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Placebo effect of caffeine in cycling performance.

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  • CHX Performance (London-England/Chamonix-France)

Abstract

BEEDIE, C. J., E. M. STUART, D. A. COLEMAN, and A. J. FOAD. Placebo Effects of Caffeine on Cycling Performance. Med. Sci. Sports Exerc., Vol. 38, No. 12, pp. 2159–2164, 2006. Purpose: The placebo effectVa change attributable only to an individual`s belief in the efficacy of a treatmentVmight provide a worthwhile improvement in physical performance. Although sports scientists account for placebo effects by blinding subjects to treatments, little research has sought to quantify and explain the effect itself. The present study explored the placebo effect in laboratory cycling performance using quantitative and qualitative methods. Method: Six well-trained male cyclists undertook two baseline and three experimental 10-km time trials. Subjects were informed that in the experimental trials they would each receive a placebo, 4.5 mgIkgj1 caffeine, and 9.0 mgIkgj1 caffeine, randomly assigned. However, placebos were administered in all experimental conditions. Semistructured interviews were also conducted to explore subjects` experience of the effects of the capsules before and after revealing the deception. Results: A likely trivial increase in mean power of 1.0% over baseline was associated with experimental trials (95% confidence limits, j1.4 to 3.6%), rising to a likely beneficial 2.2% increase in power associated with experimental trials in which subjects believed they had ingested caffeine (j0.8 to 5.4%). A dose– response relationship was evident in experimental trials, with subjects producing 1.4% less power than at baseline when they believed they had ingested a placebo (j4.6 to 1.9%), 1.3% more power than at baseline when they believed they had ingested 4.5 mgIkgj1 caffeine (j1.4 to 4.1%), and 3.1% more power than at baseline when they believed they had ingested 9.0 mgIkgj1 caffeine (j0.4 to 6.7%). All subjects reported caffeine-related symptoms. Conclusions: Quantitative and qualitative data suggest that placebo effects are associated with the administration of caffeine and that these effects may directly or indirectly enhance performance in well-trained cyclists. Key Words: EXPERIMENTAL DESIGNS, DECEPTIVE ADMINISTRATION, ERGOGENIC AIDS, BELIEF EFFECTS
Copyright @ 2006 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited.
Psychobiology and Behavioral Strategies
Placebo Effects of Caffeine
on Cycling Performance
CHRISTOPHER J. BEEDIE, ELIZABETH M. STUART, DAMIAN A. COLEMAN, and ABIGAIL J. FOAD
Canterbury Christ Church University, Canterbury, UNITED KINGDOM
ABSTRACT
BEEDIE, C. J., E. M. STUART, D. A. COLEMAN, and A. J. FOAD. Placebo Effects of Caffeine on Cycling Performance. Med. Sci.
Sports Exerc., Vol. 38, No. 12, pp. 2159–2164, 2006. Purpose: The placebo effectVa change attributable only to an individual`s
belief in the efficacy of a treatmentVmight provide a worthwhile improvement in physical performance. Although sports scientists
account for placebo effects by blinding subjects to treatments, little research has sought to quantify and explain the effect itself. The
present study explored the placebo effect in laboratory cycling performance using quantitative and qualitative methods. Method: Six
well-trained male cyclists undertook two baseline and three experimental 10-km time trials. Subjects were informed that in the
experimental trials they would each receive a placebo, 4.5 mgIkg
j1
caffeine, and 9.0 mgIkg
j1
caffeine, randomly assigned. However,
placebos were administered in all experimental conditions. Semistructured interviews were also conducted to explore subjects`
experience of the effects of the capsules before and after revealing the deception. Results: A likely trivial increase in mean power of
1.0% over baseline was associated with experimental trials (95% confidence limits, j1.4 to 3.6%), rising to a likely beneficial 2.2%
increase in power associated with experimental trials in which subjects believed they had ingested caffeine (j0.8 to 5.4%). A dose–
response relationship was evident in experimental trials, with subjects producing 1.4% less power than at baseline when they believed
they had ingested a placebo (j4.6 to 1.9%), 1.3% more power than at baseline when they believed they had ingested 4.5 mgIkg
j1
caffeine (j1.4 to 4.1%), and 3.1% more power than at baseline when they believed they had ingested 9.0 mgIkg
j1
caffeine (j0.4 to
6.7%). All subjects reported caffeine-related symptoms. Conclusions: Quantitative and qualitative data suggest that placebo effects
are associated with the administration of caffeine and that these effects may directly or indirectly enhance performance in well-trained
cyclists. Key Words: EXPERIMENTAL DESIGNS, DECEPTIVE ADMINISTRATION, ERGOGENIC AIDS, BELIEF EFFECTS
The placebo effect is a favorable outcome arising
purely from the belief that one has received a
beneficial treatment (4). It could be argued that in
relation to sports performance and research, the placebo
effect is widely acknowledged but little understood. Cer-
tainly, in common with practice in disciplines such as
medicine and clinical psychology, sports scientists account
for the possibility of a placebo effect in intervention studies
by using a placebo control condition. However, despite
evidence elsewhere that the placebo effect impacts a wide
range of physiological, psychological, and behavioral varia-
bles (6), the placebo effect per se has received scant
attention in sports science research. The few studies that
have specifically addressed the placebo effect in sport
(2,4,8,13), despite collectively providing little systematic
information relating to its magnitude or mechanisms, do
suggest that placebo effects might be associated with several
nutritional and pharmacological interventions. For example,
Clark et al. (4) reported placebo effects associated with
carbohydrate supplementation in cycling performance. Sub-
jects were allocated to three groups and were advised that
the carbohydrate group would probably show the most
improvement in performance. However, half of the carbo-
hydrate group was randomized to receive the placebo, and
half of the placebo group was randomized to receive the
carbohydrate. Those in the third group were informed,
correctly, that there was a 50:50 chance that their drink
would contain carbohydrate. Results indicated a difference
in mean power between the told-carbohydrate and told-
placebo groups of 3.8% (95% confidence/likely limits/range
= 0.2 to 7.9%).
