to increased fat oxidation and decreased carbo-
hydrate (CHO) oxidation, as CHO availability
does not limit performance in this type of
exercise.
Graded exercise tests: 8–20 min
Several studies reported no effect of moderate
doses of caffeine on time to exhaustion and
V
.
o2max.during graded exercise protocols lasting
8–20 min (Dodd et al. 1993). However, two
studies reported prolonged exercise times when
doses of 10–15 mg caffeine · kg–1 were given
(McNaughton 1987; Flinn et al. 1990). Unfortu-
nately, no mechanistic information presently
exists to explain how these high caffeine doses
prolong exercise time during a graded test,
although it might be predicted that central effects
would be the most likely cause.
Intense aerobic exercise: ª20–40 min
Competitive races lasting approximately 20–40
min require athletes to exercise at power outputs
of approximately 80–95% V
.
o2max.. Caffeine
(6 mg · kg–1) significantly reduced 1500-m swim
trial time, from 21:22 (±38 s) to 20:59 (±36 s)
(min:s), in trained distance swimmers (MacIn-
tosh & Wright 1995). The authors reported lower
pre-exercise venous plasma [K+] and higher post-
exercise venous blood glucose concentration
with caffeine and suggested that electrolyte
balance and exogenous glucose availability may
be related to caffeine’s ergogenic effect. A second
study reported no ergogenic effect of caffeine in
mildly trained military recruits when cycling to
exhaustion (26–27 min) at approximately 80%
V
.
o2max.at sea level (Fulco et al. 1994). However,
cycle time was improved upon acute (35 vs. 23
min) and chronic (39 vs. 31 min) exposure to
altitude.
Intense aerobic exercise: ª4–7 min
Exercise events at high power outputs (ª100–
110% V
.
o2max.) that last for approximately 4–7 min
require near-maximal or maximal rates of energy
382 nutrition and exercise
provision from both aerobic and anaerobic
sources.
Collompet al. (1991) reported that moderate
caffeine doses increased cycle time to exhaustion
at 100% V.
o2max., from 5:20 with placebo to 5:49 in
one group and 5:40 in a second group, although
the increases were not statistically significant.
Wiles et al. (1992) reported that coffee ingestion (ª
150–200 mg caffeine) improved 1500-m race time
on a treadmill by 4.2 s over placebo (4:46.0 vs.
4:50.2). The runners in this study were well-
trained, but clearly not elite. In a second experi-
ment, subjects consumed coffee or placebo and
then ran for 1100 m at a predetermined pace, fol-
lowed by a final 400 m where they ran as fast as
possible. The time to complete the final 400 m
was 61.25 s with coffee and 62.88 s without. Fol-
lowing coffee, all subjects ran faster and the
meanV.
o2max.during the final 400 m was higher.
To document such small changes, the average
response to three trials in the caffeine and
placebo conditions was determined in both
experiments.
Jackmanet al. (1996) examined the effects of
caffeine ingestion (6 mg · kg–1) on the perfor-
mance and metabolic responses to three bouts of
cycling at 100% V.
o2max.. Bouts 1 and 2 lasted 2
min and bout 3 was to exhaustion, with rest
periods of 6 min between bouts. Time to exhaus-
tion in bout 3 was improved with caffeine (4.93±
0.60 min vs. placebo, 4.12±0.36 min; n=14).
Muscle and blood lactate measurements sug-
gested a higher production of lactate in the
caffeine trial, even in bouts 1 and 2, when power
output was fixed. The glycogenolytic rate was
not different during bouts 1 and 2 and less than
50% of the muscle glycogen store was used in
either trial during the protocol. The authors
concluded that the ergogenic effect of caffeine
during short-term intense exercise was not asso-
ciated with glycogen sparing and may be caused
by either a direct action on the muscle or altered
CNS function.Sprint exercise
Sprinting is defined as exercise or sporting