Page 82 - Journal of Special Operations Medicine - Winter 2016

In addition to the effects of caffeine listed, caffeine can Other potential mechanism for enhanced physical per-
be addictive. Many caffeine users develop tolerance formance may be through caffeine actions on ryanodine
19
and experience withdrawal symptoms, which can lead (RyR) and adenosine receptors. The RyR1 receptor, a
to caffeine dependence. The debate about whether channel that controls calcium release and initiates con-
19
caffeine is an addictive substance is controversial and tractions in heart and skeletal muscle, is activated by
experts in psychology and pharmacology have differing caffeine; several studies have shown that caffeine en-
opinions. Often included in this consideration is whether hances force production during submaximal stimulation,
a person believes that (s)he cannot control or stop the which may reflect potentiating calcium release. 23,24 Thus,
use of caffeine. Despite these properties, most people do the performance-enhancing effects of caffeine may be
not consider caffeine a drug and regard it as socially ac- through enhanced calcium mobilization or stimulation
ceptable to use. In fact, caffeine is the most widely used of the CNS. Regardless of the mechanism, caffeine-re-
25
drug in the world that is known to alter behavior and, lated performance improvements depend on factors such
even in small doses, has marked effects on the central as the type of exercise, the condition of the athlete, the
nervous system (CNS). One of its well-known uses is for dose and timing of caffeine, the sensitivity of the person
performance enhancement. 9,20 to caffeine, nutritional patterns, genetics, and more.

Interestingly, improvements in physical performance
Caffeine and Performance
with caffeine have been noted primarily in trained ath-
The role of caffeine in enhancing performance has been letes and elite performers: caffeine does not appear to
studied for years. The wealth of this literature allows for improve performance in nonathletes or individuals who
an interesting distinction to be drawn between physi- are “out of shape.” With regard to amount of caffeine,
cal and cognitive performance. Table 1 provides a brief low to moderate, repeated doses of caffeine (~2–6mg/kg
overview of the state of the literature with regard to caf- body weight) every 2–3 hours effectively enhance per-
feine’s effects on specific aspects of physical and cogni- formance in trained athletes. 26-29 For military relevant
tive performance. performance (e.g., SEAL training), absolute doses of 200
and 300mg have shown to improve performance more
30
Table 1 Summary of Evidence for Performance-Enhancing effectively than 100mg. This distinction may indicate
Effects of Caffeine that absolute (100–300mg) rather than relative (2–6mg/
Not No kg body weight) amounts of caffeine are most important.
Physical Domain Enhanced Certain Evidence
Speed endurance X It is very important to note that the notion that caffeine
cycling/running is a strong diuretic and can contribute to dehydration is
Sprints X a myth. 31-33 Caffeine does not lead to excessive fluid loss
in healthy adults. A recent review by Zhang et al.
33
33
Anaerobic X concluded that concerns regarding fluid loss and poten-
performance tial adverse effects on fluid balance associated with caf-
Muscle force X feine ingestion were unfounded.
Agility X
Memory X Cognitive Performance
Attention SR X With the established effects of caffeine on physical
performance, it begs the question: Can/does caffeine
Executive function X enhance cognitive performance? The term cognition is
Perception SR used to refer to several brain functions, including per-
Vigilance ception, information processing, memory, attention,
SR, sleep restriction. and executive function. Current research on psycho-
stimulants suggests that caffeine may only indirectly af-
fect cognition. 2,34–36
Physical Performance
Caffeine has been shown to have ergogenic, or energy- These effects have been studied in the field and labora-
producing, effects for endurance, high-intensity inter- tory, usually under conditions of restricted sleep. For the
mittent activity over a prolonged duration, and, in some most part, any cognitive improvements after consuming
cases, strength-power performance. Although it was caffeine are most likely related to its indirect action on
generally concluded that endurance performance was arousal, mood, and vigilance/concentration. 2,34-36 Seidle
enhanced by changing how fuel was used during exer- and colleagues reported positive effects of caffeine on
37
cise (mobilizing fat and delaying depletion of glycogen), cognitive functions and mood, and other investigators re-
this notion is being disputed. 21,22 ported improvements in information-processing speed and

66 Journal of Special Operations Medicine Volume 16, Edition 4/Winter 2016