Will Caffeine Work as an Erqoqenic Aid?
The Latest Research
BRENT C. MANGUS, EdD, ATC • University of Nevada Las Vegas
CYNTHIA A. TROWBRIDGE, PhD, ATC, CSCS, LAT • University of Texas at Arlington
.thletes at all levels of participation often
search for methods to enhance performance.
Doing so through training techniques, psychological strategies, nutritional practices,
and ergogenic aids
such as legal and illegal
KEY POINTS
pharmaceutical agents
is becoming more
Athletes in a variety of sports are using
common.
Certified
caffeine as an ergogenic aid.
athletic trainers (ATCs)
need to be knowledgeThe IOC and USOC no longer ban its use In
competitions, but the NCAA continues to
able about the constant
restrict caffeine use by athletes.
evolution of ergogenic
aids available to athThere are three theories of how caffeine
letes. Therefore, the
provides an ergogenic benefit to athletes.
professional literature
should provide regular
Athletic trainers need to be able to educate
updates of completed
athletes about the ergogenic and adverse
research on specific
effects of caffeine.
ergogenic aids so that
ATCs can help educate
Key Words: sport supplements, endurance
coaches and athletes.
exercise, drug testing, athlete education
Many ergogenic aids
can be used safely in a
training program, but there are tragic stories of athlete disqualification or death from
the use of banned or potentially dangerous
supplements.'
The purpose of this article to provide
a brief overview of caffeine as it relates to
improving athletic performance. We reviewed
the scientific literature published over the
past 25 years to investigate the ergogenic
effectiveness of caffeine, to determine the
potential risks associated with caffeine use,
and to provide ATCs with helpful tips for
counseling athletes about caffeine use.
Currently, there are three theories as to
caffeine is helpful to athletes. Although
some of the more recent theories conflict
with earlier published reports, ATCs should
have a basic understanding of all these theories. After reading this article, ATCs will be
better able to draw their own informed conclusions concerning caffeine as an ergogenic
aid and will be better able to educate coaches
and athletes.
Caffeine
Caffeine belongs to the xanthine class of
drugs, which act as stimulants for the cardiovascular, muscular, and central nervous
systems.^ Caffeine acts directly on tissues
or secondarily by stimulating the release
of catecholamines such as epinephrine,
which produces a stimulatory effect.' Commonly found in soft drinks, coffee, tea, and
chocolate, caffeine can also be found in cold
medications and pain relievers." It is almost
100% bioavailable on ingestion, and bloodplasma concentrations peak 15-45 min after
oral ingestion. In nonexercising adults, the
half-life of caffeine has been measured to be
from 2 to 15 hr, depending on the individual's
metabolism.^
Traditionally, coffee has been the major
source of caffeine because it is easy to obtain
and socially accepted in almost every country
and culture. The amount of caffeine in coffee
varies, however, based on the preparation
technique. There are many other chemicals
besides caffeine in coffee, but caffeine is the
most widely recognized and studied component. In the late 1970s, caffeinated coffee was
documented to have an ergogenic benefit for
endurance athletes.^'^ Because of caffeine's
documented performance-enhancement
© zoos Huttiati Kittetics - ATT 10(3), pp. 57-6Z
ATHLETIC THERAPY TODAY
MAY 2 0 0 5
157
effect, over-the-counter (OTC) and prescription medications, as well as many beverages, include caffeine as
an ingredient. Examples of OTC medications include
NoDoz®, Vivarin®, and various "diet pills," and the beverages include products such as Jolt® cola. Red Devil®,
Red Bull®, Water Joe®, Bawls®, and Mountain Dew®.
Theories
Much of the early caffeine research was conducted
at Ball State University by Costill.^'^ In the mid 1970s,
Costill and colleagues studied the effect of caffeine
using bicycle ergometry and documented up to a 20 %
increase in the time a trained athlete could cycle to
exhaustion. The researchers believed that caffeine,
through one or more metabolic processes, produced
a glycogen-sparing effect and concluded that it was
mobilizing adipose stores. Adipose mobilization
increases free-fatty-acid blood concentration, potentially sparing glycogen by allowing free fatty acids to
become a more available source of energy.