Clark and colleagues made several recommendations for
future placebo-effect research, including the use of crossover
designs and the exploration of factors that might account for
individual differences in placebo responsiveness. The aim of
the present study was twofold: first, to use a crossover design
to investigate whether athletes given a placebo under the
impression it was a performance-enhancing substance would
perform at a higher level than in control conditions, and
Address for correspondence: Dr. Christopher J. Beedie, Department of
Sport Science, Tourism, and Leisure, Canterbury Christ Church Univer-
sity, Canterbury, CT1 1QU, UK; E-mail: c.j.beedie@canterbury.ac.uk.
Submitted for publication November 2005.
Accepted for publication June 2006.
0195-9131/06/3812-2159/0
MEDICINE & SCIENCE IN SPORTS & EXERCISE
Ò
Copyright Ó2006 by the American College of Sports Medicine
DOI: 10.1249/01.mss.0000233805.56315.a9
2159
Copyright @ 2006 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited.
secondly, to ascertain how the athletes themselves attributed
any perceived or observed changes in performance.
METHOD
Subjects. Institutional ethics approval and written
informed consent from all subjects were obtained. Subjects
were well-trained competitive male cyclists (N=7,age=30
T11 yr, height = 180 T6.3 cm, weight = 75 T5.1 kg)
recruited from local cycling teams. Before the performance
trials, and with the aim of catalyzing or reinforcing beliefs
about caffeine, subjects were provided with literature
reviewing the findings of published research into caffeine
and cycling performance and detailing anecdotal evidence
regarding the use of caffeine among elite cyclists. The
efficacy of this manipulation was assessed in poststudy
interviews. Initial analyses of experimental performance
trials indicated that the power output of subject 4 varied by
up to 20% between adjacent trials. His data were removed
from further statistical analysis, but his interview responses
are of interest and are reported below.
Procedure. Subjects each performed two 10-km
habituation trials and one V
˙O
2max
test on the SRM cycle
ergometer (Ingenieurburo Schoberer, Julich, Germany).
The SRM was set up to exactly replicate the subjects`
habitual riding position. Subjects performed five maximal-
effort 10-km time trials (each preceded by a standardized,
progressive 20-min warm-up), in the order of one
prebaseline (control), three experimental, and one
postbaseline (control). Subjects were informed that they
would perform one experimental trial in each of three
conditions: placebo, 4.5 mgIkg
j1
caffeine (moderate dose),
and 9.0 mgIkg
j1
caffeine (high dose), on a randomly
assigned double-blind basis. However, a deceptive
administration protocol (14) was employed: an identical
placebo capsule was administered in each experimental
trial. No caffeine was administered during the study.
Measures were power, oxygen uptake, heart rate, and
blood lactate concentration, taken every 2 km at the thumb.
Each of the trials was separated by a 3- to 10-d gap, and
the subjects were asked to maintain their usual training
and diet during the study but to refrain from heavy training
for 24 h before each trial. They were also asked not to
consume any caffeine after 6:00 p.m. the night before
testing to control for the effects of caffeine already con-
sumed (14).
Subjects in caffeine research might engage in an active
search for symptoms to identify to which experimental
condition they have been allocated (15). Recent research
has suggested that physical activity masks several of the
expected cognitive effects of caffeine (7). Thus, to ensure
that the integrity of the experimental deception was
maintained, capsules were not administered until the
subject was seated on the ergometer and pedaling.
To limit the potential for subjects to employ any pacing
strategies based on performance in previous trials, the only
performance-related feedback available to them during
trials was the distance they had covered. Similarly, to
preclude the possibility that knowledge of performance
data would contaminate post hoc attributions (e.g., the
attribution of a random increase in power to caffeine
irrespective of any real perceptions of caffeine effects),
feedback of all performance data was withheld until the
completion of the study.
