Ergogenic Espresso: The Performance Benefits of Caffeine
Caffeine is, by far, the most consumed drug in the world. Millions and millions of
people yearn for their daily dose to give them some quick energy, and it certainly
delivers. Improved mood, increased alertness and delayed fatigue are just some of its farreaching effects, and with only mild side effects (slight increases in heart rate and blood
pressure). Athletes began to take notice of these effects and the potential for performance
enhancement, and researchers were soon to follow. We now have plenty of studies
looking at caffeine as an ergogenic aid…whether it works, possible mechanisms and the
conditions that are ideal in order to optimize performance. This article will provide a
brief overview of caffeine, its effects on the body and some of the research done on
endurance athletes. I think you’ll be surprised and encouraged by the results!!
The Skinny on Caffeine
Caffeine (trimethylxanthine) is a xanthine alkaloid that is classified as a central
nervous system stimulant. It is found naturally in about 60 different plants, including
coffee, tea, kola nut, guarana, mate and cocoa. Caffeine is digested rapidly and absorbed
through the small intestine, ultimately ending up in the liver to be metabolized by the
Cytochrome P450 enzyme system. Here it is broken down into three separate
dimethylxanthines: paraxanthine, which increases fat breakdown; theobromine, which
dilates blood vessels and increases urine output; and theophylline, which relaxes smooth
muscle within the bronchial tubes. These byproducts are further metabolized prior to
urinary excretion. The half-life of caffeine is approximately six hours, though this varies
depending on the person and circumstances. This essentially means that half of a given
caffeine dose is still active in the body six hours after ingestion.
Caffeine has many mechanisms of action, but most of these stem from its role as
an adenosine receptor antagonist. Since it competes with adenosine, adenosine activity
gradually declines, leading to a concomitant increase in dopamine activity. This
dopamine effect provides caffeine with strong stimulatory actions within the body.
Caffeine also increases epinephrine (adrenaline), which leads to a cascade of events via
the sympathetic nervous system, including, but not limited to, increased heart rate,
increased shunting of blood to muscle tissue and increased blood pressure. It also
increases serotonin levels in the brain, resulting in positive mood changes. Other
metabolic effects include enhanced muscular contraction, increased glycogen breakdown
and increased free fatty acid release from adipose tissue. Keep in mind, we are only
scratching the surface in terms of the metabolic, physiological and psychological effects
caffeine has on the body. Graham et al summed up caffeine’s effects in one of their
reviews (1). They agreed that although adenosine receptor antagonism is the most widely
supported mechanism of action, it couldn’t explain all of the observed responses within
the body.
Does Caffeine Affect Endurance Performance?
We can say without a doubt that caffeine does improve performance in endurance
events, such as running and cycling. Costill and colleagues were the first to study caffeine
and its potential in endurance activities. In one of their studies, nine cyclists exercised to
exhaustion at 80% VO2 max after consuming either decaffeinated coffee or coffee
containing 330mg of caffeine 60 minutes prior to the start. The cyclists receiving the
caffeine were able to perform for 90 minutes, while those receiving the decaf only rode
for 75.5 minutes. This is significant because these were competitive cyclists, and a 15minute difference in an actual event would be nothing short of miraculous.
Graham and Spriet obtained similar results when they evaluated the effect of a
high caffeine dose during prolonged exercise (3). Seven competitive runners performed 4
exercise trials (two running and two cycling) at 85% VO2 max to exhaustion. Subjects
consumed either dextrose or caffeine at a dose of 9mg/kg body weight one hour before
exercise. Run times increased from 49 minutes in the placebo group to 71 minutes in the
caffeine group, and cycling times improved from 39 minutes to 59 minutes when caffeine
was used. Again, these results are very impressive, though we don’t exactly know how
applicable they are to a real world situation. It certainly is cause for excitement, and is
one reason that the International Olympic Committee banned caffeine prior to the 1972
Olympics and again from 1984 to 2004. Because of its persistent use throughout the
world, caffeine now sits on the monitored list, which means it is no longer banned from
competition.
How Does Caffeine Improve Performance?
It’s clear that caffeine improves endurance performance, but the real question is how does
it work? What mechanisms are at play that allow for these improvements? In Costill’s
study, he found that fat oxidation was significantly higher in the caffeine group, which
makes sense because we know that caffeine raises serum free fatty acid levels. Any
increase in fat oxidation might spare muscle glycogen for more intense cycling later on,
thereby improving endurance. He also found that perceived exertion ratings were much
lower in the caffeine group, meaning that the cyclists thought the exercise task was much
easier when ingesting the caffeine.
