been caught with illegal levels during competi-
tions, although formal reports of the frequency of
caffeine abuse are rare. One study reported that
26/775 cyclists had illegal urinary caffeine levels
when tested following competition (Delbecke &
Debachere 1984).
Urinary caffeine and doping
The use of urinary caffeine levels to determine
caffeine abuse in sport has been criticized
(Duthel et al. 1991). Only 0.5–3% of orally
ingested caffeine actually reaches the urine as the
majority is metabolized in the liver. The excreted
caffeine by-products are not measured in doping
tests. Other factors also affect the amount of caf-
feine that reaches the urine, including body
weight, gender and hydration status of the
athlete. The time elapsed between caffeine inges-
tion and urine collection is also important and
affected by the exercise duration and environ-
mental conditions. Sport governing bodies may
not regard these concerns as problems since most
people caught with illegal levels of caffeine
will have used the drug in a doping manner.
However, it is possible that someone who metab-
olizes caffeine slowly or who excretes 3% of the
ingested dose rather than 0.5% could have illegal
urine levels following a moderate dose.
Habitual caffeine consumption
An athlete’s normal caffeine intake habits may
affect whether acute caffeine ingestion improves
performance. Many investigators ask users to
refrain from caffeine consumption for 2–3 days
prior to experiments. Caffeine metabolism is not
increased by use, but the effects of caffeine may
be altered by habitual use via alterations in
adenosine receptor populations. As reviewed by
Grahamet al. (1994), several studies suggest that
chronic caffeine use dampens the adrenaline
response to exercise and caffeine, but does not
affect plasma FFA concentration or exercise
RER (Bangsbo et al. 1992; Van Soeren et al.
1993). However, these changes do not appear to
dampen the ergogenic effect of 9 mg caffeine ·
kg–1. Endurance performance increased in all
subjects when both caffeine users and non-users
were examined and users abstained from caf-
feine for 48–72 h prior to experiments (Graham &
Spriet 1991; Spriet et al. 1992). However, the per-
formance results were more variable in a subse-
quent study with more non-users (Graham &
Spriet 1995). In addition, Van Soeren and
Graham (1998) reported no effect of up to 4 days
of caffeine withdrawal on exercise hormonal
and metabolic responses to doses of 6 or 9 mg
caffeine · kg–1 in recreational cyclists. Time to
exhaustion at 80–85% V.
o2max.improved with
caffeine and was unaffected by 0–4 days of
withdrawal.Caffeine and high carbohydrate diets
An early investigation suggested that a high
CHO diet and a prerace CHO meal negated the
expected increase in plasma FFA concentration
following caffeine ingestion during 2 h of exer-
cise at approximately 75% V.
o2max.(Weir et al.
1987). These results implied that high CHO
diets negated the ergogenic effects of caffeine,
although performance was not measured.
However, a high CHO diet and a pretrial CHO
meal did not prevent caffeine-induced increases
in performance in a number of recent studies
using well-trained/recreational runners and
cyclists (Spriet 1995).Diuretic effect of caffeine
Because caffeine is a diuretic, it has been sug-
gested that caffeine ingestion may lead to poor
hydration status prior to and during exercise.
However, no changes in core temperature, sweat
loss or plasma volume were reported during
exercise following caffeine ingestion (Gordon
et al. 1982; Falk et al. 1990). It has also been
demonstrated that urine flow rate, decreases in
plasma volume, sweat rate and heart rate were
unaffected by caffeine (ª600 mg), ingested in a
CHO electrolyte drink (ª2.5 l) during 1 h at rest
and 3 h of cycling at 60% V.
o2max.(Wemple et al.
1997).