Post hoc measures. Questionnaires were adminis-
tered after each experimental trial. Items included ‘‘Which
conditionVplacebo, low-dose caffeine, or high-dose
caffeineVdo you think you completed today?’’ ‘‘To
what extent did the capsule effect your performance’’
and ‘‘Did you experience any side effects?’’ Subjects were
reminded at this stage that they would complete only one
trial per condition. Although subjects were given the
opportunity to revise allocation of trial to condition at the
end of the experimental phase of the study, none chose to
do so.
Analyses. Performances in baseline trials were
averaged to estimate changes in treatment trials. Changes
in log-transformed mean power, oxygen uptake, lactate,
and heart rate between trials were analyzed using one-way
repeated-measures ANOVA. Recently, Batterham and
Hopkins (3) proposed the use of magnitude-based
inference, whereby the smallest worthwhile effect is
identified and justified, confidence limits are interpreted
in relation to this effect, and probabilities that the true
effect is beneficial, trivial, and/or harmful are derived.
Data below are presented in accordance with these
suggestions. Paton and Hopkins (16) have suggested that
the smallest practically beneficial improvement in
performance for a road cyclist is that equivalent to an
approximately 1.5% increase in power output; conse-
quently, this value was adopted as the threshold level for
the interpretation of confidence intervals.
The experimental design relied on a deceptive adminis-
tration protocol. Ethical guidelines of the American
Psychological Association (1) and our institutional ethics
committee required that subjects be thoroughly debriefed at
the conclusion of the data collection. The debrief process
was incorporated into poststudy interviews carried out in
the week after the final performance tests. Two semi-
structured interview schedules were prepared. Schedule 1,
delivered before revealing the results and the deception,
included questions such as ‘‘Did you expect caffeine to
effect your performance?’’ ‘‘What symptoms did you
experience?’’ and ‘‘Do you think that the caffeine affected
your performance?’’ Schedule 2, delivered after the results
and the deception had been revealed, investigated subjects`
previous responses in light of their knowledge that they
had received no caffeine. Interviews were conducted by the
first and second authors with one subject at a time in a
private office. Each interview lasted between 60 and 100 min,
and each was tape recorded with the subject`s permission. All
interviews were transcribed, and data were analyzed using
inductive content analysis as demonstrated by Jackson (9).
However, the resulting analysis seemed overly complex and
raised several themes, for example ‘‘trust in experimenters’
and ‘‘future use of caffeine,’’ which went beyond the scope
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of the present study. Subsequently, we adopted a less
analytical approach by summarizing responses relevant to
placebo effects.
RESULTS
Mean values by condition for all measured variables are
presented in Table 1. Mean and standard deviations for
percentage differences in power over baseline, confidence
intervals, and likelihood of worthwhile effects are
presented in Table 2. Interpretation of confidence intervals
revealed a likely trivial difference in power between pre-
and postbaseline trials, suggesting no systematic learning
or training effects. Overall, there was no practically
beneficial difference in power between mean baseline and
mean experimental conditions, although a dose–response
relationship was evident, with the placebo condition being
associated with a mean decrease in power compared with
baseline, whereas possibly beneficial and likely beneficial
increases in power were associated with the moderate- and
high-dose caffeine conditions, respectively. The within-
subject coefficient of variation (CV) for log-transformed
power was calculated at 2.7%. No substantial difference
was evident between the CV for baseline and for experi-
mental conditions.
Interpretation of 95% confidence intervals indicated no
substantial differences between mean baseline and either
mean experimental or mean caffeine conditions for heart
rate, oxygen uptake, and blood lactate.
Interview data (N= 7) indicated that five subjects
(subjects 1, 2, 3, 4, and 6) attributed direct performance
effects to the capsules, subject 5 was unsure whether to
attribute performance effects to the capsules, and subject 7
reported no performance effects (note that interview data
for subject 4 is included despite his experimental data
being removed from statistical analyses above). Perfor-
mance data were consistent with the interview data of five
subjectsVfor example, subjects 2 and 6, whose experi-
mental and interview data both suggest that they experi-
enced a placebo effect, subject 4, whose interview and
performance data arguably suggested a negative placebo or
‘nocebo’’ effect, and subject 7, whose experimental and
interview data both suggest that he did not experience a
placebo effect. Interview responses suggested three spe-
cific areas of interest; expectation of caffeine effects,
perceived effects of caffeine on performance, and potential
mechanisms.
Expectation of caffeine effects. Four subjects
(subjects 1, 2, 3, and 4) indicated that they expected the
capsules to have a positive effect on their performance.
However, no clear relationship between belief in caffeine
and performance emerged. For example, subject 6, whose
performance data suggested that he experienced a
significant placebo response and who subsequently
indicated that he believed this to be the case, reported
very low a priori expectation of caffeine effects. Subject 4,
however, indicated that he was expecting caffeine ‘‘to have
a mega effect’’ and went on to describe how, on the basis
of symptoms experienced during what he believed was the
high-dose caffeine trial, he was unable to complete it,
stating ‘‘I felt terrible, that must have been the big dose of
caffeine.’’ It is possible that this poor performance may
have resulted from illness.
