference whether this carbohydrate
to be consumed is ingested as a few large meals
or as many small, frequent meals (Burke et al.
1996).Liver glycogen resynthesis
Liver glycogen restoration occurs less rapidly
than muscle glycogen restoration and indeed,
the fast repletion of muscle glycogen stores may
be at the expense of liver glycogen levels (Fell
et al. 1980). However, whereas fructose does not
promote as rapid a muscle glycogen restoration
as glucose, fructose infusion has been found to
give a greater liver glycogen resynthesis than
glucose (Nilsson & Hultman 1974). Some replen-
ishment of the liver glycogen stores may be pos-
sible by gluconeogenesis, but this will not be
sufficient to maintain carbohydrate homeostasis.
After very high intensity exercise, however, such
as multiple sprints in training, a substantial part
of the muscle glycogen that has been converted
to lactate by anaerobic glycolysis will be avail-
able as a substrate for hepatic gluconeogenesis.Postexercise fluid replacement
It has been pointed out elsewhere in this volume
that the athlete who begins exercise in a state of
hypohydration will be unable to achieve peak
performance and will also be at increased risk of
heat illness when the exercise is to be performed
in a warm environment. Where substantial sweat
losses have been incurred, it is therefore essential
that restoration of fluid and electrolyte balance
should be as rapid and complete as the circum-
stances allow. The opportunities for replacement
may be limited, as when several rounds of a tour-
nament are scheduled for a single day, or when
the time allowed between the weigh-in and com-Glycogen synthesis (μmol.g
–1
wet wt)20015100–1205120–240
Time after exercise (min)Fig. 19.1Muscle glycogen storage during the first 2 h
and second 2 h of recovery from exercise. The subjects
consumed 2 g glucose polymer · kg–1body mass (as a
23% solution) either immediately following exercise
( ) or 2 h after exercise (). Adapted from Ivy et al.
(1988b).