A second theory, sometimes referred to as the masking effect, has a more recent origination. According to
this theory, the central nervous system is stimulated
and does not allow the brain to sense the fatigue associated with exhaustive exercise.^'" Because caffeine has
a chemical structure similar to that of adenosine, it
binds to adenosine receptors in the brain. It produces
the opposite effect of adenosine, however, resulting in
vasoconstriction, decreased blood flow, and centralnervous-system stimulation." Therefore, an athlete
can continue to exercise because the brain does not
process the message that the body is fatigued. Kalmar
and Cafarelli,'^ who studied the effect of caffeine on
maximum voluntary muscle contraction, demonstrated
a specific example of this theory. Muscle activation
during a maximal voluntary contraction increased
by 3.5%, but there was no change in the H-reflex
amplitude.'^ They concluded that caffeine increased
voluntary activation by blocking adenosine receptors
at the supraspinal level, which allows for greater and
more efficient motor-unit excitation.
A third theory, developed by Tarnopolsky and
Cupido," suggests that the muscle cell is the direct
benefactor of the caffeine. Ingesting caffeine before
activity allows the sarcoplasmic reticulum in the
muscle cell to release more calcium, which facilitates
prolonged muscle contraction.''" The muscle is able to
58 1 MAY 2 0 0 5
sustain the output of force for a longer period because
of the additional calcium, which is required for actin/
myosin cross-bridge formation.
There is still no universally accepted theory explaining the beneficial ergogenic effect of caffeine. Even the
most recent published reports do not provide a specific
explanation for the peripheral or central mechanisms
responsible for its ergogenic effect.'"'* Therefore,
an athlete's response to caffeine ingestion seems to
be individual, and the ergogenic benefit each person
obtains is variable.
Application to ATCs
ATCs should be prepared to talk with athletes about
caffeine as an ergogenic aid. Some of the questions
athletes might pose include. How much do I need to use
to obtain a beneficial effect? Will caffeine cause diuresis
and dehydration? Will caffeine be helpful to endurance
or high-intensity exercise? What effect does being a
habitual caffeine user have on the overall effectiveness
of caffeine in performance enhancement? How much
can I use before I will test positive with the NCAA or
some other governing body? and What are the adverse
effects of using caffeine to perform better?
How Much Do I Need?
An endurance athlete does not have to take high doses
of caffeine to gain an ergogenic effect.'^ Even relatively
small amounts of caffeine can improve an endurance
athlete's performance. As little as 3-5 mg/kg appears
to provide an ergogenic effect for endurance performance.'^ For a 150-lb athlete, this is equivalent to
225-375 mg of caffeine. Two cups of brewed coffee,
two Red Bull drinks, or two Vivarin pills might suffice
(Table 1). The quickest way to increase the caffeine level
is by ingesting coffee or by taking one of the caffeinated
OTC products promoted for weight loss or antifatigue
purposes. Caffeine tablets taken with water produce a
greater ergogenic effect than the caffeine in coffee or
drinking decaffeinated coffee with caffeine tablets."
Will Caffeine Cause Diuresis and Dehydration?
Caffeine can cause moderate diuresis at rest and predispose an athlete to mild dehydration.2°-2' Ingesting
moderate amounts of caffeine (< 6 cups of coffee)
during prolonged exercise, however, does not significantly increase diuresis, because of exercise-induced
ATHLETIC THERAPY TODAY
TABLE 1. CAFFEINE CONTENT AND URINARY CONCENTRATION
OF COMMONLY U S E D FOODS, BEVERAGES, AND MEDICATIONS
Urinary Concentration
Substance
Coffee
8 oz drip brewed
8 oz Starbucks®
16 oz Starbucks
8 oz instant
8 oz decaffeinated
Tea
5 oz brewed for 1 min
5 oz brewed for 5 min
12 oz iced tea
Soft Drinks
12 oz Coca-Cola®
12 oz Dr. Pepper®
12 oz Pepsi®
12 oz Mountain Dew®
12 oz Jolt®
12 oz Red Bull®
Chocolate
1 oz milk chocolate
1 oz bittersweet chocolate
1 oz baking chocolate
OTC medications
1 NoDoz®
1 Vivarin®
1 Anacin®
1 Excedrin®
1 Midol®
1 Enerjets® lozenge
1 Dexatrim®
1 Aqua-Ban®
Caffeine Content (mq)
After 2-3 hr(|ji9/ml)
100-150
1.50-2.25
3.75
8.25
0.60-1.50
0.03-0.04
250
550
40-100
2-3
10-30
20-100
10-30
46
40
36
55
90
115
0.68
0.59
0.54
0.85
1.35
1.73
6
20
26
0.08
0.30
0.40
100
200
32
65
32
75
200
200
1.50
3.00
0.48
0.97
0.48
1.12
3.00
3.00
and epinephrine-stimulated renal vasoconstriction
and decreased glomerular filtration."'^^ Exercise
shifts blood to the working muscles and away from
the kidneys. Because there is less blood filtering
through the kidneys, the diuretic effect of caffeine is
reduced during exercise.^ Perspiration and respiration
account for most fluid loss during exercise. If fluid is
inadequately replaced, dehydration can result. Athletes should be concerned about consuming enough
fluids during exercise but do not necessarily have to
ATHLETIC THERAPY TODAY
0.15-0.45
0.30-1.50
0.15-0.45
increase fluid intake if using caffeine for its ergogenic
effect.
