6-s maximal sprints on a cycle ergometer with
30 s of recovery between each sprint. The applied
load for the sprints was calculated as for the
WAnT protocol (75 g · kg–1body mass). Biopsies
were taken from the vastus lateralis muscle
before and after the first sprint and 10 s before
and immediately after the 10th sprint. Mean
power output generated over the first 6-s sprint
was sustained by an equal contribution from PCr
degradation and anaerobic glycolysis. By the end
of the first sprint, PCr and glycogen concentra-
tion decreased by 57% and 14%, respectively, of
resting values, and muscle lactate concentration
increased to 28.6 mmol · kg–1dry matter, an indi-
cation of significant glycolytic activity. However,
in the 10th sprint, mean power output was
reduced to 73% of that generated in the first
sprint, despite the fact that there was a dramatic
reduction in the energy yield from anaerobic gly-
colysis. Thus it was suggested that power output
during the last sprint was supported by energy
that was mainly derived from PCr degradation
and an increased aerobic metabolism.
Thus the weight of available evidence shows
that it is unlikely that sprinting is limited by
muscle glycogen availability, unless the glycogen
concentration falls below a critical threshold
value of 100 mmol · kg–1of dry matter. Glycogen
availability is also unlikely to limit peak power
output during repeated sprints because of the
decline in glycogenolysis and lactate production
observed under these conditions. However, as
reviewed in the next section, evidence shows that
an inadequate intake of carbohydrate in the diet
is detrimental to sprinting.
Carbohydrate intake and repeated
maximal sprints
An inadequate carbohydrate intake has been
shown to decrease performance during a second
maximal cycle ergometer interval test performed
2–3 days after the first test (Fulcher & Williams
1992; Jenkins et al. 1993). Fulcher and Williams
(1992) studied the effects of 2 days’ intake of
either a normal carbohydrate (450±225 g) or a
low carbohydrate (71±27 g) diet on power
output during maximal intermittent exercise.
Two trials were performed, one before, and then
one following the 2 days of dietary manipula-
tion. The test protocol comprised five sets of
five all-out fixed level sprints with 30 s recovery
(65 g · kg–1 applied load) separated by 5 min
active recovery. A final, sixth set comprised 10¥
6-s sprints, separated by 30 s recovery. Those sub-
jects who ate their normal amount of carbohy-
drate showed a significant improvement in peak
power output during the five sets of sprints in
test 2 compared with test 1. No such improve-
ment was shown in test 2 after the low carbohy-
drate diet. In the study by Jenkins and colleagues
(1993), 14 moderately trained individuals com-
pleted two intermittent exercise tests, separated
by 3 days. Each test comprised five bouts of 60-s
cycle performed maximally, with successive
exercise periods separated by 5 min of passive
recovery. During the 3-day period between trials,
each subject was randomly assigned to either a
high carbohydrate (83%), moderate carbohy-
drate (58%) or low carbohydrate (12%) diet.
Although performance declined in the low car-
bohydrate condition in both these studies, the
amount of carbohydrate ingested (10% and 12%,
respectively, of total energy intake) was signifi-
cantly lower than the amount normally con-
sumed by athletes. Nevertheless, these studies
highlight the importance of an adequate intake
of dietary carbohydrate for those individuals
performing repeated sprint exercise.
These results emphasize the need for sprinters
in training, and sportsmen and women compet-
ing in the multiple sprint sports (see Chapter 45
for a more detailed review) to consume adequate
amounts of carbohydrate on a daily basis. Much
research has been carried out to determine the
amount of carbohydrate needed to replenish
glycogen stores within 24 h of intense training.
A diet which comprised approximately 8–10 g
carbohydrate · kg–1 body mass was sufficient
to replace muscle glycogen stores after daily 1-h
training sessions (Pascoe et al. 1990). High-
intensity endurance capacity was also improved
following a high carbohydrate recovery diet
(Nicholaset al. 1997). However, some studies