Effects on performance. Five subjects (subjects 1, 2,
3, 4, and 6) reported direct effects of caffeine on
performance. Subject 1 reported that during certain tests,
‘it got to the point at which on the previous test you really
[feel] the pain to the legs and you start to go down a bit, on
another test I got to that stage but then I lifted again,’’ and
‘you get a bit more aggressive you sort of pick up the rpm
again and you think to yourself, Fthis must be the
caffeine.`’ Subject 2 suggested, ‘‘when I thought I was
on the 9 mg of caffeine I went faster, I felt more on top of
it whereas all the other times I felt like I was having to dig
in just to keep the pedals turning over. I think I was
pushing a bigger gear than normal, I was able to push
harder with less pain.’’ Subject 6 suggested, ‘‘the first time
I had the tablet was definitely an improvement on the
[trial] before. I was surprised actually how different it felt,
whether that was [the tablets] or not I still obviously don`t
know, but certainly that first tablet I took I thought, Fwell,
this is a damn sight easier than it was last time.`’’ H e
suggested that during experimental trials, ‘‘it was easier to
put the effort in, there wasn`t any tiredness creeping in, I
was actually expecting to start feeling tired at a particular
point normally after about 10 min on the bike and it didn`t
so you think Foh great, well I`ll press a little bit harder and
I`ll go a little bit faster.`’’ Subject 7 suggested, ‘‘one
particular day when I turned up and did it I felt really
zippy, you pedal and you pedal hard and you`re out of
breath but you feel you can ride at that threshold and a
little bit higher,’’ but this subject also added, ‘‘whether it
was because of the caffeine, I don`t know.’’
Placebo mechanisms. Six subjects (all except
subject 7) suggested potential placebo-effect mechanisms.
TABLE 1. Means and standard deviations for power output, blood lactate, oxygen
uptake, and heart rate by condition (N= 6).
Power
(W)
Lactate
(mM)
V
˙O
2
(mLIkg
j1
Imin
j1
)
Heart Rate
(bpm)
Pre baseline 276.6 (39.1) 10.7 (1.5) 57.8 (9.0) 178.1 (10.1)
Placebo 274.3 (46.3) 10.5 (3.3) 60.2 (8.2) 169.2 (14.4)
4.5 mgIkg
j1
280.6 (37.1) 10.8 (2.5) 56.8 (11.0) 172.4 (13.9)
9.0 mgIkg
j1
285.9 (38.7) 11.3 (2.7) 57.8 (10.8) 171.4 (14.2)
Post baseline 278.9 (41.0) 10.7 (3.1) 58.0 (8.8) 172.4 (14.7)
Mean baseline 277.7 (42.3) 10.7 (2.3) 57.9 (8.8) 172.2 (12.2)
Mean experimental 280.3 (40.5) 10.9 (2.7) 58.3 (9.7) 171.0 (13.9)
Mean caffeine 283.2 (37.8) 11.0 (2.7) 58.8 (9.7) 171.94 (14.0)
TABLE 2. Mean and SD percentage differences in power over baseline, confidence
intervals, and practical significance of effects (N= 6).
Percent Change over
Mean Baseline (%) 95% CI
Percent Chance That
Effect is Beneficial
(Mean [SD]) (Lower to Upper) (Trivial/Harmful)
Mean experimental 1.0 (2.4) j1.4 to 3.6 34 (64/2)
Placebo j1.4 (3.1) j4.6 to 1.9 4 (51/46)
4.5 mgIkg
j1
1.3 (2.7) j1.4 to 4.1 45 (53/2)
9.0 mgIkg
j1
3.1 (3.4) j0.4 to 6.7 86 (13/1)
Mean caffeine 2.2 (3.0) j0.8 to 5.4 72 (26/1)
PLACEBO EFFECTS IN CYCLING PERFORMANCE Medicine & Science in Sports & Exercise
d
2161
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These explanations fell into four broad categories: a) pain
reduction(sixsubjects)Vfor example, ‘‘the pain went
away,’’ ‘‘I don`t think there was so much pain,’’ ‘‘It`s not
that you feel it more or less you can just tolerate [pain] a bit
more,’’ ‘‘I was able to push harder with less pain,’’ and
‘[you can ride] without it hurting and that`s the difference’’;
b) belief–behavior relationships (four subjects)Vfor
example, ‘‘because you think that you`ve taken caffeine,
there must be something in the brain that might tell
you`ve taken something that`s gonna make you go better
so it does,’’ ‘‘there is this great big tablet and you think
Fthere must be a huge dose in there therefore this is
gonna do something really good`and perhaps just that
pure belief or hope that it was gonna do something did do
something,’’ and ‘‘you just believe that it`s gonna make
you stronger and you believe in it enough to actually
make you stronger, so you try to bring yourself up to the
level of the difference that it`s supposed to make, you
actually raise your game to try and match the tablet’’; c)
attentional changes (two subjects)Vfor example, ‘‘you`re
focusing on something else that`s helping you so it
actually takes your attention away from hurting so
much`’; and d) arousal changes (two subjects)Vfor
example, ‘‘it calms you because you know you are
getting something to help youII tend to ride better if
I`m more relaxed. In my jobVI`m a firemanVyou`ve
only got this air on the back and that`s all you`ve got.