Prolonged Endurance vs. Intense Exercise
There is ongoing controversy concerning caffeine's
ergogenic effects. Pasman et al.'^ demonstrated that
endurance cycling performances with various levels
of caffeine ingestion (5, 9, and 13 mg/kg) were all
significantly better than in a placebo condition. Support for significant ergogenic benefits during intense
MAY 2 0 0 5 1 5 9
exercise has also been reported.'*'^'-^'' It has been demonstrated that 5mg/kg of caffeine during cycling at
85-90% maximal capacity can produce an ergogenic
effect.'^•^^•^'' Recent research, however, suggests that
caffeine does not provide an ergogenic effect to athletes participating in very short-duration, high-intensity
exercise bouts. Greer et al.^^ concluded that caffeine did
not improve peak power or the rate of power production during a Wingate cycle test. Therefore, caffeine
appears to be ergogenic for prolonged and intense
exercise but not for very short-duration, high-intensity
efforts.^'^''^'s-^-^s
Habitual Caffeine User vs. Competition-Only User
Experiments on infrequent users and athletes who
abstain from caffeine intake have been a focus of
research."'"^'^^'^^ Historically, experts have believed
that habitual caffeine users would not gain as much
ergogenic benefit during their performance because
there would not be as much epinephrine stimulation.
Increased epinephrine levels are not necessary for
caffeine to induce an ergogenic effect, however." It
now appears that even habitual users' muscle performance and fat oxidation can be improved via caffeine
even though the epinephrine response decreases with
chronic use.'^•'"•2* Short-term withdrawal by habitual
users has no effect on caffeine-induced increases in
endurance performance when compared with no withdrawal. Thus, habitual caffeine use does not seem to
detract from the ergogenic effect on endurance athletes' performance.^^
Testing Positive
Currently, only the National Collegiate Athletic Association (NCAA) officially classifies caffeine as a restricted
substance. Previously, the International Olympic Committee and the United States Olympic Committee had
caffeine on a banned-substance list but now do not test
for caffeine levels in urine. Only a few high schools
require athletes to be drug tested.^^ Drug testing can
be cost-prohibitive for many organizations, and most
American professional sports organizations do not test
for caffeine. The NCAA set a limit of 15 |xg/ml to indicate excessive levels of caffeine.^ Testing is performed
by measuring caffeine metabolites in the urine. The
level of caffeine established for disqualification from an
NCAA event would be produced by ingesting approximately 800 mg of caffeine before competition, which
6 0 1 MAY 2 0 0 5
corresponds to 6-8 cups of brewed coffee, seven Red
Bull drinks, or four Vivarin tablets (Table 1).
The amount of caffeine metabolites in an athlete's
urine does not provide any evidence of a performanceenhancing effect. Each individual metabolizes caffeine
at a different rate depending on age, gender, and lean
body mass.^ Depending on an individual athlete's genetic
makeup, it might take more or less caffeine to produce a
given urine concentration of metabolites. Research has
shown that as little as 3-5 mg/kg is effective in performance enhancement. '* To reach a urinary level of at least
12 |xg/ml an athlete would probably need to consume
between 8 and 15 mg/kg, so an athlete could obtain
ergogenic benefits without testing positive. Caffeine is a
flow-limited drug, meaning that its excretion decreases
as circulation is diverted from the kidneys to the muscles
during prolonged exercise. Thus, an athlete's urine metabolite concentration might not represent actual caffeine
use, because detection is confounded by the reduction
in urine volume. If an athlete is able to consume small
amounts of caffeine for ergogenic benefit without detection, he or she must reconcile the ethical implications.
