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Athletes are among the groups of people who are interested in the effects of caffeine on endurance and exercise capacity. Although many studies have investigated the effect of caffeine ingestion on exercise, not all are suited to draw conclusions regarding caffeine and sports performance. Characteristics of studies that can better explore the issues of athletes include the use of well-trained subjects, conditions that reflect actual practices in sport, and exercise protocols that simulate real-life events. There is a scarcity of field-based studies and investigations involving elite performers. Researchers are encouraged to use statistical analyses that consider the magnitude of changes, and to establish whether these are meaningful to the outcome of sport. The available literature that follows such guidelines suggests that performance benefits can be seen with moderate amounts (~3 body mass) of caffeine. Furthermore, these benefits are likely to occur across a range of sports, including endurance events, stop-and-go events (e.g., team and racquet sports), and sports involving sustained high-intensity activity lasting from 1-60 min (e.g., swimming, rowing, and middle and distance running races). The direct effects on single events involving strength and power, such as lifts, throws, and sprints, are unclear. Further studies are needed to better elucidate the range of protocols (timing and amount of doses) that produce benefits and the range of sports to which these may apply. Individual responses, the politics of sport, and the effects of caffeine on other goals, such as sleep, hydration, and refuelling, also need to be considered.
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Caffeine and sports performance
Louise M. Burke
Abstract: Athletes are among the groups of people who are interested in the effects of caffeine on endurance and exercise
capacity. Although many studies have investigated the effect of caffeine ingestion on exercise, not all are suited to draw
conclusions regarding caffeine and sports performance. Characteristics of studies that can better explore the issues of ath-
letes include the use of well-trained subjects, conditions that reflect actual practices in sport, and exercise protocols that
simulate real-life events. There is a scarcity of field-based studies and investigations involving elite performers. Research-
ers are encouraged to use statistical analyses that consider the magnitude of changes, and to establish whether these are
meaningful to the outcome of sport. The available literature that follows such guidelines suggests that performance benefits
can be seen with moderate amounts (~3 mgkg–1 body mass) of caffeine. Furthermore, these benefits are likely to occur
across a range of sports, including endurance events, stop-and-go events (e.g., team and racquet sports), and sports involv-
ing sustained high-intensity activity lasting from 1–60 min (e.g., swimming, rowing, and middle and distance running
races). The direct effects on single events involving strength and power, such as lifts, throws, and sprints, are unclear. Fur-
ther studies are needed to better elucidate the range of protocols (timing and amount of doses) that produce benefits and
the range of sports to which these may apply. Individual responses, the politics of sport, and the effects of caffeine on
other goals, such as sleep, hydration, and refuelling, also need to be considered.
Key words: ergogenic aid, sports performance, doping.
´:Les athle
`tes font partie des gens concerne
´s par les effets de la cafe
´ine sur l’endurance et la capacite
ˆme si de nombreuses e
´tudes ont porte
´sur les effets de la consommation de la cafe
´ine sur l’exercice physique, elles ne
permettent pas toutes de tirer des conclusions au sujet des effets de la cafe
´ine sur la performance sportive. Pour analyser
de tels effets, il faut des e
´tudes incluant des sujets bien entraı
´s, des conditions refle
´tant les pratiques sportives en cours
et des protocoles expe
´rimentaux simulant des conditions re
´elles. Il y a tre
`s peu d’e
´tudes re
´es sur le terrain qui incluent
des athle
`tes d’e
´lite. On invite les chercheurs a
`utiliser des outils statistiques mesurant l’importance des variations notam-
ment sur le plan de la pertinence dans la pratique sportive. Les e
´tudes scientifiques qui prennent en compte ces directives
rapportent qu’une quantite
´e de cafe
´(~3 mgkg–1 de masse corporelle) suscite des gains sur le plan de la perfor-
mance. De plus, ces gains devraient se manifester dans un large spectre d’activite
´s sportives dont les activite
´s d’endurance,
les activite
´s constitue
´es d’arre
ˆts et de de
´parts tels les sports d’e
´quipe et de raquette et les activite
´s demandant une forte in-
´soutenue de 1 min a
`60 min comme la natation, l’aviron, la course de demi-fond et de fond. Les effets directs de la
consommation de cafe
´ine dans les activite
´s de force et de puissance tels les levers, les lancers et les sprints ne sont pas
bien e
´tablis. Il faut faire d’autres e
´tudes pour bien de
´terminer les varie
´s de protocoles admissibles (moment de l’anne
´e) qui suscitent des gains et qui identifient les sports pouvant en be
´ficier. Il faut aussi faire d’autres
´tudes sur les re
´ponses individuelles, les politiques du sport et sur les effets de la cafe
´ine sur d’autres facteurs tels le som-
meil, l’hydratation et la recharge d’e
´s:facteur ergoge
`ne, performance sportive, dopage.
[Traduit par la Re
Caffeine is a drug that enjoys social acceptance and wide-
spread use around the world, with about 90% of adults con-
suming it in their everyday eating patterns. The effects of
caffeine in reducing fatigue and increasing wakefulness and
alertness have been recognised for many centuries. These
properties have been targeted by shiftworkers, long-haul
truck drivers, members of the military forces, athletes, and
other populations who need to fight fatigue or prolong their
capacity to undertake their occupational activities. Indeed,
the availability, in many countries, of nonprescription medi-
cations, energy drinks, confectionary and sports foods, and
(or) supplements that contain caffeine or guarana (Table 1)
has increased the opportunities for people to specifically
consume caffeine as an ergogenic (work-enhancing) aid.
The past 30 years has seen the publication of a substantial
Received 26 July 2008. Accepted 14 October 2008. Published on
the NRC Research Press Web site at on
6 December 2008.
L.M. Burke. Department of Sports Nutrition, Australian
Institute of Sport, P.O. Box 176, Belconnen, ACT, Canberra
2616, Australia (e-mail:
Appl. Physiol. Nutr. Metab. 33: 1319–1334 (2008) doi:10.1139/H08-130 #2008 NRC Canada
number of studies of caffeine supplementation and exercise
or physical activity. Table 2 provides a summary of our cur-
rent knowledge about the effects of caffeine on exercise ca-
pacity or performance from this robust literature. It is
beyond the scope of this paper to examine the mechanisms
by which caffeine exerts its ergogenic effects related to ex-
ercise on the body; readers are referred to several extensive
reviews for this information (Graham 2001a, 2001b, 2008;
Jones 2008; Keisler and Armsey 2006; Tarnopolsky 2008).
Instead, the aim of this paper is to discuss the available in-
formation on caffeine and exercise from the perspective of
sports performance. It should be noted that the views ex-
pressed in this paper only apply to adult athletes who
already consume caffeine within their normal dietary practi-
ces. This author believes it is inappropriate and unnecessary
for children and young adults to consume caffeine as an er-
gogenic aid, and notes that younger populations have the po-
tential for greater performance enhancement through
maturation and experience in their sport. Caffeine use in all
populations should be seen against the background of its ef-
fects on human health, where it has been suggested that, in
healthy adult populations, moderate daily caffeine intakes of
up to 400 mgd–1 or ~6 mgkg–1 are not associated with ad-
verse effects, whereas children aged 12 or under should
Table 1. Caffeine content of common foods, drinks, and nonprescription preparations.
Food or drink Serving Caffeine, mg*
Instant coffee 250 mL (8 oz) cup 60.(12–169){
Brewed coffee 250 mL (8 oz) cup 80.(40–110){
Short black coffee or espresso 1 standard serving 107.(25–214){
Starbucks Breakfast Blend brewed coffee (Venti size) 600 mL (20 oz) 415.(300–564)§
Iced coffee (commercial brands) 500 mL bottle (16 oz) 30.–200
Frappuccino 375 mL (12 oz) cup 90.
Tea 250 mL (8 oz) cup 27.(9–51){
Iced tea 600 mL (20 oz) bottle 20.–40
Hot chocolate 250 mL (8 oz) cup 5.–10
Chocolate milk 60 g 5.–15
Dark chocolate 60 g 10.–50
Viking chocolate bar 60 g 58.
Coca-Cola 375 mL (12 oz) can 49.
Pepsi cola 1375 mL (12 oz) can 40.
Jolt soft drink 1375 mL (12 oz) can 75.
Red Bull energy drink 250 mL (8 oz) can 80.
Red Eye Power energy drink 250 mL (8 oz) can 50.
V Energy drink 250 mL (8 oz) can 50.
Smart Drink - Brain fuel 250 mL (8 oz) can 80.
Lift Plus energy drink 250 mL (8 oz) can 36.
Lipovitan energy drink 250 mL (8 oz) can 50.
Black Stallion energy drink 250 mL (8 oz) can 80.
AMP Energy tallboy 500 mL (16 oz) can 143.
Spike Shotgun energy drink 500 mL (16 oz) can 350.
Fixx energy drink 600 mL (20 oz) can 500.
Ammo energy shot 30 g (1 oz) 170.
Jolt endurance shot 60 g (2 oz) 150.
PowerBar caffeinated sports gel 40 g sachet 25.
PowerBar double caffeinated sports gel 40 g sachet 50.
GU caffeinated sport gel 32 g sachet 20.
Carboshotz caffeinated sports gel 50 g sachet 80.
PB Speed sports gel 35 g sachet 40.
PowerBar Acticaf Performance bar 65 g bar 50.
Jolt caffeinated gum 1 stick 33.
No-Doz (Australia) 1 tablet 100.
No-Doz (U.S.) 1 tablet 200.
Extra Etrength Excedrin 1 tablet 65.
*These values were gathered from a variety of sources, including manufacturers’ information and nutrition databases (Centre
for Science in the Public Interest (available at, and USDA National Nutrient Database
(available at Note that commercial brands may vary slightly from country to
{The caffeine content of tea and coffee varies widely, depending on the brand, the way the beverage is made, and the size of the
mug or cup.
{Commercial samples bought from a variety of outlets (Desbrow et al. 2007).
§Commercial samples bought from the same Starbucks outlet (McCusker et al. 2003).
1320 Appl. Physiol. Nutr. Metab. Vol. 33, 2008
#2008 NRC Canada
limit their caffeine intake to <2.5 mgkg–1d–1 because of
their increased risk of behavioural side effects (Nawrot et
al. 2003).
Special issues related to study design for
examining caffeine and sports performance
Research design reflects a number of scientific and practi-
cal concerns, including the primary question (hypothesis) of
interest, level of funding, the availability and limitations of
equipment and subjects, interest in examining the mecha-
nisms underpinning outcomes, approval from ethics panels,
and the requirements or expectations of participants in the
peer-review process. Given the range of potential uses for
any beneficial effects of caffeine on physical and occupa-
tional activities, and the diverse interests of scientists who
have undertaken studies of caffeine and exercise, we might
expect that a variety of research protocols have been under-
taken. While many studies may have been able to address
issues related to caffeine and exercise per se, not all were
well suited to address special issues of sports performance.
