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Abstract

Purpose: The purpose of this study was to determine the oral dose of caffeine needed to increase muscle force and power output during all-out single multijoint movements. Methods: Thirteen resistance-trained men underwent a battery of muscle strength and power tests in a randomized, double-blind, crossover design, under four different conditions: (a) placebo ingestion (PLAC) or with caffeine ingestion at doses of (b) 3 mg · kg(-1) body weight (CAFF 3mg), (c) 6 mg · kg(-1) (CAFF 6mg), and (d) 9 mg · kg(-1) (CAFF 9mg). The muscle strength and power tests consisted in the measurement of bar displacement velocity and muscle power output during free-weight full-squat (SQ) and bench press (BP) exercises against four incremental loads (25%, 50%, 75%, and 90% one-repetition maximum [1RM]). Cycling peak power output was measured using a 4-s inertial load test. Caffeine side effects were evaluated at the end of each trial and 24 h later. Results: Mean propulsive velocity at light loads (25%-50% 1RM) increased significantly above PLAC for all caffeine doses (5.4%-8.5%, P = 0.039-0.003). At the medium load (75% 1RM), CAFF 3mg did not improve SQ or BP muscle power or BP velocity. CAFF 9mg was needed to enhance BP velocity and SQ power at the heaviest load (90% 1RM) and cycling peak power output (6.8%-11.7%, P = 0.03-0.05). The CAFF 9mg trial drastically increased the frequency of the adverse side effects (15%-62%). Conclusions: The ergogenic dose of caffeine required to enhance neuromuscular performance during a single all-out contraction depends on the magnitude of load used. A dose of 3 mg · kg(-1) is enough to improve high-velocity muscle actions against low loads, whereas a higher caffeine dose (9 mg · kg(-1)) is necessary against high loads, despite the appearance of adverse side effects.
Neuromuscular Responses to Incremental
Caffeine Doses: Performance and Side Effects
JESU
´S G. PALLARE
´S
1
, VALENTI
´N E. FERNA
´NDEZ-ELI
´AS
1
, JUAN F. ORTEGA
1
, GLORIA MUN
˜OZ
2
,
JESU
´S MUN
˜OZ-GUERRA
2
, and RICARDO MORA-RODRI
´GUEZ
1
1
Exercise Physiology Laboratory at Toledo, University of Castilla-La Mancha, Toledo, SPAIN; and
2
Spanish Anti-doping
Agency, Doping Control Laboratory in Madrid, SPAIN
ABSTRACT
PALLARE
´S, J. G., V. E. FERNA
´NDEZ-ELI
´AS, J. F. ORTEGA, G. MUN
˜OZ, J. MUN
˜OZ-GUERRA, and R. MORA-RODRI
´GUEZ.
Neuromuscular Responses to Incremental Caffeine Doses: Performance and Side Effects. Med. Sci. Sports Exerc., Vol. 45, No. 11,
pp. 2184–2192, 2013. Purpose: The purpose of this study was to determine the oral dose of caffeine needed to increase muscle force and
power output during all-out single multijoint movements. Methods: Thirteen resistance-trained men underwent a battery of muscle
strength and power tests in a randomized, double-blind, crossover design, under four different conditions: (a) placebo ingestion (PLAC)
or with caffeine ingestion at doses of (b) 3 mgIkg
j1
body weight (CAFF
3mg
), (c) 6 mgIkg
j1
(CAFF
6mg
), and (d) 9 mgIkg
j1
(CAFF
9mg
).
The muscle strength and power tests consisted in the measurement of bar displacement velocity and muscle power output during free-
weight full-squat (SQ) and bench press (BP) exercises against four incremental loads (25%, 50%, 75%, and 90% one-repetition maxi-
mum [1RM]). Cycling peak power output was measured using a 4-s inertial load test. Caffeine side effects were evaluated at the end of
each trial and 24 h later. Results: Mean propulsive velocity at light loads (25%–50% 1RM) increased significantly above PLAC for all
caffeine doses (5.4%–8.5%, P= 0.039–0.003). At the medium load (75% 1RM), CAFF
3mg
did not improve SQ or BP muscle power or
BP velocity. CAFF
9mg
was needed to enhance BP velocity and SQ power at the heaviest load (90% 1RM) and cycling peak power
output (6.8%–11.7%, P= 0.03–0.05). The CAFF
9mg
trial drastically increased the frequency of the adverse side effects (15%–62%).
