events at power outputs corresponding to
150–300% V
.
o2max.lasting less than 90 s. The
amount of energy derived from anaerobic
processes would be approximately 75–80% of the
total in the first 30 s, approximately 65–70% over
60 s and approximately 55–60% of the total
energy over 90 s.
Williams et al. (1988) reported that caffeine
ingestion had no effect on maximal power
output or muscular endurance during short,
maximal bouts of cycling. Collomp et al. (1992)
reported that 5 mg caffeine · kg–1did not increase
peak power or total work during a 30-s Wingate
test, but the same group later reported that 250
mg caffeine produced a 7% improvement in the
maximal power output generated during a series
of 6-s sprints at varying force–velocity relation-
ships (Anselme et al. 1992). The authors also
examined the effects of 4.3 mg caffeine · kg–1on
two 100-m freestyle swims, separated by 20 min
(Collompet al. 1990). In well-trained swimmers,
caffeine increased swim velocity by 2% and 4% in
the two sprints, but performance times were not
reported. Caffeine had no effect on sprint perfor-
mance in untrained swimmers.
Therefore, given the present information, it is
not possible to conclude whether caffeine has an
ergogenic effect on sprint performance. The brief
and intense nature of sprint exercise makes it
difficult to study and demonstrate significant
differences.
Field studies
Exercise performance in most laboratory studies
is measured as the time taken to reach exhaustion
at a given power output or the amount of work
that can be performed in a given amount of time.
However, in the field, performance is usually
measured as the time taken to complete a certain
distance. Consequently, extrapolations from
the laboratory to field settings may not be valid.
Occasionally, laboratory studies simulate race
conditions and other studies measure perfor-
mance in the field (track, swimming pool) in time
trial settings without actual race conditions.
However, these studies still do not simulate real
competitions. In field studies that do simulate
race conditions, it is often impossible to em-
ploy the controls required to generate conclusive
results. For example, Berglund and Hemmings-
son (1982) reported that caffeine increased cross-
country ski performance by 1–2.5 min with a
control race lasting 1–1.5 h. This improvement
occurred at altitude but not at sea level. Unfortu-
nately, the weather and snow conditions were
variable in both locations, requiring normali-
zation of the performance times in order to
compare results. A recent field study reported
that ingesting 0, 5 or 9 mg caffeine · kg–1had no
effect on 21-km road-race performance in hot
and humid environments (Cohen et al. 1996).
While subjects acted as their own controls, no
subjects received the placebo treatment in all
three races to assess whether between race envi-
ronmental differences affected race performance,
independent of caffeine.
The problems associated with field trials
raise questions about the validity of the results
and indicate how difficult it is to perform
well-controlled and meaningful field trials.
However, there is clearly a need for more field
studies.Theories of ergogenicity
The mechanisms that may contribute to the
ergogenic effects of caffeine are categorized
into three general theories. The first theory is
the classic or ‘metabolic’ explanation for the
ergogenic effects of caffeine during endurance
exercise involving an increase in fat oxidation
and reduction in CHO oxidation. The metabolic
category also includes factors which may affect
muscle metabolism and performance in a direct
manner, including inhibition of phosphodi-
esterase, leading to an elevated cyclic adenosine
monophosphate (AMP) concentration, and
direct effects on key enzymes such as glycogen
phosphorylase (PHOS). The second theory pro-
poses a direct effect of caffeine on skeletal muscle
performance via ion handling, including Na+–
K+-ATPase activity and Ca^2 +kinetics. The third
theory suggests that caffeine exerts a direct effect