Table 3 summarizes some of the characteristics of the
methodologies used in many studies of caffeine supplemen-
tation and exercise, and contrasts these with the features of
real-life sport.
One of the key tenets of research is that the results really
only apply to the population and the situation that was in-
vestigated. Therefore, Table 3 provides a list of the charac-
teristics that should be included in studies specifically
designed to investigate the effect of caffeine on sports per-
formance. It is likely that there is a spectrum of athletes
who are interested in the outcomes of such research. The re-
wards for achieving success in elite-level sports are highly
visible and offer a clear incentive to search for strategies
that can enhance performance by even a small margin.
Theoretically, the potential for detecting small but worth-
while changes in performance should be greater among elite
athletes. After all, elite athletes are usually highly reliable at
performing the tasks for which they have trained; a small
coefficient of variation in performance increases the preci-
sion of the separation of the true effects of an intervention
(the signal) from everyday differences in performance (the
Ironically, few studies on caffeine and elite athletes are
available. This is understandable because, by definition,
they are few and special. It is usually difficult to achieve a
large sample size of elite athletes for statistical rigour or to
impose the conditions or invasive techniques of research on
their training and competition schedules. Therefore, most
studies of caffeine and sports performance have been under-
taken on athletes at recreational to highly trained but sub-
elite levels (Tables 4–7). It is unclear whether the results of
Table 2. A summary of our current understanding of the effect of caffeine supplementation on exercise capacity or performance.
Issue Supporting evidence
There is sound evidence that caffeine enhances endurance and provides a small but
worthwhile enhancement of performance over a range of exercise protocols, with
the traditional protocol involving a caffeine dose of ~6 mgkg–1 body mass taken
1 h pre-exercise.
Jones (2008); Keisler and Armsey (2006); Doh-
erty and Smith (2004); Graham (2001a, 2001b)
Recent studies show that beneficial effects from caffeine occur at very modest levels
of intake (1–3 mgkg–1 body mass, or 70–150 mg caffeine).
Bridge and Jones (2006); Cox et al. (2002);
Kovacs et al. (1998); Graham and Spriet (1995)
Several studies suggest there is no dose–response relationship between caffeine
intake and benefits to endurance exercise or, if a dose–response exists, there is a
plateau at ~3 mgkg–1.
Anderson et al. (2000); Bruce et al. (2000); Cox
et al. (2002); Kovacs et al. (1998); Pasman et al.
(1995); Graham and Spriet (1995)
A variety of protocols of caffeine intake, including doses before or during exercise,
or after the onset of fatigue, may be beneficial for exercise capacity.
Cox et al. (2002); Kovacs et al. (1998)
Some tissues become tolerant to repeated caffeine use, while others do not. Since the
mechanisms by which caffeine exerts effects on performance are not fully known,
it is unclear whether an athlete should withdraw from caffeine prior to competition.
Some studies show that there is no difference in the performance response between
nonusers and users of caffeine. Withdrawal can be achieved by 24–48 h of
cessation of caffeine use. However, athletes should be aware of the side effects of
withdrawal, such as headaches, and the greater potential for negative side effects
from subsequent caffeine exposure.
Graham (2001b)
The effects of caffeine can be long lasting. Although there is some evidence that the
benefits do not persist up to 6 h, people who ingest caffeine to enhance a morning
exercise task may still receive benefits during a session undertaken later in the day.
Bell and McLellan (2002, 2003)
Coffee may not be a good source of caffeine for exercise enhancement; it is difficult
to know the dose of caffeine in any serving of coffee. Some studies have found
that while caffeine alone was ergogenic for a given exercise task, caffeine
consumed in a caffeine medium did not enhance performance of the same protocol.
Coffee may contain other ingredients that counteract the benefits of caffeine.
Nevertheless it appears that caffeine is ergogenic when coffee is consumed with a
prerace meal.
Graham et al. (1998); Graham (2001a, 2001b)
There is individual variability in the changes in exercise capacity in response to
caffeine. Some people are nonresponders to caffeine.
Graham and Spriet (1995)
Higher doses of caffeine (>6–9 mgkg–1) may be associated with side effects, such as
jitters, increased heart rate, and performance impairment.
Graham and Spriet (1995)
Burke 1321
#2008 NRC Canada
current research apply to the true elite, since top competitors
may have unusual characteristics, as a result of genetics or
conditioning, that have made them the best. However, we
can be sure that the population base to which the results of
currently available studies of caffeine and exercise and (or)
sport best apply is far larger than the elite athlete popula-
tion. It should also be remembered that athletes at lower lev-
els of competition can also be highly motivated, even if the
rewards are simply the satisfaction of achieving personal
bests. As such, they will be highly interested in utilizing the
results of caffeine studies. Although it would be good to see
more studies of elite athletes, the practicalities that prevent
this will mean that top class athletes will need to extrapolate
the information on protocols for caffeine in sport from stud-
ies of well-trained athletes, and to test what works for their
individual situation.
Sports scientists who work with athletes are understand-
ably interested in investigations that have been carried out
in a field setting or in a situation of sport (Berglund and
Hemmingsson 1982; Cohen et al. 1996; Van Nieuwenhoven
et al. 2005). The advantages of such studies relate to the val-
idity of performance measures, since they can include fea-
tures such as real airflow and ground resistance, real-life
pacing strategies (which are often stochastic), changes in
the environment and course over the event, and the effect
of competition and other extrinsic motivating factors. The
negatives of field and real-life settings typically include a
reduction in the control that is possible over the environ-
ment and the athlete. This is likely to reduce the precision
of the results and, therefore, the likelihood of detecting
small changes that could be important.
Therefore, it is important to recognise that our interest in
caffeine exists because of the laboratory-based studies in
which tight control has allowed the effects on metabolism
and exercise capacity or performance to be detected. As
well as selecting an appropriate subject pool, there are fea-
tures that can be built into laboratory (or field) studies to en-
hance the reliability and validity of the results in relation to
sporting activities. Table 3 lists many such factors, including
the choice of performance tasks that are related to sport, the
control or standardization of training and diet leading into
performance trials, and the choice of conditions that mimic
what happens in the world of sport. For example, some re-
cent studies of caffeine and endurance sports that have re-
quired subjects to be well fuelled from the days and the
meal leading into a performance trial, and have provided
carbohydrate intake during prolonged events are helpful
(Cox et al. 2002). Similarly, studies examining the inter-
action of caffeine with other proven ergogenic aids, such as
creatine (Doherty and Smith 2004) and bicarbonate
(Pruscino et al. 2008), are important, since this is a likely
scenario in real life.
The analysis and interpretation of the results of studies
need to be undertaken with sympathy for effect sizes that
would be worthwhile to an athlete. In many sports, the mar-
gins between winning and losing can be measured to several
decimal points. An emerging area in sports science is the
use of magnitude-based statistics, which look at the range
of the likely true effect of an intervention in comparison to
the differences in performance that might change the out-
come of an event (Batterham and Hopkins 2006). In fact,
Table 3. The characteristics of traditional laboratory-based research vs. research focussed on elite sports performance.
Characteristics of traditional studies Characteristics of elite and serious sport Comments on the ideal characteristics of studies on sports performance
Subjects are often drawn from available populations,
such as college students or recreationally and
moderately trained subjects.
Competitors are highly trained in their sport and event. Characteristics
include reliability in repeating a given performance task, and
specific adaptations achieved though natural selection of sport and
the conditioning effects of training.
Subjects should reflect the population to which the results of the study
are intended to apply; subjects should be familiar with and reliable in
undertaking the performance protocol; and studies that involve elite
or highly trained athletes are underrepresented and should be
Exercise protocols typically measure endurance or
exercise capacity (the ability to sustain a given
exercise task for as long as possible). The task is
terminated when the subject is fatigued and unable to
continue at the prescribed output.
Sports performance typically includes completing a task in the fastest
possible time (pace judgement is important), executing skills and
making complex decisions while undertaking exercise, and
executing a single task as well as possible. Training situations may
better represent the execution of an exercise task to fatigue.
Protocols should involve a close-looped task (i.e., completing a task in
the fastest time possible), which involves pacing rather than simply
exercising to fatigue; protocols should simulate, as much as possible,
a real-life event; and field studies are underrepresented and should be
Protocols are often undertaken with baseline metabolic
conditions (subjects fast overnight and consume only
water during exercise) and without the confounding
effects of other nutritional strategies.
Athletes undertake other nutrition strategies that provide additional
support for performance, including eating a carbohydrate-rich pre-
event meal consuming carbohydrates during prolonged events, and
using other scientifically supported ergogenic aids (e.g., bicarbonate,
Protocols should allow subjects to follow nutrition strategies that
optimize performance and reflect the real-life practices of athletes;
and studies should investigate the interaction between caffeine intake
and other nutrition strategies or supplements, and their combined
effect on performance.
Differences (which must reach a level of >5%
probability to be considered significant) in
performance between the control treatment and the
active treatments(s) are assessed using probability
The margins between winning and losing, or between the ‘‘podium’
athletes (first-, second-, and third-place winners) and the rest of the
field, can often be measured in hundredths of seconds and meters.
Differences in performance should be assessed using magnitude-based
statistics: the likely range of the true difference in performance
should be compared with the coefficient of variation of performance
for individuals undertaking that protocol.
Protocols are conducted with consideration to the
concerns of the ethics committee overseeing the
Sports are conducted within the regulations of their governing body,
and many athletes compete within an anti-doping code that may not
permit the use of otherwise legal products or strategies.
Projects that are focussed on high-level sports should be conducted
within the logistical and anti-doping rules that govern athletes in that
1322 Appl. Physiol. Nutr. Metab. Vol. 33, 2008
#2008 NRC Canada
Table 4. Crossover-designed studies of caffeine supplementation related to an endurance sport (>60 min).
Publication Subjects Caffeine intake Sports performance
performance Comments
Jenkins et al. (2008) Trained cyclists
(13 males)
(60 min pre-exercise)
15 min cycling (60%
) + 15 min TT
Yes for 2 and
doses; no for
1mgkg–1 dose
Work done during the 15 min TT was
increased by 4% (1–6.8) with 2 mgkg–1
of caffeine and by 3% (–0.4%–6.8%)
with 3 mgkg–1; improvement varied in
magnitude between individual cyclists
Cureton et al.