When you go into a lighted [building], if you keep calm
as you can you use less air, so you`re more efficient if
you`re more calm.’
DISCUSSION
When subjects were administered a placebo capsule they
believed to be caffeine, they produced, on average,
substantially greater power than at baseline. Furthermore,
effects were stronger when subjects believed they had
ingested higher doses of caffeine. The coefficient of
variation for power was comparable with previous research
on elite cyclists (15) and lower than for several current lab-
based cycle performance tests (5), suggesting that the
observed effects are unlikely to be the results of random
biological or mechanical variations. Using recently pub-
lished criteria (16), we are able to state that the effects
observed are likely to be of practical benefit to a road
cyclist in competition. Furthermore, some of these effects
are similar in magnitude to those attributed to caffeine in
several published performance studies (19).
Subjects in the present study had a 67% expectation of
caffeine ingestion. Had we adopted a design that more
closely replicated real-life drug-administration protocols,
that is, a deceptive no-blind design in which subjects had a
100% expectation of caffeine administration, we might
have expected performance effects of greater magnitude.
Use of such a design might also have permitted us a greater
degree of confidence in stating that observed effects
resulted directly from the intervention (i.e., they were
placebo effects) and not from a process whereby a subject
simply felt good on one or more days and attributed those
feelings to the effects of ingested caffeine. We acknowl-
edge that the potential for subjects to attribute random
changes in performance to the ingestion of caffeine was a
limitation of the experimental design. However, a secon-
dary aim of the present study was to investigate the
mechanisms underlying subjects`attribution of trial to
condition, and therefore we aimed to leave subjects in
some doubt as to whether they had ingested caffeine in any
one trial. It was anticipated that subsequent interview data
might elucidate the mechanisms underlying subjects`
allocation of trial to condition. To a certain extent, this
approach was fruitful. For example, two subjects indicated
that because they believed they had already received
caffeine in the first and second experimental trials, they
had low or zero expectation of caffeine administration in
the third (subject 2 suggested, ‘‘maybe going into the final
day having had a really fast day and one relatively fast
makes you think Fhang on a second you can`t be given
caffeine again`’’). This finding suggests that subjects`
assumptions about what has or has not been administered
in previous trialsVplacebo or drugVmight influence
performance in subsequent trials.
Potential placebo mechanismsVfor example, whether
the placebo effect is manifest as a direct effect on
performance or whether a subject`s awareness of caffeine
symptoms leads to a revised pacing strategy and, thereby,
enhanced performanceVare of some significance to sports
performance research. In this respect, it is interesting that
ANOVA revealed no differences between baseline and
experimental conditions in any measured physiological
variables, which suggests that changes in performance may
not have been the result of deliberate changes in pace (this
finding, however, might also be a statistical anomaly
resulting from the small sample and the fact that the CV
for these indices are usually somewhat higher than those
for power (5)). It is certainly logical to argue that an athlete
performing at volitional maximal power output would
not be able to revise his or her pacing strategy and
produce still greater power on becoming aware of the
subjective symptoms of caffeine ingestion. Conversely,
an athlete performing below maximal volitional power
output may, on becoming aware of such symptoms, use
these as a cue to revise a pacing strategy and produce
greater power. Certainly, subjects in the present study
reported both perceived caffeine symptoms as well as
perceived direct effects on performance. Each subject
volunteered at least one caffeine symptom, and some-
what surprisingly, even after being informed of the
deception, none of the subjects reappraised these percep-
tions. This pattern of responses may, as Kienle and
Kiene (10) suggest, simply demonstrate a desire to please
the researchers. However, we argue that, on the basis of
previous research in psychology and medicine using
substances such as painkillers, alcohol, and caffeine, the
most parsimonious explanation is that individuals tend to
experience symptoms consistent with those of the sub-
stance they believe they have ingested.
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Interestingly, subjects 5 and 7, who reported the fewest
caffeine-related symptoms and the least confidence in
having experienced a placebo effect, also produced the
highest mean power overall. Subject 6, who produced
lowest mean power overall, reported arguably the largest
and least ambiguous placebo effect. These findings hint
at a relationship between training status and placebo
responsiveness, as suggested in previous sports perfor-
mance research (4).
Five subjects attributed direct performance effects to the
capsules, one was unsure whether to attribute performance
effects to the capsules, and one reported no performance
effects. As stated above, performance data are consistent
with the interview data of some subjects and less so with
others. This is not necessarily surprising, because we can
never be sure, even if one subject`s mean baseline and
mean experimental speeds are similar, that a placebo effect
did not bring up to par one or more experimental perfor-
mances that would otherwise have been below par, or vice
versa. Similarly, it is possible that a subject, recognizing
symptoms of caffeine ingestion, may have revised his
pacing strategy accordingly and increased his power
output, but to such a degree that he fatigued prematurely,
resulting in a below-par performance overall. It should also
be remembered that all interview responses are based on
two somewhat unreliable processes, human perception and
human recall; no amount of triangulation will unravel that
particular problem.
