NUTRITION IN SPORT

exercise was conducted by Burke et al. (1993).
Subjects were exercised to deplete the muscle
glycogen stores on two separate occasions and
provided a diet composed of carbohydrate with
a high glycaemic index on one occasion, and a
diet composed of carbohydrate with a low
glycaemic index on the other. Total carbohy-
drate intake over the 24-h recovery period
was 10 g · kg–1body weight, evenly distributed
between meals eaten at 0, 4, 8 and 21 h after exer-
cise. The increase in muscle glycogen averaged
106 mmol·g–1wet weight for the high glycaemic
index carbohydrate and 71.5mmol · g–1 wet
weight for the low glycaemic index. The differ-
ence in glycogen storage was significant. This
finding suggests that the increase in muscle
glycogen content during long-term recovery is
affected by the amount and glycaemic index of
the carbohydrate consumed.

Short-term recovery

While procedures for increasing muscle glyco-
gen above normal levels in preparation for com-
petition and maintaining normal glycogen levels
on a day-to-day basis have been defined, these
procedures do not address the problem of
athletic competitions that require the rapid
resynthesis of muscle glycogen within hours.
Although it is unlikely that muscle glycogen
stores could be completely resynthesized within
a few hours by nutritional supplementation
alone, it would be of benefit to the athlete if sup-
plementation procedures which maximized the
rate of muscle glycogen storage after exercise
were defined. Factors that influence the rate of
muscle glycogen storage immediately following
exercise are the timing, amount and type of car-
bohydrate supplement consumed, the frequency
of feeding, and the type of exercise performed.

timing of carbohydrate
consumption after exercise

The time elapsed between competition or a pro-
longed exercise bout and the consumption of a
carbohydrate supplement will critically influ-
ence the rate of muscle glycogen resynthesis (Ivy

et al. 1988a). When carbohydrate supplements

are provided immediately after exercise, they

generally result in a rate of glycogen resynthesis

of between 5 and 6mmol · g–1wet weight · h–1

(Maehlumet al.1977; Blom et al.1987; Ivy et al.

1988a, 1988b). This rate is maintained for approx-

imately 2 h and then declines by approximately

50% over the next 2 h as the blood glucose and

insulin levels decline to after-exercise levels (Ivy

et al.1988a). If the supplement is delayed for 2 h,

the rate of glycogen resynthesis during the 2 h

immediately after consumption ranges between

3 and 4mmol · g–1wet weight · h–1, or about 50% as

fast as when the supplement is provided imme-

diately after exercise (Fig. 7.4). This lower rate

of glycogen resynthesis occurs despite normal

increases in blood glucose and insulin levels. It

appears that when the carbohydrate supplement

is delayed for several hours after exercise, the

muscle becomes insulin resistant, reducing the

rate of muscle glucose uptake and glycogen

optimization of glycogen stores 103

Fig. 7.4Muscle glycogen storage during the first 2 h

and second 2 h of recovery from exercise. The open bar

represents the glycogen storage when the

carbohydrate supplement was provided immediately

after exercise, and the black bar represents the

glycogen storage when the supplement was delayed

until 2 h into recovery. The carbohydrate supplement

consisted of a 23% solution of glucose polymers

(2 g · kg–1body weight). From Ivy et al. (1988a), with

permission.

Glycogen synthesis (

μmol

.g

–1

wet wt)

20

0

15

10

0–120

5

120–240

Time after exercise (min)