Well-trained cyclists
(16 males)
Total, 5.3 mgkg–1; 1.2 mgkg–1
pre-exercise + 0.6 mgkg–1 every
15 min during exercise
120 min cycling (60%
and 75% VO2max
15 min TT; CHO-fed
during cycling
Yes Higher exercise intensity in 15 min TT
with caffeine and CHO (90±11%
) vs. CHO alone (79±14 VO2max
Conway et al.
Trained cyclists and
triathletes (9 males)
6mgkg–1 60 min pre-exercise;
3mgkg–1 pre-exercise; and
3mgkg–1 at 45 min during
90 min cycling at 68%
VO2max + TT (~30 min)
Perhaps Trend to better performance in TT with
caffeine trials (~24.2 and 23.4 min) vs.
placebo (28.3 min) (p= 0.08); urinary
caffeine concentrations lower with split
Hunter et al. (2002) Highly trained
cyclists (8 males)
6mgkg–1 60 min before exercise +
0.33 mgkg–1 every 15 min
100 km cycling TT,
including 5 1 km and
44 km high-intensity
efforts; CHO-fed during
No No difference between trials with respect to
total 100 km time or time to complete
high-intensity efforts; no difference
between trials in EMG characteristics,
although differences within trial
attributable to workload
Cox et al. (2002) Well-trained cyclists
and triathletes
(12 males)
6mgkg–1 60 min pre-exercise; 6
1 mg every 20 min during
exercise; 10 mLkg–1 Coca-Cola
in last 50 min (~1–1.5 mgkg–1
2 h cycling at 70%
VO2max +7kJkg–1 TT
(~30 min); CHO-fed
during cycling
Yes at all doses Compared with placebo, caffeine in large
dose (6 mgkg–1) provided 3%
performance benefit in TT, regardless of
timing of intake; commercial cola drink
consumed late in exercise (~1 mgkg–1
caffeine) produced effects of equal
magnitude; urinary caffeine levels
~4–5 mgmL–1 for large dose of caffeine
and <1 mgmL–1 for cola drink
Cox et al. (2002) Well-trained cyclists
and triathletes
(8 males)
Sports drink replaced during last
70 min with 15 mLkg–1 of a cola
drink (caffeine dose ~1.5 mgkg–1):
6% CHO; 11% CHO; 6% CHO +
130 mgmL–1 caffeine; or 11%
CHO + 130 mgmL–1 caffeine*
2 h cycling at 70%
VO2max +7kJkg–1 TT
(~30 min); CHO-fed
during cycling
Yes Commercial cola drink consumed late in
exercise produced 3% performance
benefit in TT compared with cola-
flavoured placebo drink. Benefits
attributable to caffeine content (~2%) and
increased CHO intake (~1%)
Jacobson et al.
Trained cyclists
(8 males)
6mgkg–1 (60 min pre-exercise) 2 h cycling at 70%
VO2max +7kJkg–1 TT
(~30 min); CHO-fed
during cycling
No TT performance similar in caffeine + CHO
trial (29.12 min) and CHO trial
(30.12 min), with both trials better than
placebo trial
Ivy et al. (1979) Trained cyclists
(9 males + females)
Total dose, 500 mg; 250 mg at
60 min pre-exercise + 7 doses
during exercise
2 h isokinetic cycling at
80 rmin–1
Yes 7% increase in total work, compared with
placebo trial; RPE same, despite
increased work
Burke 1323
#2008 NRC Canada
Table 4 (concluded).
Publication Subjects Caffeine intake Sports performance
performance Comments
Kovacs et al. (1998) Well-trained cyclists
(15 males)
2.1 mgkg–1, 3.2 mgkg–1, and
4.5 mgkg–1 doses; 75 min
pre-exercise and at 20 and 40 min
during TT
Cycling TT of about
~1 h; CHO-fed during
Yes at all doses Addition of caffeine to CHO–electrolyte
drinks improved 60 min TT performance;
improvement with 3.2 and 4.5 mgkg–1
caffeine doses equal to and greater than
improvement with 2.1 mgkg–1; urinary
caffeine levels related to total dose, but
all below 12 mgmL–1
Cross-country Skiing
Berglund and
Well-trained cross-
country skiers
(14 males)
6mgkg–1 (prerace) 21 km cross-country ski
race (field study) at low
and high altitudes
Perhaps at low
altitude; yes at
high altitude
Race times were normalized to account for
differences in weather (individual times
expressed as % of mean race time); at
low altitudes, at half way, the race time
with caffeine was decreased by 0.9% of
the mean time (~33 s), compared with
placebo (p< 0.05); at full distance,
decrease was 1.7% of the mean time
(~59 s) (p< 0.1); at high altitudes, the
race time was significantly faster with
caffeine than with placebo (p< 0.001)
both after 1 lap (2.2% or ~101 s) and 2
laps (3.2% or ~152 s)
Distance running
Cohen et al. (1996) Trained runners
(5 males + 2
5mgkg–1,9mgkg–1 (prerace) 21 km half-marathon
(field study)
No No effects on RPE or performance at either
dose, compared with placebo
Van Nieuwenhoven
et al. (2005)
Trained to well-
trained runners
(90 males + 8
~1.3 mgkg–1 in 7% CHO sport
drink vs. CHO sport drink alone +
water (pre-exercise and at 4.5, 9,
and 13.5 km during race)
18 km road running race
(field study); CHO-fed
during some trials
No No differences in performance of whole
group between caffeinated sport drink
(78:03±8:42 min:s), sport drink
(78:23±8:47 min:s), or water (78:03±8:30
min:s), or for 10 fastest runners (63:41,
63:54, and 63:50 min:s for caffeine sport
drink, sport drink, and water,
Note: CHO, carbohydrate; EMG, electromyographical; RPE, rate of perceived exertion; TT, time trials; VO2 max, maximal oxygen consumption.
*Caffeine content equivalent to Coca-Cola.
1324 Appl. Physiol. Nutr. Metab. Vol. 33, 2008
#2008 NRC Canada
Table 5. Crossover-designed studies of caffeine supplementation and performance of sustained high-intensity sports (1–60 min).
Publication Subjects Caffeine intake Sports performance
performance Comments
Middle distance and distance running
Bridge and Jones
Distance runners
(8 males)
3mgkg–1 (60 min pre-exercise) 8 km race on track Yes Relative to the mean time of the control and
placebo trials, caffeine supplementation
resulted in a 23.8 s or 1.2% improvement in
run time (p< 0.05), with individual
improvements ranging from 10 to 61 s; heart
rate was significantly higher in caffeine trial,
with trend toward lower RPE, despite faster
running speed
Wiles et al. (1992) Well-trained runners
(18 males)
3 g of coffee (150–200 mg of
caffeine) 60 min pre-exercise
1500 m race on treadmill Yes Mean time improved by ~4.2 s (p< 0.05) with
caffeine, compared with placebo
Wiles et al. (1992) Well-trained runners
(10 males)
3 g of coffee (150–200 mg
caffeine) 60 min pre-exercise
1500 m race: 1100 m at
constant speed and 1 min
final burst at self-selected
Yes Caffeine enhanced speed of 1 min final burst by
~0.6 kmh–1, equivalent to 10 m (p< 0.05)
Bruce et al. (2000) Well-trained rowers
(8 males)
6mgkg–1 or 9 gkg–1 60 min
2000 m ergometer row Yes for both
Caffeine enhanced performance by a mean of
1.3% and 1% for 6 mgkg–1 and 9 gkg–1
doses, respectively, compared with placebo
(p< 0.05); some participants had urinary
caffeine concentrations >12 ngmL–1 with
higher caffeine dose, but participants were
unable to identify caffeine trials, suggesting
that effect is subtle
Anderson et al.
Well-trained rowers
(8 females)
6mgkg–1 or 9 gkg–1 60 min
2000 m ergometer row Yes for both
Caffeine enhanced performance by a mean of
0.7% and 1.3% for 6 mgkg–1 and 9 gkg–1
doses, respectively, compared with placebo
(p< 0.05); performance improvement achieve
primarily by enhancing the first 500 m
Burke et al.
(unpublished ob-
Elite and highly
trained swimmers
(15 males +
2mgkg–1 60 min prerace 100 m race (best stroke) No, but
lower RPE
No difference in reaction time, 50 m split, or
100 m race time between trials, but ratings of
perceived exertion was lower in the caffeine
trial (16.6 vs. 17.1; p= 0.01); self-reports of
sleeping patterns following the trial found that
caffeine supplementation was associated with
an increase in time taken to fall asleep and a
reduction in quality of sleep
MacIntosh and
Wright (1995)
(11 males +
6mgkg–1 60 min prerace 1500 m freestyle race Yes 23 s improvement in swimming time with
caffeine (p< 0.05); caffeine affected substrate
and electrolyte balance
Burke 1325
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these performance differences are not the hundredths of sec-
onds or millimetres that often separate competitors or a win-
ning shot from a miss in the memorable moments of sport.
Rather, the modelling of athletic performances has shown
that they are related to the coefficient of variation of per-
formers in the event (Hopkins et al. 1999). Readers are di-
rected to the work of Will Hopkins and colleagues, which
describes this new approach (Batterham and Hopkins 2006;
Hopkins et al. 1999) and provides resources with which to
undertake it (
It is sometimes difficult to convince the reviewers of jour-
nals to accept this new approach, and some researchers try
to combine traditional probability-based statistics with a
more athlete-friendly interpretation. For example, Wiles and
colleagues (2006) undertook a laboratory-based study simu-
lating the 1 km cycling time trial in track cycling. They
found that caffeine supplementation enhanced the perform-
ance of trained cyclists by a mean of 2.4 s, or 3.1%, which
achieved statistical significance. However, in highlighting
the relevance of these results, they noted that the 95% con-
fidence limits of this effect (the range of likely true effects
in a similar cycling population) showed a decrease in 1 km
time, ranging from 0.7% to 5.6%. To put this into context,
at the mens 1 km event at the 2004 Summer Olympic
Games in Athens, the difference between the gold and silver
medal performances was 0.0185 s, or 0.3%, while the differ-
ence between first and tenth place was 2.39 s (Wiles et al.
