causes severe muscle damage. O’Reilly et al.
(1987) reported that muscle glycogen stores
reduced by eccentric exercise were still signifi-
cantly below normal levels after 10 days of recov-
ery. Costill et al. (1990) also found that the rate of
muscle glycogen resynthesis was significantly
reduced following glycogen depletion by exer-
cise that incorporated a substantial eccentric
component, and that the reduced rate of resyn-
thesis was associated with muscle damage. More
recently, Asp et al. (1995) demonstrated that
muscle damage induced by eccentric exercise
resulted in a down regulation of GLUT-4 protein
that lasted for several days. In addition, it was
not until the GLUT-4 protein returned to the pre-
exercise concentration that normal muscle glyco-
gen levels were restored. These results suggest
that muscle damage following exercise can limit
glucose uptake due to a reduced GLUT-4 protein
concentration, and that this limits the restoration
of muscle glycogen.
Recommendations
From a dietary position, the first concern of the
endurance athlete is that energy consumption
and energy expenditure be in balance (Sherman
1995). The endurance athlete may expend 15–
30 MJ · day–1when training. If consumption is
inadequate and not balanced with expenditure,
the athlete’s training and competitive abilities
will eventually be adversely affected. It is also
important that a substantial percentage of the
diet consist of carbohydrate. It was suggested by
Sherman and Lamb (1988) that the endurance
athelete’s diet consists of approximately 65% car-
bohydrate during strenuous training. However,
this percentage can be modified according to
actual energy consumption. What is important is
the amount of carbohydrate consumed. Costill
et al. (1981) recommended that endurance
trained athletes consume approximately 8 g car-
bohydrate · kg–1body weight · day–1to maintain a
normal muscle glycogen concentration during
training. Similarly, a recommendation of 7 g
carbohydrate · kg–1body weight · day–1was pro-
vided by Sherman (1995).
108 nutrition and exercise
Prior to competition, the muscle and liver
glycogen stores should be maximized. For the
best results with the least amount of stress, it is
recommended that a hard training bout be per-
formed 7 days prior to competition to reduce the
muscle glycogen stores. During the next 3 days,
training should be of moderate intensity and
duration and a well-balanced mixed diet com-
posed of about 45–50% carbohydrate consumed.
During the next 3 days, training should be grad-
ually tapered and the carbohydrate content of
the diet should be increased to 70%. This should
result in muscle glycogen stores similar to that
normally produced by the classic glycogen
supercompensation regimen, but with much less
stress and fatigue.
For the rapid replenishment of muscle glyco-
gen stores, one should consume a carbohydrate
supplement in excess of 1 g · kg–1body weight
immediately after competition or after a training
bout. Continuation of supplementation every 2 h
will maintain a maximal rate of storage up to
6 h after exercise; smaller supplements taken
more frequently are also effective. Increasing
the amount of carbohydrate consumption
above 1.0–1.5 g · kg–1body weight · supplement–1
appears to provide no additional benefit, and
may have the adverse effects of causing nausea
and diarrhoea. Supplements composed of
glucose or glucose polymers are more effec-
tive for the replenishment of muscle glycogen
stores after exercise than supplements composed
of predominantly fructose. However, some
fructose is recommended because it is more effec-
tive than glucose in the replenishment of liver
glycogen. It might also be of benefit to include
some protein with the carbohydrate supplement
as this will enhance the rate of glycogen resyn-
thesis. Finally, carbohydrates in solid or liquid
form can be consumed immediately after exer-
cise with similar results. However, a liquid
supplement immediately after exercise is recom-
mended because it is easier to digest and less
filling, and therefore will not tend to adversely
affect one’s normal appetite. A liquid supple-
ment also provides a source of fluid for rapid
rehydration.