All subjects proposed at least one possible mechanism
that might explain observed placebo effects, and each of
these, at one level or another, involved belief. Proposals
varied from the vague (e.g., ‘‘something in the brain’’) to
the specific, such as endorphin-driven pain reduction. (The
latter proposal, placebo analgesia, a potential mechanism
that was suggested by all subjects in the present study, is
currently attracting considerable attention in contemporary
medical research and practice (6).) An interesting mecha-
nism was proposed by subject 5, a firefighter, who
described how the placebo effect might operate by
enabling him to feel less anxious and thus enable his
cardiorespiratory and musculoskeletal systems to function
more efficiently, producing greater work at a given
metabolic cost. Such a mechanism might theoretically not
be associated with any changes in physiological parameters
such as oxygen uptake or blood lactate and could explain
the lack of any observed changes in such variables in the
present study.
In summary, once a subject is informed that he or she is
to be given a substance that will enhance performance,
several subject- or environment-specific psychological
processes, such as belief, pain sensation, expectancy, and
arousal may be modified. Each of these processes might
have an impact on performance depending on its
respective direction, intensity, and valence. It is reason-
able to suggest that these processes might also be
modified on the basis of new information or feedback
once performance is under way. Thus, the search for the
mechanisms underlying the placebo effect will likely be a
complex process. Experimental designs that seek not only
to demonstrate the effect but also to provide some
explanation are required. Kirsch and Weixel (11), having
demonstrated empirically that a double-blind protocol
reduced the magnitude of placebo effects in relation to
deceptive no-blind conditions, suggested: ‘‘If double-blind
administration produces psychological effects that in
some instances are opposite to those produced by clinical
administration of drugsIthen double-blind procedures
may not be appropriate methods by which to evaluate
drug effects’’ (p. 323). Despite the requirement for either
more subjects or more trials per subject, the use of no-
placebo controls alongside placebo and experimental
conditions, or of deceptive no-blind conditions (e.g., the
balanced placebo design (14)) would give sports scientists
more insight into the mechanisms underlying many
interventions. Such approaches might also be used to
investigate the intuitively appealing proposal that placebo
and pharmacological/nutritional effects do not act in
isolation but, rather, combine in either an additive or
interactive way. It is reasonable to suggest that researchers
should also examine the impact of belief on performance,
either controlling for, or treating as independent variables,
the beliefs of subjects in intervention studies. Such
strategies might provide a clearer picture of the mecha-
nisms underlying the ergogenic effects of many commer-
cially available products and, in doing so, might allow
athletes and sports science professionals alike to make
more well-informed decisions in relation to the use of such
products.
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http://www.acsm-msse.org2164 Official Journal of the American College of Sports Medicine
... We approached the placebo intervention with a placebo- deceived design as others have previously argued that the use of double-blind designs is a possible source of bias in clinical trials and sports nutrition studies (Kirsch and Weixel, 1988;Saunders et al., 2016). In fact, some have reported that performance outcomes in physical tests are negatively affected if participants identify the presence of a PLA intervention ( Beedie et al., 2006;Foad et al., 2008). Therefore, similar to designs reported elsewhere we informed participants of the presence of a PLA substance only when they concluded the participation in the study ( Beedie et al., 2006;Foad et al., 2008). ...
... In fact, some have reported that performance outcomes in physical tests are negatively affected if participants identify the presence of a PLA intervention ( Beedie et al., 2006;Foad et al., 2008). Therefore, similar to designs reported elsewhere we informed participants of the presence of a PLA substance only when they concluded the participation in the study ( Beedie et al., 2006;Foad et al., 2008). An investigator, unaware of the supplement given to participants, provided verbal encouragement during all MIT exercises. ...
... Results of the present study provide important insights regarding the use of double-blind designs in sports nutrition studies. Some suggested that double-blind designs are a possible source of bias in randomized trials ( Kirsch and Weixel, 1988;Saunders et al., 2016), as performance outcomes on motor tests are influenced when participants identify the presence of a PLA intervention ( Beedie et al., 2006;Foad et al., 2008). The use of a PLA-deceived design in the present study may have overestimated the PLA effects normally observed when participants are told they have a 50% chance of ingesting the actual active substance in a typical double-blind design (Vase et al., 2002). ...