Finally, the issue of the blinding of caffeine supplementa-
tion is important to consider. A double-blinded application
of an intervention, in which neither the subject nor the re-
searcher know which treatment has been received, is consid-
ered a benchmark of study design. However, because
caffeine has effects on various body functions, subjects are
sometimes able to detect whether or not they have received
an active treatment from clues such as changes in heart rate
or arousal. The placebo effect has been well documented in
sport. In fact, studies in which trained subjects were told
that they were receiving caffeine showed a dose-dependent
improvement in cycling time-trial performance (small im-
provement when they thought they were receiving a small
caffeine dose, and larger improvement when they thought
they were receiving a large caffeine dose), even when they
actually received an inert substance on all occasions (Beedie
et al. 2006). Since the perceived benefit of a treatment may
actually allow subjects to perform better, researchers should
consider strategies to minimize or at least recognise the pos-
sibility that the placebo effect occurs in response to the un-
masking of a blinded treatment. Asking subjects to rank the
order of their treatments and their performance results may
uncover whether the placebo effect could be, at least in
part, responsible for performance outcomes.
Studies of caffeine and sports performance
So what does the current scientific literature say about the
effect of caffeine on sports performance? A summary has
been prepared that includes studies that meet as many of
the criteria outlined in Table 3 as possible, but with particu-
lar focus on the use of trained subjects, and an exercise pro-
tocol involving a close-looped outcome rather than time to
Table 5 (concluded).
Publication Subjects Caffeine intake Sports performance
performance Comments
Collomp et al.
Trained swimmers
(14 males +
250 mg (~4 mgkg–1) 60 min
2100 m swimming races,
separated by 20 min
Yes Caffeine enhanced mean swimming velocity in
both 100 m races (p< 0.01), and prevented the
decrease in velocity otherwise seen in the
second swim with the placebo treatment
Track cycling
Wiles et al. (2006) 8 trained cyclists 5 mgkg–1 75 min pre-exercise 1 km cycling TT Yes Performance improved by a mean of 2.4 s or
3.1% (95% CI, 0.7% to 5.6%; p< 0.05),
which also achieved practical significance in
context of real-life 1 km track cycling event
1326 Appl. Physiol. Nutr. Metab. Vol. 33, 2008
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Table 6. Crossover-designed studies of caffeine supplementation and stop-and-go sports (team and racquet sports).
Publication Subjects Caffeine intake Sports performance
performance Comments
Team sports
Stuart et al. (2005) Rugby union players
(9 males)
(70 min pre-exercise)
240 min circuits
(simulated rugby union
protocol), involving
repetitions of:
Study involved probability statistics rather than
testing of null hypothesis. Interpretation
included change in fatigue with caffeine,
compared with placebo. Mean improvements of
0.5%–3% in performance of sprint tasks, with
greater improvement in second half. Suggests
caffeine effect achieved by reduction in fatigue.
Improvement (10%) in ability to pass ball
accurately because of enhancement of arousal
or attention.
20 m sprint speed Possible
30 m sprint speed Very likely
Offensive sprint Likely
Defensive sprint Likely
Drive 1 power Likely
Drive 2 power No, harm
Tackle speed Likely
Passing ability Likely
Schneiker et al. (2006) Team athletes
(10 males)
(60 min pre-exercise)
236 min cycle protocol,
each involving:
Total work during sprints in first half was 8.5%
greater in caffeine trial than placebo, and work
in second half was 7.6% greater in caffeine trial
(p< 0.05 for both). Mean peak power score
achieved during sprints in first and second
halves were 7% and 6.6% greater, respectively,
in caffeine trial than in placebo trial (p< 0.05
for both).
18 4 s sprint with
2 min recovery
Paton et al. (2001) Team athletes
(16 males)
(60 min pre-exercise)
10 20 m sprints on
interval of 10 s
No Negligible difference between caffeine and
placebo trials for time to complete 10 sprints
and decay in performance over 10 sprints.
Racquet sports
Strecker et al. (2007) Collegiate tennis
players (10 males)
(90 min pre-exercise)
Skill test performed pre-
exercise, 30 min, 60 min,
and 90 min during
simulated tennis play
against a ball machine (15
ground strokes in all 4
directions; 60 shots total):
Caffeine trial showed better performance of both
forehand shots across the 90 min of simulated
tennis play. There was no difference in skill in
backhand shots between trials.
Forehand cross-court Yes
Forehand up the line Yes
Backhand cross-court No
Backhand up the line No
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fatigue. There are relatively few investigations that meet
these criteria in the larger literature on caffeine and exercise
(Doherty and Smith 2004); these have been grouped accord-
ing to the characteristics of endurance (Table 4), sustained
high-intensity (Table 5), stop-and-go (Table 6), and strength
and (or) power (Table 7) sports.
The majority of the studies of caffeine and athletic per-
formance concern endurance sports, including running, cy-
cling, and cross-country skiing events. These provide
reasonable but not unanimous support that caffeine use can
be beneficial for these activities. A variety of protocols ap-
pear to be useful, including intake before and during the
event, and investigations using relatively low doses of
caffeine (2–3 mgkg–1) have been more prevalent in these
sports. There is also evidence that caffeine can enhance
performance of sustained high-intensity events (lasting 1–
20 min) in running, cycling, swimming, and rowing. It is
more difficult to find clear support for benefits to the per-
formance of work patterns and skills activities within team
and racquet sports. Whether the effect of caffeine is smaller
or absent in these sports, or whether the current studies are
confounded by problems in the reliability or validity of pro-
tocols, requires further examination. Finally, there is a
dearth of studies involving strength or power, such as true
sprints, lifts, and throws; therefore, there is currently a lack
of information on the effect of caffeine on such events.
Other effects of caffeine related to sports
nutrition goals
The previous section examined the effects of specific sup-
plementation with caffeine on the performance of a single
bout of exercise, with the most immediate application being
the outcome of a competitive event. However, any summary
of the effects of caffeine for an athlete should be widened to
consider issues of training and recovery. It is beyond the
scope of this paper, and indeed the scientific literature, to
consider the effect of caffeine on repeated bouts of exercise
within a single session or from day to day (i.e., the training
scenario). Nevertheless, it is reasonable to speculate that the
habitual social intake of caffeine, or its specific use in rela-
tion to a training session, may have some benefits in
promoting endurance — that is, prolonging the athlete’s ca-
pacity to undertake the physical and mental components of
their workout. Therefore, caffeine use may indirectly en-
hance competition performance by allowing the athlete to
train hard.
There are several other effects of caffeine that may make
an indirect contribution to or may impair sports perform-
ance. First, the effect of caffeine on promoting wakefulness
or interfering with sleep must be considered in the practical
context of sport. In many sports, the outcome of a competi-
tion is decided through a series of races or games spread
over days — for example, heats and semi-finals before the
final event, or the schedule of matches in a tournament. In
studies of exercise in the military context, caffeine has been
shown to combat the effects of sleep deprivation on the per-
formance of mentally and physically challenging tasks.
However, there are no studies that satisfactorily consider
that caffeine use by athletes in competition could potentially
contribute to sleep deprivation after the first event and im-
Table 6 (concluded).
Publication Subjects Caffeine intake Sports performance
performance Comments
Vergauwen et al. (1998) Well-trained tennis
players (13 males)
1 h pre-exercise +
0.75 mgkg–1h–1 over
2 h; separate trials for
caffeine + CHO,
CHO only, and
Tests undertaken pre and
post 2 h match play:
CHO trial resulted in maintenance of stroke
quality and shuttle run speed, whereas placebo
trial resulted in deterioration of these aspects of
performance. Caffeine added to CHO did not
further enhance post-trial performance. Authors
suggest that caffeine dose was too high.
However, it is also possible that effect could
only be expected if protocol had caused fatigue,
and this did not occur because of CHO intake.
Skills test (Leuven
Tennis Performance
Test) measuring stroke
70 m shuttle run (CHO
consumed in some
Ferrauti et al. (1997) Competitive tennis
players (8 males + 8
364 mg for males,
260 mg for females
(~4–4.5 mgkg–1)
4 h singles tennis (with
30 min break after
150 min); tests of skill
and speed undertaken at
end of 4 h:
No effect of caffeine supplementation on tennis-
specific running speed; caffeine trial not
different than placebo trial. No effect on hitting
accuracy or success of games played during 4 h
with male participants. However, female
players had greater success during tennis play
on caffeine than on placebo.
615 min sprint with
30 min rest
Hitting accuracy and
success during games
males, no
1328 Appl. Physiol. Nutr. Metab. Vol. 33, 2008
#2008 NRC Canada
pair the performance of subsequent events. It would be val-
uable if future studies of caffeine and performance of an ex-
ercise task examined whether caffeine doses that are found
to be ergogenic also affect the quality and duration of sleep
during the night following the exercise task. More sophisti-
cated studies are needed to measure the carryover effect of
caffeine-related impairment of sleep on subsequent perform-
ance. This would be an important issue to study because
there is at least anecdotal evidence that some athletes resort
to a cycle of caffeine supplementation followed by use of
sleeping agents during a multiday competition. Until such
studies can be undertaken, it would seem prudent for scien-
tists and athletes to look for the smallest dose of caffeine
that is ergogenic for sports performance.
Another indirect way in which caffeine supplementation
can affect sports performance is through its impact on hy-
dration status during exercise or in the recovery between ex-
ercise bouts. Acute intake of caffeine is known to have a
diuretic effect — that is, to increase urine excretion. Indeed,
common education messages regarding caffeine include ad-
vice to limit caffeine intake in situations in which hydration
is challenged (e.g., air travel) or to consume extra fluid in
combination with the intake of caffeine. There are a few
studies involving exercise and hydration that show that caf-
feine can have a numeric effect on fluid losses. For exam-
ple, during recovery from exercise, the intake of caffeine
from cola beverages has been shown to cause a small but
statistically significant increase in urine production, com-
pared with hydration with caffeine-free fluids (Gonzalez-
Alonso et al. 1992). However, a recent review of caffeine
and hydration status found that there is little scientific evi-
dence that caffeine intake impairs overall fluid status
(Armstrong 2002). That report concluded that the effect of
caffeine on diuresis is overstated and may be minimal in
people who are habitual caffeine users. In fact, many studies
that have examined caffeine supplementation and fluid bal-
ance have found that doses of caffeine that are within the
range proven to be ergogenic do not alter sweat rates, urine
losses, or indices of hydration status during exercise
(Millard-Stafford et al. 2007; Wemple et al. 1997). Chronic
daily intakes of caffeine, or a sudden increase in caffeine in-
take, have also been shown not to impair body fluid balance
(Armstrong et al. 2005; Fiala et al. 2004). Therefore, it
seems that athletes do not need to alter their fluid intake
strategies to accommodate caffeine use or to avoid otherwise
successful caffeine supplementation strategies in hot weather
or other dehydrating environments.