Graham and Spriet were able to show a glycogen-sparing effect in a study that
involved eight subjects cycling at 80% VO2 max to exhaustion (4). The subjects
consumed either dextrose or caffeine one hour before the start at a dose of 9mg/kg body
weight. Again, performance was substantially improved when using caffeine, and they
found that muscle glycogenolysis was decreased by 55% over the first 15 minutes of
exercise. They note that the spared glycogen was available late in exercise, which
coincided with a prolonged time to exhaustion.
Obviously, earlier studies seem to indicate that caffeine improves endurance
performance by increasing fat oxidation, which, in turn, allows for muscle glycogen to be
used later on in an event. Unfortunately, however, recent studies have not been able to
replicate these findings. Graham et al looked at leg metabolism after 10 male subjects
performed one hour of exercise on two occasions at 70% VO2 max after ingesting
placebo and caffeine (5). Caffeine ingestion did increase serum free fatty acid and
glycerol concentrations, but there were no differences in respiratory exchange ratio, leg
glucose uptake, muscle glycogenolysis or fatty acid uptake. They concluded that caffeine
does not alter carbohydrate or fat metabolism during exercise.
Laurent et al also studied the effects of caffeine on muscle glycogen utilization.
They had 20 glycogen-loaded subjects consume 6mg/kg of placebo or caffeine 90
minutes prior to cycling for two hours at 65% VO2 max. They found that plasma free
fatty acid concentrations increased and muscle glycogen content decreased similarly in
both groups. They did find almost a doubling of beta-endorphin levels in the caffeine
group however. They concluded that caffeine does not exert a muscle glycogen-sparing
effect, but that it may lower the threshold for beta-endorphin release. They hypothesize
that this may be a potential mechanism for the performance improvements seen in
endurance exercise studies.
Graham wrote two excellent review articles about using caffeine as an ergogenic
aid. When discussing how caffeine improves endurance performance, he concluded that it
is unlikely that increased fat oxidation and glycogen sparing is the prime ergogenic
mechanism (7). He also says that this theory has very little support, and that caffeine may
work by creating a more favorable intracellular ionic environment in muscle, helping to
facilitate force production by the motor units (8). You may recall that caffeine enhances
muscular contractions, likely through increased calcium release from the endoplasmic
reticulum. Another plausible explanation is the decreased perception of effort and altered
mood states that have been noted in other studies. The mechanism of action is assumed to
be multifactorial, and hopefully more research will expand our knowledge base even
further.
What is the Optimal Protocol when using Caffeine?
Caffeine has been established as an effective ergogenic aid during endurance
exercise, but we still need to clear up some important questions. How much caffeine is
enough to affect performance, and when, and in what form, should it be taken?
Researchers have been able to provide some answers, and the findings are pretty
interesting.
Graham and Spriet tried to determine the optimal dose of caffeine by having eight
subjects avoid caffeine for 48 hours, and then ingest placebo or caffeine at doses of 3, 6
or 9mg/kg (9). Afterward, the subjects ran at 85% VO2 max until voluntary exhaustion.
Endurance was enhanced with 3 and 6mg/kg, but not with 9mg/kg. Interestingly, the
highest dose had the greatest effect on epinephrine, yet the least effect on performance.
The authors concluded that the results didn’t support the idea that caffeine exerts its
effect via catecholamines. Pasman et al also addressed this dosage issue (10). They had
nine well-trained cyclists take 0, 5, 9 or 13mg/kg caffeine one hour prior to exercise to
exhaustion at 80Wmax. All caffeine doses improved performance in comparison to
placebo and there were no differences between the three caffeine doses (47 minutes for
placebo and 58 minutes, 59 minutes and 58 minutes for 5, 9 and 13mg/kg respectively).
This study is often referred to when addressing the optimal dose of caffeine, which is
often set at approximately 6mg/kg. For a 70 kg individual, this would be about 420mgs of
caffeine or the equivalent of three to four strong cups of coffee. Certainly, as the caffeine
dose increases, there’s more potential for neuromuscular and gastrointestinal side effects
(jitters and nausea to name a few), though this is very individualized.
Other researchers have tried to determine when caffeine should be taken in order
to enhance performance. This issue resurfaced because many studies have used a bolus
dose one hour prior to exercise, but is this truly the best way to consume caffeine? And
what about the sports nutrition products on the market that contain caffeine that are
designed to be used during events? Conway and his colleagues evaluated the effect of a
divided dose of caffeine on endurance cycling performance (11). Nine cyclists and
triathletes cycled for 90 minutes at 68% VO2 max, followed by a self-paced time trial
(equivalent to 80% VO2 max for 30 minutes). Three different interventions were used:
placebo 60 minutes before and 45 minutes into exercise, caffeine (6mg/kg) 60 minutes
before and placebo 45 minutes into exercise and a divided protocol with caffeine
(3mg/kg) 60 minutes before and again 45 minutes into exercise. The performance was not
different between the two caffeine trials, but interestingly, urinary concentration was
lower post-exercise in the divided dose trial. This had real world application when
caffeine was on the IOC prohibited list because urinary concentration (12ug/ml) was used
as the benchmark for a positive doping test. As mentioned earlier, caffeine is no longer
on the IOC banned list.