Adverse Effects
There are health concerns regarding the overuse of
caffeine by athletes. Some of those concerns include
tachycardia during exercise,^'' increased blood pressure
in normal and mildly hypertensive individuals,'' •^° gastrointestinal distress,^' and addiction." During strenuous exercise the heart rate is increased because of
the requirements of the exercising muscles. Adding
caffeine-induced central-nervous-system stimulation
to the increase in heart rate from exercise can result
in negative cardiac effects during strenuous exercise.^^
Caffeine can cause nausea, gastrointestinal distress,
and diarrhea, which can cause a loss of fluids.^' Caffeine use can also result in the development of tolerance or addiction. When caffeine use is discontinued
abruptly, withdrawal symptoms such as headache,
fatigue, lethargy, and flu-like symptoms can result in
poor athletic performance." Many of these physical
symptoms might be related to the antagonist effect
that caffeine has on adenosine receptors.^'
Combined With Ma Huanq
Ma huang, the herbal form of the drug ephedrine, is
obtained from the ephedra plant.^"^ It is a sympathomi-
ATHLETIC THERAPY TODAY
metic drug that produces effects similar to the stimulation of the sympathetic nervous system. Ephedra is
now banned from saie in the United States but is still
widely available via illegal sources. It is a powerful
stimulant that is present in various products designed
to facilitate weight loss and maintain alertness. Similar
to caffeine, it increases heart rate, increases blood pressure, raises metabolism, and increases alertness.^^'^^
Ephedra increases the risi^ of heart attack, stroke,
seizures, and death.''' When combined with caffeine
and exercise, the side effects of ephedra become more
important to monitor in athletes. The combination can
significantly increase blood pressure and heart rate,
which can ultimately result in cardiac infarction.' In a
study by Jacobs et al.,'^ ingesting caffeine and ephedrine before exercise increased the mean systolic blood
pressure in 13 individuals to 156 + 29 mgHg.
Another concern for athletes is the proper labeling
of products containing ephedra. Athletes should be
cautioned that the Food and Drug Administration does
not currently monitor or enforce accurate labeling of
nutritional supplements. Therefore, athletes should be
wary of any products marketed to increase energy or
delay fatigue.
Cducatinq and Counseling Athletes
To recognize them as reliable advisors, athletes must
trust ATCs to provide them with factual information.
Following are guidelines for advising athletes about caffeine: First, caffeine does have ergogenic properties but
it can produce adverse effects, as well. Athletes should
understand that caffeine appears to improve endurance capacity for prolonged and intense activities but
is not effective for very short-duration, high-intensity
activities. Increased blood pressure, nausea, gastrointestinal discomfort, cardiac stimulation, tremors, and
diuresis are all potential complications from caffeine
use. There is also the potential for addiction and the
associated withdrawal symptoms. Second, if athletes
choose to use caffeine for its ergogenic properties they
should use it under a variety of training conditions.
Athletes should never try anything new on the day of
competition. Finally, athletes need to be warned and
be ready to accept the consequences of positive test
results for caffeine. Because it is a restricted drug, event
disqualification and scholarship revocation could result
from its use. Each individual must consider the ethical
ramifications of caffeine use for ergogenic benefit.
ATHLETIC THERAPY TODAY
Summary
Most published research from the past 25 years supports the premise that caffeine can have a beneficial
ergogenic effect on endurance performance in both
male and female athletes.''' There appears to be a
combination of events that might lead to this ergogenic effect, including effects on the cardiovascular,
metabolic, and central nervous systems.^••''•'^ It is not
clearly understood whether caffeine increases fat oxidation, alters calcium activity in the muscle cells, or
masks the perception of fatigue. Possibly, all of these
actions occur simultaneously. Caffeine capsules appear
more effective than drinking coffee or other highly caffeinated beverages.'^ Caffeine can be detected in the
urine, and the NCAA restricts levels of caffeine above
15 |xg/ml. This high threshold makes it difficult for an
athlete to consume enough coffee, other caffeinated
beverages, or medications before a competition to test
positive. There are health concerns, however, even with
low doses of caffeine. Each athlete should carefully
consider the advantages and disadvantages of a high
level of caffeine ingestion before competition. I
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Brent Mangus is an associate professor of athletic training in the
Department of Kinesiology and program director for the undergraduate athletic training curriculum. He has been a certified athletic trainer
for 26 years.
Cindy Trowbridge is an assistant professor of athletic training in the
Department of Kinesiology and clinical coordinator for the undergraduate athletic training program at the University of Texas at Arlington.
She has been a certified athletic trainer for 12 years.
ATHLETIC THERAPY TODAY