Finally, caffeine is known to have a range of apparently
contradictory effects on carbohydrate metabolism, including
short-term impairment of insulin-mediated glucose disposal
in response to an acute dose at rest, along with an ap-
parently protective effect (at least for coffee consumption)
on the development of type II diabetes (for review, see van
Dam and Hu 2005). One outcome of an effect of caffeine on
glucose disposal would be to impair the synthesis of muscle
glycogen, a key element of recovery after prolonged or
high-intensity exercise. However, Battram and colleagues
(2004) found that the intake of 6 mgkg–1 of caffeine before
and during glycogen-depleting exercise did not affect the
rate of glycogen synthesis during the 5 h of recovery when
adequate amounts of carbohydrate were consumed. There
has been recent attention directed to the results of a study
reporting enhanced muscle glycogen resynthesis following
glycogen-depleting exercise in well-trained subjects. In that
study, the intake of large amounts of caffeine after exercise
(8 mgkg–1) were found to enhance the rates of muscle gly-
cogen synthesis over 4 h of recovery, by 66%, when co-
ingested with carbohydrate (Pedersen et al. 2008). In fact,
the rates of sustained postexercise glycogen synthesis over
this time period were among the highest reported in the lit-
erature. However, the intake of such high doses of caffeine
may cause side effects in some subjects or may interfere
with other aspects of recovery, such as the quality of sleep
(see earlier). As such, they may be impractical for use in
sport. Further studies are needed to examine whether this ef-
fect is seen at lower levels of caffeine intake.
The politics of caffeine in sport
The 1984 Summer Olympic Games in Los Angeles saw
the introduction of an anti-doping program by the Interna-
tional Olympic Committee, involving the testing of a single
urine sample collected after an event for the absence or
presence of items described on a list of prohibited substan-
ces. Caffeine was included on that list, with the definition
of a doping offence being a urinary caffeine exceeding a
cutoff of 15 mgmL–1. This threshold was reduced in 1985
to 12 mgmL–1. The cutoff value was chosen to exclude nor-
Table 7. Studies of caffeine supplementation and performance of power events (throws, lifts, sprints <20 s).
Publication Subjects Caffeine intake Sports performance
performance Comments
Astorino et al.
22 resistance-
trained males
(60 min pre-
1 RM bench press No No changes in strength of lower or
upper body with caffeine
1 RM leg press No
Beck et al.
37 resistance-
trained males;
design (trials
48 h apart)
(60 min pre-
1 RM bench press Yes Caffeine supplement group showed
a 2% (2 kg) increase in upper
body strength (1 RM bench press)
following treatment, but no
change in placebo group; there
were no differences in lower body
strength in either group
1 RM leg extension No
Note: RM, repetition maximum.
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mal or social coffee drinking (Delbeke and Debackere 1984)
and to target the doses of caffeine that were being found to
be ergogenic in the studies of the time. Indeed, with caffeine
supplementation of up to 5–6 mgkg–1, positive urinary caf-
feine levels are unlikely (Conway et al. 2003; Cox et al.
2002; Kovacs et al. 1998; Pasman et al. 1995); a substantial
risk of urinary caffeine values greater than 12 mgmL–1 does
not occur until intakes are greater than 9 mgkg–1 (Pasman et
al. 1995). It is unclear whether this ban was primarily re-
lated to safety concerns over intakes of very large doses of
caffeine or the ethics of achieving performance advantages
through caffeine use. In any case, there were relatively few
cases of positive doping outcomes for caffeine use among
elite athletes over the subsequent decade.
In the new millennium, the landscape of caffeine in sport
has changed markedly. First, there is greater awareness of
the frailty of urinary caffeine concentrations as a marker of
caffeine use. Urinary concentration reflects the small amount
(~1%) of plasma caffeine that escapes metabolism and is ex-
creted unchanged. Metabolic clearance of caffeine varies
widely among athletes and among different occasions of use
by the same athlete (Birkett and Miners 1991). Urinary caf-
feine levels are determined by a variety of factors, including
the size of caffeine dose, the metabolic clearance of caf-
feine, and the timing of the urine sample in relation to the
caffeine dose. Since there is huge variation in urinary caf-
feine content for the same caffeine dose, and neither the
standardization of the time between caffeine intake and
urine collection nor the prevention of opportunities to uri-
nate during or after an event, we now recognise that urinary
caffeine levels have no practical utility as markers of a par-
ticular use of caffeine.
Second, the emerging evidence from studies over the past
decade is that performance benefits can be found with very
modest caffeine intakes (e.g., 2–3 mgkg–1 body mass, or
~100–200 mg caffeine) when caffeine is taken before and
(or) during exercise. Furthermore, there is no evidence of a
dose–response relationship to caffeine beyond this level of
intake — that is, performance benefits do not increase with
increases in the caffeine dose. One of the practical outcomes
of these newer findings is that athletes no longer need to
practise controlled doping (i.e., finding the largest dose of
caffeine that can be taken while keeping urinary caffeine
levels below 12 mgmL–1). Instead, performance benefits can
be found with caffeine intakes that are well within, or even
below, normal social uses. Such intakes of caffeine are
likely to be associated with very low urinary caffeine levels
in most athletes. In essence, there is no longer a distinction
between normal (social) caffeine intake and caffeine intake
that enhances performance.
Finally, there have been changes in the methods and in-
tentions of the major anti-doping programs. The World
Anti-Doping Agency (WADA) was created in 1999 as an in-
dependent international organization that promotes, coordi-
nates, and monitors the fight against doping in sport in all
its forms ( Following
work to harmonise anti-doping policies and rules among
sports and authorities, it took over the anti-doping work of
the International Olympic Committee and instituted its first
code and international standards on 1 January 2004. The
WADA Code is still based on a List of Prohibited Substan-
ces and Methods (see
ch2? However, the code has evolved
to include the possibility of ‘‘nonanalytical violations.’’ Ath-
letes (and their support staff) can be found guilty of a dop-
ing offence without a positive urine or blood test. Other
offences include the possession or admitted use of these pro-
hibited substances or methods.
The code that immediately preceded the institution of
the first WADA Code, the 2003 Olympic Movement Anti-
Doping Code, included caffeine within the category of
stimulants banned in competition, with an explanatory com-
ment that ‘‘for caffeine the definition of a positive is a con-
centration in urine greater than 12 mg/mL.’’ (International
Olympic Committee 2003) However, there are several inter-
pretations of the wording of this code. It could mean that
caffeine is a prohibited substance with the collary. Further-
more, it could mean that a urinary caffeine concentration >
12 mgmL–1 could serve as a reporting limit, and that all ob-
served or admitted uses of caffeine would constitute a
doping offence. Alternatively, it could mean that caffeine is
permitted at doses that produce urinary caffeine concentra-
tions < 12 mgmL–1. These interpretations have widely dif-
ferent and far-reaching outcomes. Indeed, there are a range
of different issues related to the different positions that caf-
feine could have in an anti-doping code, many of which
would create considerable practical challenges if imple-
mented (Table 8).
In fact, caffeine was removed from WADA’s List of Pro-
hibited Substances and Methods that came into effect on
1 January 2004, meaning that athletes could consume
caffeine, either in their background diets or for the specific
purposes of performance enhancement, without fear of
sanctions. However, it is currently still on the list of banned
drug classes of the National Collegiate Athletic Association,
the body governing college sport in the United States (http://
drug_testing/banned_drug_classes.pdf). Furthermore, caffeine
is part of the WADA monitoring program, meaning that caf-
feine concentrations are still measured in urine samples as a
means of detecting patterns of misuse in sport. This has al-
lowed some examination of the impact of the removal of caf-
feine from the prohibited list on caffeine use patterns by
athletes. Some recent studies have found a high prevalence of
caffeine use for perceived ergogenic effects among select
groups of athletes, such as Ironman triathletes (Desbrow and
Leveritt 2006) and British track and field athletes and cyclists
(Chester and Wojek 2008). However, measurement of over
4600 urine samples undertaken for doping control across
56 sports by a single laboratory in 2004 found no increase
in the mean caffeine concentration, compared with results
from 1993–2002 (Van Thuyne and Delbeke 2006). The
mean caffeine concentration in samples in 2004 was
1.12 mgmL–1, in comparison to a finding of 1.22 mgmL–1
from over 11 000 samples collected in 1993–2002 (Van
Thuyne et al. 2005). The 2004 study noted differences in
caffeine use among sports, with an increased average con-
centration and a larger percentage of higher urinary caf-
feine concentrations (defined as >4 mgmL–1) in cycling
and strength and (or) power sports than in other sports.
Cycling showed an apparent increase in the percentage of
higher urinary caffeine concentrations in 2004, while there
1330 Appl. Physiol. Nutr. Metab. Vol. 33, 2008
#2008 NRC Canada
Table 8. Examples of potential rulings regarding caffeine use in sport (Burke 2001).
Ruling Implications and issues
1. Caffeine is a prohibited substance in competition in absolute terms
Underpinning rationale: (i) caffeine
is a stimulant; (ii) caffeine intake
enhances sports performance;
(iii) caffeine is neither a nutrient
nor a necessary part of the diet.
Athletes would not be able to consume any tea, coffee, cola drinks, chocolate, etc., prior to and
during competition.
Strong education messages would be needed to convey this message and its implications to
The limit of urinary caffeine content would need to be set at very low levels. Although some
athletes would be able to consume caffeine and remain below this limit, a positive doping
offence would also be deemed to occur if the athlete was observed or admitted to consuming a
caffeine-containing product during the competition period.
Presumably, the difficulty in removing all caffeine from the normal diet would result in a large
number of positive doping offences.
Issues of possession and trafficking would need to consider the sale of tea, coffee, cola, and
chocolate at sporting venues, and the sponsorship of athletes, events, and sporting organizations
by companies that manufacture these products. These activities would need to be banned to be
consistent with the anti-doping code.
Even though caffeine intake would be banned in competition, athletes would still be able to
consume caffeine during training in a manner that provides a benefit to their performance and
adaptation to the training program.
2. Caffeine is a prohibited substance only when consumed in competition settings in doses that produce urinary caffeine levels
above a certain limit (to be determined)
Underpinning rationale: aurinary
caffeine limit can be set that
discriminates between social and
intentional use of caffeine, or at
least only picks up a few cases of
high caffeine use.
It is impossible to find a limit that distinguishes between social and intentional use of caffeine.
Caffeine intakes that produce a performance enhancement are indistinguishable from the
caffeine intakes reported by the normal population.
Urinary caffeine levels vary among and within individuals, and there is no standardization of the
collection of urine samples with regard to the timing between caffeine intake and sampling.
Therefore, urinary caffeine limits do not treat caffeine use equally.
Education messages to athletes could contain information about levels of caffeine intake that are
unlikely to produce a urinary caffeine level above this limit.
