NUTRITION IN SPORT

experimental period to ensure that subjects
started with similar muscle glycogen levels. The
lower carbohydrate diet produced a significant
30% decline in muscle glycogen by day 5 of train-
ing, which was then maintained through day 7.
However, there was no decline in muscle glyco-
gen during the 7 days of training when the ath-
letes consumed the higher carbohydrate diet.

102 nutrition and exercise

The type of carbohydrate consumed also

appears to have an effect on the rate of glycogen

resynthesis following exercise. Costill et al. (1971)

fed glycogen-depleted runners a starch or

glucose diet (650 g carbohydrate · day–1) during

the 2 days following depletion. During the first

24 h there was no difference in the synthesis of

muscle glycogen between the two diets, but after

the 2nd day, the starch diet resulted in a sig-

nificantly greater glycogen synthesis than the

glucose diet. A difference in glycogen storage

between simple and complex carbohydrates,

however, was not demonstrated by Roberts et al.

(1988). Following glycogen-depleting exercise,

their subjects were fed diets consisting of either

88% simple and 12% complex carbohydrates or

15% simple and 85% complex carbohydrates.

After 3 days of recovery, it was found that the

two diets had produced equivalent increases in

muscle glycogen storage. The difference between

studies is not immediately clear, but may be due

to differences in the glycaemic indexes of the dif-

ferent carbohydrates provided.

The only study that appears to have investi-

gated the impact of the glycaemic index of car-

bohydrate on muscle glycogen storage after

220

165

110

55

0

01234 56

Regimen (days)

Glycogen

(μ

mol

.g

–1

wet wt)

Exercise

Exercise Exercise

Fig. 7.2A comparison of the classic Bergström et al. (1967) glycogen supercompensation method and a
modification of that method by Sherman et al. (1983). The classic method (—) consisted of depleting the glycogen
stores with an exhaustive exercise bout, followed by 3 days on a low carbohydrate diet. This was followed with
another glycogen-depleting exercise and 3 days on a high carbohydrate diet. The modifications by Sherman (- - - -)
included a hard exercise bout that was followed by 6 days of exercise tapering. During the first 3 days of the taper, a
mixed diet consisting of 50% carbohydrates was consumed. During the last 3 days, a high carbohydrate diet was
consumed. The two values for the classic regimen on day 3 represent before and after an exhaustive exercise bout.

, low carbohydrate diet; , mixed diet; , high carbohydrate diet. From Sherman et al. (1983), with permission.

80

60

40

20

0

–20

0 200 400 600

Consumed carbohydrate (g.day–1)

Glycogen storage

(μ

mol

.g

–1

wet wt

.h

–1

)

Fig. 7.3The relationship between the amount of
carbohydrate consumed and the rate of muscle
glycogen storage during a 24-h period after glycogen
depletion by exercise. From Costill et al. (1981), with
permission.