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Caffeine (CAF) is an ergogenic aid used to improve exercise performance. Independent studies have suggested that caffeine may have the ability to increase corticospinal excitability, thereby decreasing the motor cortex activation required to generate a similar motor output. However, CAF has also been suggested to induce a prefrontal cortex (PFC) deoxygenation. Others have suggested that placebo (PLA) may trigger comparable effects to CAF, as independent studies found PLA effects on motor performance, corticospinal excitability, and PFC oxygenation. Thus, we investigated if CAF and CAF-perceived PLA may improve motor performance, despite the likely unchanged MC activation and greater PFC deoxygenation. Nine participants (26.4 ± 4.8 years old, VO2MAX of 42.2 ± 4.6 mL kg-1 min-1) performed three maximal incremental tests (MITs) in control (no supplementation) and ∼60 min after CAF and PLA ingestion. PFC oxygenation (near-infrared spectroscopy at Fp1 position), MC activation (EEG at Cz position) and vastus lateralis and rectus femoris muscle activity (EMG) were measured throughout the tests. Compared to control, CAF and PLA increased rectus femoris muscle EMG (P = 0.030; F = 2.88; d = 0.84) at 100% of the MIT, and enhanced the peak power output (P = 0.006; F = 12.97; d = 1.8) and time to exhaustion (P = 0.007; F = 12.97; d = 1.8). In contrast, CAF and PLA did not change MC activation, but increased the PFC deoxygenation as indicated by the lower O2Hb (P = 0.001; F = 4.68; d = 1.08) and THb concentrations (P = 0.01; F = 1.96; d = 0.7) at 80 and 100% the MIT duration. These results showed that CAF and CAF-perceived PLA had the ability to improve motor performance, despite unchanged MC activation and greater PFC deoxygenation. The effectiveness of CAF as ergogenic aid to improve MIT performance was challenged.
... Increases in this subgroup were likely beneficial, above the variation in the test (+3.7 vs +3.0%) and very close to the overall beneficial effect of caffeine shown in this study (~4.0%). Beedie et al. (2006) previously investigated the effects of expectation on performance; participants were informed that they had ingested either 4.5 or 9.0 mg/kgBM of caffeine prior to exercise although caffeine was not administered on any occasion. Despite this, the authors showed a likely beneficial 2.2% in 10 km TT performance when participants believed they had ingested caffeine, which is similar to the performance increase of ~3.5% according to post-exercise caffeine identification in PLA in this study. ...
... Post-exercise, incorrect placebo identification fell below this overall improvement (+3.3%) while correct identification of caffeine improved further (+6.5%). These changes are due to a number of participants changing their opinion from pre-to post-exercise, likely due to stimuli relating to the exercise ( Beedie et al., 2006). The majority of the stated reasons for believing caffeine had been ingested prior to exercise were due to the sensation of caffeine associated side-effects, specifically tachycardia, alertness and trembling. ...
... Furthermore, it cannot be fully elucidated whether any participant's change in supplement identification resulted from their performance or whether it shaped the performance itself. Nonetheless, these data support the notion that preconceptions may be further modified by factors intrinsic to exercise ( Beedie et al., 2006), and thus should be taken into account. Future research should include pre-and post-exercise questionnaires including the opportunity to discuss why opinions were modified. ...
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We investigated the effects of supplement identification on exercise performance with caffeine supplementation. Forty-two trained cyclists (age 37 ± 8 years, body mass [BM] 74.3 ± 8.4 kg, height 1.76 ± 0.06 m, maximum oxygen uptake 50.0 ± 6.8 mL/kg/min) performed a ~30 min cycling time-trial 1 h following either 6 mg/kgBM caffeine (CAF) or placebo (PLA) supplementation and one control (CON) session without supplementation. Participants identified which supplement they believed they had ingested (“caffeine”, “placebo”, “don't know”) pre- and post-exercise. Subsequently, participants were allocated to subgroups for analysis according to their identifications. Overall and subgroup analyses were performed using mixed-model and magnitude-based inference analyses. Caffeine improved performance vs PLA and CON (P ≤ 0.001). Correct pre- and post-exercise identification of caffeine in CAF improved exercise performance (+4.8 and +6.5%) vs CON, with slightly greater relative increases than the overall effect of caffeine (+4.1%). Performance was not different between PLA and CON within subgroups (all P > 0.05), although there was a tendency toward improved performance when participants believed they had ingested caffeine post-exercise (P = 0.06; 87% likely beneficial). Participants who correctly identified placebo in PLA showed possible harmful effects on performance compared to CON. Supplement identification appeared to influence exercise outcome and may be a source of bias in sports nutrition.
... The beneficial effects of placebos on motor performance have also been demonstrated in cycling and running (Beedie, Coleman, & Foad, 2007;Beedie, Stuart, Coleman, & Foad, 2006;Clark, Hopkins, Hawley, & Burke, 2000;Foster, Felker, Porcari, et al., 2004;McClung & Collins, 2007). Clark et al. (2000) evaluated the effects of real and placebo supplement of carbohydrates on the resistance capacity of athletes in a 40-km cycling race. ...
... Moreover, the amount of active ingredient that participants think is present in the placebo substance can differentially modulate the placebo effect in motor performance. This phenomenon was demonstrated by Beedie et al. (2006) in well-trained cyclists who were tested in a simulation of a 10-km race. The cyclists were told about the efficacy of caffeine in improving motor performance and were then tested in three experimental conditions in which they expected they'd receive either an inert substance or different doses of caffeine (4.5 or 9.0 mg/kg). ...