Athletes could not investigate their urinary caffeine concentrations in relation to various levels
of intake (trying to find how much caffeine they can take without producing a positive result for
caffeine doping), since this would be regarded as controlled doping.
Issues related to possession and trafficking of caffeine (as outlined in ruling 1) could still apply.
3. Caffeine is a prohibited substance only when intentionally consumed in competition settings in doses that produce urinary
caffeine levels above a certain limit (to be determined)
Underpinning rationale: a model
similar to drinking and driving
laws will prevent accidental cases
of high caffeine levels.
As in ruling 2, except that since urinary caffeine levels vary among individuals, and there is no
standardization of the collection of urine samples with regard to the timing between caffeine
intake and sampling, athletes should be allowed (or encouraged) to investigate what intakes of
caffeine can be tolerated without producing a positive test, without any penalty or prejudice. The
concept of controlled doping would not be applicable.
4. The prohibition on caffeine use in sport is removed
Underpinning factors: (i) caffeine is
so entrenched in the normal diet
that it is not practical to try to
achieve a ban on intake; (ii) there
is no unfair advantage if the
majority of athletes already
consume caffeine, and choose to
consume it for social reasons;
(iii) there are no health
disadvantages to the intake of
small amounts of caffeine; (iv) the
ergogenic benefits of caffeine on
performance, although worthwhile,
are small — they are similar in
magnitude to the effects of
consuming CHO during an
endurance event, but less than the
beneficial effects of consuming
fluid to minimize dehydration
Practical solution to overcome challenging situation.
Avoids tainting common foods and (or) drinks or common transactions in sport (e.g.,
sponsorship of companies that produce these products) with the odium of cheating.
Research should target the smallest dose of caffeine that can produce an ergogenic benefit.
Education messages to athletes could promote the message that, if they want to use caffeine
(socially or intentionally), small intakes produce maximal effects. Athletes would be encouraged
to reduce rather than increase their intake of caffeine, thus minimizing the health implications
and cost of using special products.
The market for specialized sports products containing caffeine might increase, unless education
messages (as above) remove the perceived benefits of large doses of caffeine or the need for
special food products.
Note: CHO, carbohydrate.
Burke 1331
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was a decrease in this outcome in swimming and basket-
ball. Overall, there was a decrease in the percentage of
urine samples showing caffeine concentrations below the
detectable range, and no increase in the percentage of sam-
ples with concentrations above 12 mgmL–1. In fact, only 6
samples were found with a concentration above the former
cutoff level (Van Thuyne and Delbeke 2006).
Further monitoring needs to take place before firm con-
clusions can be made. Nevertheless, it seems that there is lit-
tle evidence of systematic increases in the use or misuse of
caffeine at the highest levels of sport. One outcome of the
removal of caffeine from the prohibited list is the potential
for an increase in research activities and transparent educa-
tion about the benefits and disadvantages of caffeine use in
sport. Greater dissemination of the emerging information
that the benefits of caffeine occur at small to moderate
doses, and of the presence of individual variability and po-
tential side effects in response to caffeine intake, may ac-
tually lead to a reduction in caffeine use by athletes (e.g.,
lower doses being taken on fewer occasions). There is inad-
equate information about the total caffeine intakes of ath-
letes and recreational sportspeople and their patterns of
caffeine use. However, by choosing to withdraw caffeine in-
take before key events and by using the minimum ergogenic
doses during competition or training sessions, it is possible
that athletes will not consume more caffeine than the gen-
eral population, but rather, consume it in a more targeted
manner in relation to their sporting activities.
Caffeine is widely consumed from a variety of sources as
part of a normal diet, as well as in specialized sports foods
and supplements that may be used by athletes during train-
ing and competition. There is clear evidence that caffeine is
an ergogenic aid for a variety of types of sports, although
studies involving elite athletes and field situations are lack-
ing. Further research is needed to define the range of caf-
feine protocols and sports activities that show evidence of
performance enhancement, as well as the benefits or harm
to other issues underpinning recovery after exercise or prep-
aration for an event. Newer evidence suggests, at least in en-
durance sports, that the maximal benefits of caffeine are
seen at small to moderate caffeine doses (2–3 mgkg–1),
which are well within the normal daily caffeine intakes of
the general population. This makes the recent decision to re-
move caffeine from the list of prohibited substances in
sports a pragmatic choice. To date, there is little evidence
that this change has increased the use or misuse of caffeine
by athletes, at least within the levels of elite and subelite
sport, where anti-doping codes apply. Caffeine use may also
enhance the performance of sport in recreational athletes,
but it is inappropriate and unnecessary for use by young
adults. There is a need for strong and transparent education
to ensure that the correct messages about caffeine in sport
are provided to all athletes.
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... It was suggested that the potential effect of improvement after caffeine ingestion decreased with training experience since that athletes have reached their upper limits of exercise performance and physical conditioning [51,123]. However, it is likely that elite athletes have greater motivation to perform a fatiguing exercise and can provide more consistent performance day-today [124]. In this regard, it was reported that trained subjects have greater adenosine A 2a receptors than untrained ones [125]. ...
... In this way, it might be possible that the high density of adenosine receptors for elite athletes allows greater binding of caffeine to these receptors [122], which increases the level of performance enhancement following caffeine ingestion. Additionally, Burke [124] reported that the research sample may have an impact on the findings and that studies using just elite athletes would be most relevant. This is supported by the fact that more familiarity with training would lead to a lower degree of fluctuation, allowing modest changes in performance to be recorded with significance [124]. ...
... Additionally, Burke [124] reported that the research sample may have an impact on the findings and that studies using just elite athletes would be most relevant. This is supported by the fact that more familiarity with training would lead to a lower degree of fluctuation, allowing modest changes in performance to be recorded with significance [124]. Thus, there are inconsistent findings concerning the training level effect. ...
Full-text available
Although the effects of caffeine supplementation on combat sports performance have been extensively investigated, there is currently no consensus regarding its ergogenic benefits.This systematic review with meta-analysis aimed to summarize the studies investigating the effects of caffeine supplementation on different aspects of performance in combat sports and to quantitatively analyze the results of these studies to better understand the ergogenic effect of caffeine on combat sports outcomes. A systematic search for randomized placebo-controlled studies investigating the effects of caffeine supplementation on combat sports’ performance was performed through Scopus, Pubmed, Web of Science and Cochrane Library databases up to 18 April 2022. Random-effects meta-analyses of standardized mean differences (Hedge’s g) were performed to analyze the data. Twenty-six studies of good and excellent methodological quality (based on the Pedro scale) fulfilled the inclusion criteria. The meta-analysis results revealed caffeine has a small but evident effect size (ES) on handgrip strength (ES = 0.28; 95% CI: 0.04 to 0.52; p = 0.02), and total number of throws during the special judo fitness test (SJFT) (ES = 0.42; 95% CI: 0.06 to 0.78; p = 0.02). Regarding the physiological responses, caffeine increased blood lactate concentration ([La]) in anaerobic exercise (ES = 1.23; 95% CI: 0.29 to 2.18; p = 0.01) and simulated combat (ES = 0.91; 95% CI: 0.34 to 1.47; p = 0.002). For Heart Rate (HR), caffeine increased HR final (ES = 0.31; 95% CI: 0.11 to 0.52; p = 0.003), and HR 1min (ES = 0.20; 95% CI 0.004 to 0.40; p = 0.045). However, caffeine had no impact on the countermovement jump height, the SJFT index, the judogi strength-endurance test, the number and duration of offensive actions, HR at the end of the fight, and the rating of perceived exertion. Caffeine supplementation may be ergogenic for a range of combat sports aspects involving isometric strength, anaerobic power, reaction time, and anaerobic metabolism. However, supplementation effects might be ineffective under certain circumstances, indicating supplementation needs to take into account the performance metric in question prior to creating a dosing protocol.
... The performance-enhancing effects of acute caffeine ingestion have been explored at length, with well established benefits for endurance, intermittent, and resistance exercise [1,2] as well as low order cognitive functions [3]. More specifically, caffeine has been shown to improve physical and technical elements needed for successful soccer match play, with evidence indicating improved repeated sprint and jump performance [4], reactive agility [5], and passing accuracy [6]. ...
... Defensive Unity Reduction of the opposition's effective play-space. 1 Source: Teoldo et al. [20]. ...
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In soccer, physical, tactical, and decision-making processes are highly important facets of successful performance. Caffeine has well established effects for promoting both physical and cognitive performance, but the translation of such benefits specifically for soccer match play is not well established. This study examined the effects of acute caffeine ingestion on tactical performance during small-sided games (SSG) in professional soccer players. Nineteen soccer players (22 ± 4 yrs) underwent a randomized, counterbalanced, crossover, double-blind placebo-controlled trial. The protocol consisted of 5 bouts of 5-min SSG with 3 players plus a goalkeeper in each team (3 + GK × 3 + GK) with each SSG separated by 1 min rest intervals. Tactical performance was assessed using the system of tactical assessment in soccer (FUT-SAT). Prior to each experimental trial, participants ingested caffeine (5 mg·kg −1) or a placebo 60 min before the protocol. Overall, caffeine ingestion resulted in an increased ball possession time when compared to the placebo. When the offensive and defensive core principles were analyzed, the results were equivocal. Caffeine resulted in positive effects on some tactical decisions during the protocol, but it was deleterious or promoted no observed effect on other of the core tactical principles. Caffeine ingestion resulted in less offensive (during SSG3) and defensive (SSG 2, SSG3, and SSG4) errors. Caffeine ingestion also resulted in higher total offensive success during SSG 1 and SSG2, but it was detrimental during SSG3. Additionally, total defensive success was lower for the caffeine conditions during SSG 2 and SSG5 when compared to the placebo. In conclusion, caffeine influenced aspects of tactical decisions in soccer, resulting in fewer offensive and defensive errors, although it may be deleterious considering other tactical parameters. Future studies may clarify the effects of caffeine ingestion on specific decision-making parameters in soccer.
... MR is a strategy including the rinse of the solution in the mouth without swallowing it for 5-20 seconds and thus enabling to avoid the adverse side effects of the substance intake [34]. Caffeine ingestion may cause side effects such as tremor, nausea, irritability, anxiety, or gastrointestinal problems [29]; particularly, it is not recommended for young athletes due to those adverse effects on health [4], in some cases such as Ramadan, it is not preferred also due to different reasons [34]. Caffeine ingestion may not be recommended in some sports like archery. ...