Graham looked at one last variable that might alter the effect caffeine has on
endurance performance. Does the form in which caffeine is delivered make a difference?
Nine healthy adults ingested one of five different trials: caffeine or placebo (in water) or
coffee (decaffeinated, decaffeinated with caffeine added or regular coffee) (12). The
caffeine dose was 4.45mg/kg in all caffeine trials. After resting, subjects ran at 85% VO2
max until voluntary exhaustion (about 32 minutes in the placebo and decaffeinated trials).
The main finding here was that endurance only improved in the caffeine capsule trial,
with no differences among the other four trials. The authors speculated that there must be
some component of coffee that lessens the effect of the caffeine.
So What is the Take Home Message?
It seems like the more we know about caffeine, the more we still need to learn. As
with all research, there’s plenty of conflicting evidence, but I think we can make some
strong assertions at this point…
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Caffeine improves performance in endurance exercise, likely through a variety of
systemic effects on the entire body
A variety of caffeine doses have been found to be ergogenic, but in order to
minimize side effects and maximize performance, 6mg/kg seems to be the gold
standard dose
Ingesting a bolus dose of caffeine one hour prior to an event works as well as
divided doses during an event, though the bolus dose may be easier and more
practical in real world settings
Caffeine tablets may be more effective than other sources of caffeine (coffee,
soda, herbs) because of confounding factors and ingredients contained within
these products
Caffeine affects everyone differently, so as always, experiment with it during
training to see how you respond
Brian Zehetner MS,RD,CSSD,CSCS is a sports nutritionist and certified strength and
conditioning specialist living in Woodbury, Minnesota. He owns a sports nutrition
consulting company called Fueling Performance, LLC and can be reached at
bz@fuelingperformance.com or you can visit him online at
www.fuelingperformance.com.
Works Cited
Graham TE, Rush JW, Van Soeren MH. Caffeine and exercise: metabolism and performance. Canadian Journal of
Applied Physiology. 1994 June;19(2):111-38.
Costill DL, Dalsky GP, Fink WJ. Effects of caffeine ingestion on metabolism and exercise performance. Medicine and
Science in Sports. 1978 Fall;10(3):155-8.
Graham TE, Spriet LL. Performance and metabolic responses to a high caffeine dose during prolonged exercise.
Journal of Applied Physiology. 1991 December;71(6):2292-8.
Spriet LL, MacLean DA, Dyck DJ, Hultman E, Cederblad G, Graham TE. Caffeine ingestion and muscle metabolism
during prolonged exercise in humans. American Journal of Physiology. 1992 June;262(6 Pt 1):E891-8.
Graham TE, Helge JW, MacLean DA, Kiens B, Richter EA. Caffeine ingestion does not alter carbohydrate or fat
metabolism in human skeletal muscle during exercise. Journal of Physiology. 2000 December;529 (Pt 3):837-47.
Laurent D, Schneider KE, Prusaczyk WK, Franklin C, Vogel SM, Krssak M, Petersen KF, Goforth HW, Shulman GI.
Effects of caffeine on muscle glycogen utilization and the neuroendocrine axis during exercise. The Journal of Clinical
Endocrinology & Metabolism. 2000 June;85(6):2170-5.
Graham TE. Caffeine, coffee and ephedrine: impact on exercise performance and metabolism. Canadian Journal of
Applied Physiology. 2001;26 Supplement:S103-19.
Graham TE. Caffeine and exercise: metabolism, endurance and performance. Sports Medicine. 2001;31(11):785-807.
Graham TE, Spriet LL. Metabolic, catecholamine, and exercise performance responses to various doses of caffeine.
Journal of Applied Physiology. 1995 March;78(3):867-74.
Pasman WJ, Van Baak MA, Jeukendrup AE, De Haan A. The effect of different dosages of caffeine on endurance
performance time. International Journal of Sports Medicine. 1995 May;16(4):225-30.
Conway KJ, Orr R, Stannard SR. Effect of a divided caffeine dose on endurance cycling performance, postexercise
urinary caffeine concentration, and plasma paraxanthine. Journal of Applied Physiology. 2003 April;94(4):1557-62.
Graham TE, Hibbert E, Sathasivam P. Metabolic and exercise endurance effects of coffee and caffeine ingestion.
Journal of Applied Physiology. 1998 September;85(3):883-9.