Caffeine, Habituation, and Performance
It is standard procedure for a research protocol to
account for the daily caffeine intake of all subjects
included within a particular study. The purpose of
accounting for this type of dietary information is to
determine if caffeine consumption a.) has an effect on
performance and b.) if this outcome is different between
a person who does or does not consume caffeine on a
regular basis. In fact, as previously discussed in this
paper Bell and colleagues [41] examined the effect of a
moderate dose of caffeine on persons identified as users
(≥ 300 mg/d) and nonusers (≤ 50 mg/d). Results demonstrated
an enhancement in performance for both groups;
however, the treatment effect lasted approximately three
hours longer for those persons identified as nonusers
[41].
Dodd et al. [82] identified caffeine habituation
between subjects in a similar manner to Bell and colleagues
[41] and reported no statistical difference between
groups for VO2max (subjects participated in a graded
exercise protocol). The only reported differences, such
as ventilation and heart rate, were at rest for those persons
not habituated to caffeine [82]. Van Soeren et al.
[83] also reported no significant changes between users
and nonusers of caffeine, other than an increase in
plasma epinephrine during exercise for persons not
habituated to caffeine, as compared to placebo. Finally,
it was suggested by Wiles et al. [69] that daily caffeine
consumption among subjects did not have an effect on
the performance outcomes of that particular study,
which examined the effects of 3 g of coffee containing
approximately 150-200 mg of caffeine, on treadmill running
time.
What may be important to consider is how caffeine
affects users and nonusers individually. For example,
Astorino and colleagues [76] examined the effects of 6
mg/kg of caffeine on bench press one-repetition maximum.
Thirteen of 22 subjects in that investigation
described feelings of greater energy, elevated heart rate,
restlessness, and tremor. It should also be noted that
these feelings were enhanced in participants who consumed
little caffeine on a daily basis [76]. It would seem
the important factor to consider is the individual habits
of the athlete and how caffeine supplementation would
affect their personal ability to perform. In terms of practical
application, it is the responsibility of the coach
and/or athlete to determine what dose of caffeine, if
any, is suitable for competition.