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Study aim : The purpose of this study was to evaluate the acute effect of different four caffeine mouth rinse intervention (caffeinated coffee, decaffeinated coffee, placebo, control) on attention and hand-eye coordination. Material and methods : Sixty-five healthy, recreationally active female (n = 41) (age 22.89 ± 3.94 years; body mass index 20.87 ± 2.63 kg/m ² ) and male (n = 24) (age 29.91 ± 12.06 years; body mass index 22.56 ± 2.21 kg/m ² ) volunteered to participate in this randomized, single-blind, placebo-controlled, crossover study. The Stroop Color-Word Test (SCWT) and Mirror-Tracing Test (MTT) was used. Participants first completed a SCWT or MTT, then rinsed and expectorated 25 ml of caffeinated coffee (containing 0.13% caffeine) or decaffeinated coffee or placebo (water) or control that did not rinse for 10 s, followed by SCWT or MTT again. Data were analyzed using a 4 (mouth rinse interventions) × 2 (pre-test and post-test) repeated measures ANOVA. Results : SCWT time, MTT draw time and MTT number of error measures were not significantly different between four mouth rinse interventions (p > 0.05). Conclusions : Caffeinated coffee or decaffeinated coffee mouth rinse for 10 s provided immediately prior to SCWT or MTT did not affect attention and hand-eye coordination.
... Numerous pharmacological aids are used to counter the harmful effects of sleep loss, particularly caffeine. This substance is present in many dietary products including coffee, tea, chocolate, and soda (Burke 2008). The ability of caffeine to enhance cognitive and physical function is dose-dependent. ...
The present study aimed to assess the effects of repeated administration of low-dose caffeine during a night of total sleep deprivation on physical and cognitive performance. Twelve recreational runners (being non-habitual caffeine users) performed four test sessions in a double-blind randomized order after (i) a placebo or 6 mg/kg of caffeine ingestion during a baseline night (BN) or (ii) a placebo or three doses of 2 mg/kg of caffeine during a night of total sleep deprivation (TSD). At each session, they completed an exhaustive run at 75% of the final velocity in a Vameval test (Vvameval) around a 400 m outdoor athletics track and performed the correct detection and reaction time tasks. In comparison with BN, the TSD condition significantly impaired running performance, reaction time, and correct detections. On the contrary, caffeine intake improved exhaustive running performance after BN by 5.2% (p < .001) and after TSD by 8.9% (p < .001), increased correct detections after BN (p < .05) and TSD (p < .05), and decreased reaction time after BN (p < .01) and TSD (p < .05) compared to placebo. Therefore, the repeated ingestion of low-dose caffeine is an effective strategy to counteract the detrimental effects of total sleep deprivation on physical and cognitive performance.
... The list was composed of dietary products with high CAF content including different types of coffee, tea, energy drinks, cocoa products, popular beverages, medications and caffeine supplements. Previously published information and nutritional tables were used for database construction [26][27][28]. Based on the answers in FFQ, a qualified nutritionist estimated the habitual CAF intake. ...
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Introduction. The main goal of this study was to examine the effect of acute intake of 3 mg/kg/body mass (b.m.) of caffeine (CAF) on countermovement jump (CMJ) performance in recreationally trained women habituated to CAF. Material and Methods. 17 healthy recreationally trained women habitually using CAF participated in the study. The experiment followed randomized, cross-over, double-blind design under three different conditions: control test (CONT) or consumed placebo (PLAC) or consumed 3 mg/kg/b.m. of CAF (CAF-3). Each participant performed 2 sets of 2 CMJ. The following variables were recorded: concentric peak velocity (PV), peak power (PP) and jump height (JH). Results. The two-way repeated measure ANOVA (substance × set) revealed no statistically significant interaction and main effects for all measured variables between conditions. In comparison to the CONT and PLAC, the intake of CAF-3 was not effective at increasing PV (p = 0.533), JH (p = 0.417) and PP (p = 0.871) during 2 sets of the CMJ. Conclusions. This study suggests that 3 mg/kg/b.m. of CAF did not improve CMJ height in recreationally trained women habituated to CAF. Furthermore, the level of athletic performance might be considered a factor in regard to CAF ergogenicity.
... In healthy adults, caffeine enhances exercise and cognitive performance in studies with measures of acute or endurance exercise [9,23,53,62], and it is known that several parameters such as time of ingestion, dose or training status influence the efficacy of caffeine supplementation [7,49]. Intake of caffeine in a performance bar can significantly improve endurance performance and complex cognitive abilities during and after exercise [29], providing some information on a combinatorial effect in the human situation. ...
Full-text available
Regular physical activity has been associated with healthy brain aging, reflected by beneficial effects on cognition and learning and memory. Nutritional supplements such as caffeine have been shown to act as cognitive enhancers and may possess neuroprotective properties. Interestingly, caffeine also improves athletic capabilities and is widely used by athletes because of its performance-enhancing effect, while information on potential additive beneficial effects of physical activity and caffeine on cognitive performance is scarce. In the present study, the effects of caffeine supplementation in combination with prolonged physical and cognitive stimulation in the form of the enriched environment (EE) housing for a duration of 4 months were analyzed. We demonstrate that caffeine supplementation together with prolonged environmental enrichment led to enhanced memory function, resulting in improved recognition and spatial working memory in behavioral paradigms such as the novel object recognition task or the Morris water maze in C57Bl6 wild-type mice. Mice housed under EE conditions showed increased gene expression levels of brain-derived neurotrophic factor (BDNF) in the hippocampus. The present findings underscore the potential impact of continuous physical activity in the prevention of age-related cognitive decline and may offer new options for combinatorial approaches.
... In the general population, low caffeine doses are associated with few side effects. Nevertheless, higher doses (i.e., 6-9 mg/kg") usually lead to an increase in prevalence and magnitude of side effects [65]. Our data indicate that for most of the side effects analysed in the current systematic review, the dose-dependent response in the Fig. 2 Prevalence of caffeineassociated side effects according to caffeine dose in investigations that used a caffeine supplementation protocol to study the ergogenic effect of caffeine in athletes. ...
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Purpose The aim of this study was to systematically review evidence on the prevalence and magnitude of side effects associated with caffeine supplementation in athletes. Methods Systematic searches through the PubMed, VHL, Scopus, and Web of Science databases were conducted according to the PRISMA guidelines. Peer-reviewed articles written in English that reported the prevalence/percentage or magnitude/effect size of side effects after caffeine supplementation in athletes in a sports context were included. Studies were grouped by the dose of caffeine administered as follows: low = ≤ 3.0 mg/kg; moderate = from 3.1 to 6.0 mg/kg; high = ≥ 6.1 mg/kg. The magnitude of the side effects was calculated with effect sizes. Results The search retrieved 25 studies that met the inclusion/exclusion criteria with a pooled sample of 421 participants. The supplementation with caffeine produced a higher prevalence or magnitude of all side effects under investigation when compared to placebo/control situations. The prevalence (magnitude) was between 6 and 34% (ES between 0.13 and 1.11) for low doses of caffeine, between 0 and 34% (ES between −0.13 and 1.20) for moderate doses of caffeine, and between 8 and 83% (ES between 0.04 and 1.52) with high doses of caffeine. The presence of tachycardia/heart palpitations and the negative effects on sleep onset had the highest prevalence and magnitude, in athletes using supplementation with caffeine. Conclusion In summary, caffeine supplementation in the doses habitually used to enhance physical performance produces several side effects, both after exercise and at least 24 h after the ingestion. However, the prevalence and magnitude of side effects with high doses of caffeine were habitually higher than with low doses of caffeine. From a practical perspective, using ~3.0 mg/kg of caffeine may be the dose of choice to obtain the ergogenic benefits of caffeine with the lowest prevalence and magnitude of side effects.
... In contrast to high doses, low doses of caffeine produce minimal side effects (Spriet, 2014). Another aspect to consider is that low caffeine doses can be consumed even without targeted supplementation, as a caffeine dose of Effect of low caffeine doses 2 mg/kg for a 70 kg individual is equivalent to a caffeine dose in an energy drink, one to two cups of coffee or several cups of green tea (Burke, 2008). ...
Purpose – The aim of this review was to explore the effects of low doses of caffeine (<3 mg/kg) on jumping performance using a meta-analysis. Design/methodology/approach – The search for eligible studies was performed through six databases, with additional backward and forward citation tracking. A random-effects meta-analysis was performed to compare the effects of caffeine vs. placebo on jump height. The methodological quality of the included studies was appraised using the PEDro checklist. Findings – Eight studies were included in the review. They were classified as good or excellent methodological quality. The pooled number of participants across all studies was 203. Four studies provided caffeine in relative doses, ranging from 1 to 2 mg/kg. Four studies provided caffeine supplementation in absolute doses of 80, 150, or 200 mg. The meta-analysis found that caffeine ingestion increased vertical jump height (Cohen’s d: 0.21; 95% confidence interval: 0.10, 0.31; p < 0.001; +3.5%). Originality/value – The present meta-analysis found that caffeine doses of ∼1 to 2 mg/kg enhance jumping height. The effects observed herein are similar to those with higher caffeine doses, which is relevant as low caffeine doses produce minimal side effects. For most individuals, a caffeine dose of ∼1 to 2 mg/kg is equivalent to an amount of caffeine in an energy drink, one to two cups of coffee, one to two pieces of caffeinated chewing gum, or several cups of green tea.
Caffeine is a psycho-active stimulant that can improve physical and cognitive performance. We systematically reviewed the evidence on the effects of acute caffeine ingestion on physiological parameters, physical and technical-skill performance during high-performance team-sport match-play. Following PRISMA guidelines, studies were identified using scientific databases (PubMed, Web-of-Science, Scopus, and SPORTDiscus) in February 2021. Of 281 results, 13 studies met inclusion, totalling 213 participants. Included studies adopted the randomised double-blinded cross-over design, involving caffeine and control conditions. In studies reporting physiological variables, responses to caffeine included higher peak (n=6/ 8 [n/ total studies measuring the variable]) and mean (n=7/ 9) heart rates, increased blood glucose (n=2/ 2) and lactate (n=2/ 2) concentrations. Improvements in physical performance were widely documented with caffeine, including greater distance coverage (n=7/ 7), high-speed distance coverage (n=5/ 7) and impact frequencies (n=6/ 8). From three studies that assessed technical-skills, it appears caffeine may benefit gross-skill performance, but have no effect, or negatively confound finer technical-skill outcomes. There is compelling evidence that ingesting moderate caffeine doses (~3 to 6 mg·kg-1) ~60 minutes before exercise may improve physical performance in team-sports, whereas evidence is presently too scarce to draw confident conclusions regarding sport-specific skill performance.