Chapter
There is strong behavioral evidence that placebo and nocebo effects can influence aspects of motor performance like speed, force, and resistance to fatigue in athletes and non-athletes alike. These behavioral studies were essential for extending experimental investigation of the placebo and nocebo effects from the pain to the motor domain and to reveal how verbal suggestions and experiential learning are involved in shaping modulatory systems and related behavioral responses. However, the neural underpinnings of these effects in the motor domain are still largely unknown. Studies in healthy subjects demonstrated that the placebo-induced enhancement of force is associated with increased activity in the corticospinal system and that the placebo-induced reduction of fatigue can be disclosed by recording the readiness potential, an electrophysiological sign of movement preparation. Further evidence derives from studies in patients with Parkinson's disease that have directly demonstrated that placebo-induced improvements in motor symptoms are related to changes in subcortical neural firing activity and dopamine release. Future investigations are needed to better clarify the complex neural architecture underpinning the placebo and nocebo effects in the motor domain.
... We have previously shown that expectancy associated with caff eine supplementation may modify the ergogenic eff ect of both the active intervention and the placebo session 30 . Other studies have also demonstrated the ergogenic potential of expectancy with caff eine supplementation 31 . Th us, the current data suggest that part of the ergogenic eff ect shown here with caff eine supplementation may be due to the placebo eff ect, although the placebo trial was not improved compared to the control. ...
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Caffeine has been shown to increase anaerobic energy contribution during short-duration cycling time-trials (TT) though no information exists on whether caffeine alters energy contribution during more prolonged, aerobic type TTs. The aim of this study was to determine the effects of caffeine supplementation on longer and predominantly aerobic exercise. Fifteen recreationally-trained male cyclists (age 38±8 y, height 1.76±0.07 m, body mass 72.9±7.7 kg) performed a ~30 min cycling TT following either 6 mg·kg-1BM caffeine (CAF) or placebo (PLA) supplementation, and one control (CON) session without supplementation, in a double- -blind, randomised, counterbalance and cross-over design. Mean power output (MPO) was recorded as the outcome measure. Respiratory values were measured throughout exercise for the determination of energy system contribution. Data were analysed using mixed-models. CAF improved mean MPO compared to CON (P=0.01), and a trend towards an improvement compared to PLA (P=0.07); there was no difference in MPO at any timepoint throughout the exercise between conditions. There was a main effect of Condition (P=0.04) and Time (P<0.0001) on blood lactate concentration, which tended to be higher in CAF vs. both PLA and CON (Condition effect, both P=0.07). Ratings of perceived exertion increased over time (P<0.0001), with no effect of Condition or interaction (both P>0.05). Glycolytic energy contribution was increased in CAF compared to CON and PLA (both P<0.05), but not aerobic or ATP-CP (both P>0.05). CAF improved aerobic TT performance compared to CON, which could be explained by increased glycolytic energy contribution.
... The placebo effect, defined as a change attributable only to an individual's belief in the efficacy of treatment, has been demon- strated to improve physical performance in well-trained male cy- clists ( Beedie et al. 2006) and in untrained healthy males ( Pollo et al. 2008) who believed they had ingested caffeine but were actually administered placebo. Surprisingly, in our female partic- ipants, but not in our male participants, a stronger belief that they had been administered caffeine was associated with a lower en- durance capacity. ...
Article
Acute caffeine ingestion is considered effective in improving endurance capacity and psychological state. However, current knowledge is based on the findings of studies that have been conducted on male subjects mainly in temperate environmental conditions, but some physiological and psychological effects of caffeine differ between the sexes. The purpose of this study was to compare the physical performance and psychological effects of caffeine in young women and men exercising in the heat. Thirteen male and 10 female students completed 2 constant-load walks (60% of thermoneutral peak oxygen consumption on a treadmill until volitional exhaustion) in a hot-dry environment (air temperature, 42 °C; relative humidity, 20%) after caffeine (6 mg·kg(-1)) and placebo (wheat flour) ingestion in a double-blind, randomly assigned, crossover manner. Caffeine, compared with placebo, induced greater increases (p < 0.05) in heart rate (HR) and blood lactate concentrations in both males and females but had no impact on rectal or skin temperatures or on walking time to exhaustion in subjects of either gender. Caffeine decreased (p < 0.05) ratings of perceived exertion and fatigue in males, but not in females. In females, but not in males, a stronger belief that they had been administered caffeine was associated with a shorter time to exhaustion. In conclusion, acute caffeine ingestion increases HR and blood lactate levels during exercise in the heat, but it has no impact on thermoregulation or endurance capacity in either gender. Under exercise-heat stress, caffeine reduces ratings of perceived exertion and fatigue in males but not in females.
... The placebo effect, defined as a change attributable only to an individual's belief in the efficacy of treatment, has been demonstrated to improve physical performance in well-trained male cyclists (Beedie et al. 2006) and in untrained healthy males (Pollo et al. 2008) who believed they had ingested caffeine but were actually administered placebo. Surprisingly, in our female participants, but not in our male participants, a stronger belief that they had been administered caffeine was associated with a lower endurance capacity. ...
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