Introduction
Caffeine is a socially acceptable drug that is
widely consumed throughout the world. It is
also commonly used by athletes in their daily
lives and in preparation for athletic training
and competitions. Caffeine is a ‘controlled or
restricted drug’ in the athletic world. Urinary
caffeine levels greater than 12mg·ml–1 fol-
lowing competitions are considered illegal by
the International Olympic Committee (IOC).
However, most athletes who consume caf-
feine beverages prior to exercise would not
approach the illegal limit following a com-
petition. Therefore, if caffeine ingestion
enhances sports performance, it occupies a
unique position in the sports world. It is an
accepted component of the diet of many athletes,
although it has no nutritional value and would
be a ‘legal’ drug and ergogenic aid in these
situations.
Review articles in the early 1990s concluded
that the effects of caffeine ingestion on exercise
performance and metabolism were inconsistent
(Wilcox 1990; Conlee 1991). The authors stated
that many experiments had not been well
controlled and Conlee (1991) summarized the
factors which appeared to confound the caffeine
results: the exercise modality, exercise power
output, caffeine dose used in the experimental
design; the nutritional status, training status,
previous caffeine use of the subjects; and individ-
ual variation. An additional factor is the ability to
reliably measure exercise performance, which
improves with increased training frequency and
intensity.
Recent research has attempted to control these
factors and has demonstrated an ergogenic effect
of caffeine during prolonged endurance exercise
(>40 min). Investigations examining the effects
of caffeine on exercise performance during
intense exercise lasting approximately 20 min
and shorter durations (ª4–7 min) and sprinting
(<90 s) have also appeared. At this point it is diffi-
cult to conclude whether caffeine is ergogenic
during exercise lasting less than 20 min (for
review, see Spriet 1997).
Caffeine appears to be taken up by all tissues
of the body, making it difficult to independently
study its effects on the central nervous
system (CNS) and the peripheral tissues (skeletal
muscle, liver and adipose tissue) in the exercis-
ing human. It is also likely that multiple and/or
different mechanisms may be responsible for
performance enhancement in different types of
exercise.
This chapter provides a brief but comprehen-
sive review of the issues surrounding caffeine’s
ability to enhance exercise performance in
humans and the mechanisms which may explain
the ergogenic effects. The chapter does not
contain a complete list of citations but highlights
current thinking in the caffeine area and indi-
cates where information is lacking.