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Caffeine is a common substance in the diets of most athletes and it is now appearing in many new products, including energy drinks, sport gels, alcoholic beverages and diet aids. It can be a powerful ergogenic aid at levels that are considerably lower than the acceptable limit of the International Olympic Committee and could be beneficial in training and in competition. Caffeine does not improve maximal oxygen capacity directly, but could permit the athlete to train at a greater power output and/or to train longer. It has also ben shown to increase speed and/or power output in simulated race conditions. These effects have been found in activities that last as little as 60 seconds or as long as 2 hours. There is less information about the effects of caffeine on strength; however, recent work suggests no effect on maximal ability, but enhanced endurance or resistance to fatigue. There is no evidence that caffeine ingestion before exercise leads to dehydration, ion imbalance, or any other adverse effects. The ingestion of caffeine as coffee appears to be ineffective compared to doping with pure caffeine. Related compounds such as theophylline are also potent ergogenic aids. Caffeine may act synergistically with other drugs including ephedrine and anti-inflammatory agents. It appears that male and female athletes have similar caffeine pharmacokinetics, i.e., for a given dose of caffeine, the time course and absolute plasma concentrations of caffeine and its metabolites are the same. In addition, exercise or dehydration does not affect caffeine pharmacokinetics. The limited information available suggests that caffeine non-users and users respond similarly and that withdrawal from caffeine may not be important. The mechanism(s) by which caffeine elicits its ergogenic effects are unknown, but the popular theory that it enhances fat oxidation and spares muscle glycogen has very little support and is an incomplete explanation at best. Caffeine may work, in part, by creating a more favourable intracellular ionic environment in active muscle. This could facilitate force production by each motor unit.
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Metabolic and ergogenic effects of carbohydrate and caffeine concentrations, common in commercial available beverages, were investigated in 16 tournament players (8 males and 8 females) during a 4 hrs interrupted tennis match (30 min rest after 150 min). On three double-blind occasions players ingested a placebo (PLA), carbohydrate (CHO) or caffeine drink (CAF) at court changeover and during the resting period. In men (women) total intake consisted of 2.8 l (2.0 l) fluid, supplemented with 243 g (182 g) carbohydrates (CHO) or with 364 mg (260 mg) caffeine (CAF), respectively. Postexercise all players performed a ball-machine test (BMT) and a tennis-sprint test (TST). During match play blood glucose (GLU) was higher in CHO and did not differ between CAF and PLA. Immediately after the resting period GLU temporary declined in CHO and PLA, while no significant changes occurred in CAF. Increases of serum FFA and glycerol as well as the decrease of insulin were similar during the PLA and CAF trials and less pronounced in CHO. Postexercise urine concentrations of epinephrine and caffeine were significantly higher in CAF. Perception ratings and hitting accuracy (BMT) were not affected by treatment. CHO resulted in higher blood lactate levels during match play and a better post-exercise sprint performance (TST). Under CAF women won significantly more games than during both other treatments. CHO enhances tennis-specific running-speed but has no ergogenic effect on tennis performance under the conditions of our study. CAF improves glucose homeostasis at the beginning of work load after rest and may increase tennis success in women.
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This investigation determined if 3 levels of controlled caffeine consumption affected fluid-electrolyte balance and renal function differently. Healthy males (mean standard deviation; age, 21.6 +/- 3.3 y) consumed 3 mg caffeine (.) kg(-1) (.) d(-1) on days I to 6 (equilibration phase). On days 7 to 11 (treatment phase), subjects consumed either 0 mg (CO; placebo; n = 20), 3 mg (C3; n = 20), or 6 mg (C6; n = 19) caffeine (.) kg(-1) (.) d(-1) in capsules, with no other dietary caffeine intake. The following variables were unaffected (P > 0.05) by different caffeine doses on days 1, 3, 6, 9, and 11 and were within normal clinical ranges: body mass, urine osmolality, urine specific gravity, urine color, 24-h urine volume, 24-h Na+ and K+ excretion, 24-h creatinine, blood urea nitrogen, serum Na+ and K+, serum osmolality, hematocrit, and total plasma protein. Therefore, C0, C3, and C6 exhibited no evidence of hypohydration. These findings question the widely accepted notion that caffeine consumption acts chronically as a diuretic.
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A study of a sample provides only an estimate of the true (population) value of an outcome statistic. A report of the study therefore usually includes an inference about the true value. Traditionally, a researcher makes an inference by declaring the value of the statistic statistically significant or nonsignificant on the basis of a P value derived from a null-hypothesis test. This approach is confusing and can be misleading, depending on the magnitude of the statistic, error of measurement, and sample size. The authors use a more intuitive and practical approach based directly on uncertainty in the true value of the statistic. First they express the uncertainty as confidence limits, which define the likely range of the true value. They then deal with the real-world relevance of this uncertainty by taking into account values of the statistic that are substantial in some positive and negative sense, such as beneficial or harmful. If the likely range overlaps substantially positive and negative values, they infer that the outcome is unclear; otherwise, they infer that the true value has the magnitude of the observed value: substantially positive, trivial, or substantially negative. They refine this crude inference by stating qualitatively the likelihood that the true value will have the observed magnitude (eg, very likely beneficial). Quantitative or qualitative probabilities that the true value has the other 2 magnitudes or more finely graded magnitudes (such as trivial, small, moderate, and large) can also be estimated to guide a decision about the utility of the outcome.
Recreational enthusiasts and athletes often are advised to abstain from consuming caffeinated beverages (CB). The dual purposes of this review are to (a) critique controlled investigations regarding the effects of caffeine on dehydration and exercise performance, and (b) ascertain whether abstaining from CB is scientifically and physiologically justifiable. The literature indicates that caffeine consumption stimulates a mild diuresis similar to water, but there is no evidence of a fluid-electrolyte imbalance that is detrimental to exercise performance or health. Investigations comparing caffeine (100-680 mg) to water or placebo seldom found a statistical difference in urine volume. In the 10 studies reviewed, consumption of a CB resulted in 0-84% retention of the initial volume ingested, whereas consumption of water resulted in 0-81% retention. Further, tolerance to caffeine reduces the likelihood that a detrimental fluid-electrolyte imbalance will occur. The scientific literature suggests that athletes a...
Conference Paper
Purpose: The purpose of this study was to assess research aimed at measuring performance enhancements that affect success of individual elite athletes in competitive events. Analysis: Simulations show that the smallest worthwhile enhancement of performance for an athlete in an international event is 0.7-0.4 of the typical within-athlete random variation in performance between events. Using change in performance in events as the outcome measure in a crossover study, researchers could delimit such enhancements with a sample of 16-65 athletes, or with 65-260 in a fully controlled study. Sample size for a study using a valid laboratory or field test is proportional to the square of the within-athlete variation in performance in the test relative to the event; estimates of these variations are therefore crucial and should be determined by repeated-measures analysis of data from reliability studies for the test and event. Enhancements in test and event may differ when factors that affect performance differ between test and event; overall effects of these factors can be determined with a validity study that combines reliability data for test and event. A test should be used only if it is valid, more reliable than the event, allows estimation of performance enhancement in the event, and if the subjects replicate their usual training and dietary practices for the study; otherwise the event itself provides the only dependable estimate of performance enhancement. Publication of enhancement as a percent change with confidence limits along with an analysis for individual differences will make the study more applicable to athletes. Outcomes can be generalized only to athletes with abilities and practices represented in the study. Conclusion: estimates of enhancement of performance in laboratory or field tests in most previous studies may not apply to elite athletes in competitive events.
The purpose of this study was to assess the influence of rehydration with a caffeinated beverage during nonexercise periods on hydration status throughout consecutive practices in the heat. Ten (7 women, 3 men) partially heat-acclimated athletes (age 24 +/- 1y, body fat 19.2 +/- 2%, weight 68.4 +/- 4.0 kg, height 170 3 cm) completed 3 successive days of 2-a-day practices (2 h/ practice, 4 h/d) in mild heat (WBGT = 23degreesC). The 2 trials (double-blind, random, cross-over design) included; 1) caffeine (CAF) rehydrated with Coca-Cola(R) and 2) caffeine-free (CF) rehydrated with Caffeine-Free Coca-Cola(R) Urine and psychological measures were determined before and after each 2-h practice. A significant difference was found for urine color for the post-AM time point, F = 5.526, P = 0.031. No differences were found among other variables (P > 0.05). In summary, there is little evidence to suggest that the use of beverages containing caffeine during nonexercise might hinder hydration status.
Recreational enthusiasts and athletes often are advised to abstain from consuming caffeinated beverages (CB). The dual purposes of this review are to (a) critique controlled investigations regarding the effects of caffeine on dehydration and exercise performance, and (b) ascertain whether abstaining from CB is scientifically and physiologically justifiable. The literature indicates that caffeine consumption stimulates a mild diuresis similar to water, but there is no evidence of a fluid-electrolyte imbalance that is detrimental to exercise performance or health. Investigations comparing caffeine (100-680 mg) to water or placebo seldom found a statistical difference in urine volume. In the 10 studies reviewed, consumption of a CB resulted in 0-84% retention of the initial volume ingested, whereas consumption of water resulted in 0-81% retention. Further, tolerance to caffeine reduces the likelihood that a detrimental fluid-electrolyte imbalance will occur. The scientific literature suggests that athletes and recreational enthusiasts will not incur detrimental fluid-electrolyte imbalances if they consume CB in moderation and eat a typical U.S. diet. Sedentary members of the general public should be at less risk than athletes because their fluid losses via sweating are smaller.
We investigate numerical simulations that utilize a nonlinear interdiffusion solver and dynamical x-ray diffraction calculations to predict the local composition evolution in low Ge concentration Si/SiGe superlattices and their diffraction patterns during annealing. Superlattice satellite peak decay rates are compared with experimentally measured values and simulated diffraction patterns are matched directly to data with good success. The simulations are used to test the sensitivity of x-ray diffraction to various uncertainties commonly encountered when measuring interdiffusion at Si/SiGe interfaces. It is found that the most serious errors result from variations in the Ge content across the surface of the wafer. For example, the resolution limit of most experimental techniques used to measure Ge concentration in a SiGe film is ±1 at. %, for a film with 11% mean Ge concentration annealed for 5 h at 870 °C, this level of error will cause the observed interdiffusivity values to deviate by −25% or +50%. The simulations are further used to show that for Si/SiGe interdiffusion, superlattice diffraction produces valid measurements when applied to 004 superlattice satellite peaks and square wave composition modulations even though it is only exactly applicable to satellite peaks about 000 reflections and to sinusoidal composition modulations. Finally, we show that proper interpretation of x-ray scattering data to extract Si/SiGe interdiffusivity values must account for the strong dependence of the interdiffusivity on Ge concentration. © 2003 American Institute of Physics.