Conclusions: The ergogenic dose of caffeine required to enhance neuromuscular performance during a single all-out contraction depends
on the magnitude of load used. A dose of 3 mgIkg
j1
is enough to improve high-velocity muscle actions against low loads, whereas a higher
caffeine dose (9 mgIkg
j1
) is necessary against high loads, despite the appearance of adverse side effects. Key Words: ERGOGENIC
AIDS, NEUROMUSCULAR EFFECTS, MUSCLE STRENGTH, MUSCLE POWER, LOAD–POWER RELATIONSHIP
The ergogenic effect of caffeine (1,3,7-trimetilxanthine)
on endurance performance is well recognized and has
been analyzed at length (7). In contrast, it is uncertain
if caffeine ingestion is ergogenic during short-term high-
intensity exercises. One plausible reason for the disagree-
ment between studies is the duration/intensity of the effort
undertaken. Controversial findings have been reported for
exercise performance durations 91 min to the point of
muscle failure (1,3,6,16,19,38), efforts lasting G1 min such
us the Wingate test and 20-m sprints (6,12,13,17), and single
maximal isometric (22,25,27,35), isokinetic (4,5,20), or
isoinertial contractions (3,6,29) lasting only a few seconds.
Differences in the muscle groups tested (6,14,37), doses of
caffeine ranging from 2 to 10 mgIkg
j1
, and disparity of
samples used that ranged from moderately active subjects to
resistance-trained athletes may have also contributed to the
observed differences between studies. In a recent meta-
analysis, Astorino and Roberson (2) reported caffeine ergo-
genic effects when testing muscle endurance (increased number
of repetitions to failure) but little evidence to sustain caffeine
ergogenic effects on maximum strength (one-repetition maxi-
mum [1RM]). The effects of caffeine on a single forceful
action should precede the study of several fatiguing repeti-
tions where metabolite accumulation may hinder the ergogenic
effect of caffeine. The present study attempts to address the
effects of caffeine on single all-out muscle contractions.
We have recently reported increases in maximum mus-
cle strength and power output with caffeine ingestion in
resistance-trained men (29), whereas others found similar
results in women (14). In contrast, other studies found
no effect when administering comparable caffeine doses
(3–6 mgIkg
j1
body weight) in similarly trained subjects
(3,38) or in collegiate football players (40). This uncertainty
is unfortunate because performance in many sports depends
on brief contractions that require a maximum rate of force
development. Even an ergogenic effect of caffeine on mus-
cle power as low as 5% (29) could influence performance in
these short actions. It thus seems relevant to clarify this issue
because world-class athletes of sports disciplines that require
high muscle strength and power (e.g., track cycling, Olym-
pic weightlifting, or volleyball) are among the ones with the
highest caffeine consumption (36).
Address for correspondence: Ricardo Mora-Rodrı
´guez, Ph.D., Universidad
de Castilla-La Mancha. Avda. Carlos III, s/n. 45071, Toledo, Spain; E-mail:
Ricardo.Mora@uclm.es.
Submitted for publication February 2013.
Accepted for publication May 2013.
0195-9131/13/4511-2184/0
MEDICINE & SCIENCE IN SPORTS & EXERCISE
Ò
Copyright Ó2013 by the American College of Sports Medicine
DOI: 10.1249/MSS.0b013e31829a6672
2184
APPLIED SCIENCES
Copyright © 2013 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited.
The minimal caffeine dose needed to enhance endurance
performance was first established in the classical study of
Graham and Spriet (15) (3 mgIkg
j1
) and later confirmed by
Kovacs et al. (24) (3.2 mgIkg
j1
) and other recent studies
(21) (2 mgIkg
j1
). During prolonged exercise, a delay in
central nervous system fatigue could be behind the ergo-
genic effect of caffeine on endurance performance. In con-
trast, caffeine effects on neuromuscular performance may
occur through a different mechanism involving improved
muscle excitation–contraction coupling (27,28). Because caf-
feine could be acting through a different mechanism of ac-
tion for endurance than for strength-power performance, the
dose of caffeine required to activate the mechanism could
also differ. Some studies suggest that a high caffeine dose
(5–7 mgIkg
j1
) is needed to elicit performance effects on
isokinetic strength (4,20). To our knowledge, no study has
addressed the dose of caffeine needed to improve strength
and power during isoinertial contractions of large muscle
groups. It is possible that the caffeine dose needed to obtain
an ergogenic effect may depend on the magnitude of the
resistance that the musculature has to overcome.
There is limited information regarding the side effects of
the caffeine doses usually ingested for improving sports
performance (3–9 mgIkg
j1
). A review suggests that caffeine
ingestion of doses higher than 9 mgIkg
j1
can lead to ad-
verse effects such as anxiety, restlessness, and headaches,
which could negatively affect endurance performance (2). In
addition, sleep deprivation due to caffeine ingestion could
impair athletic performance when the competition extends
over several consecutive days (31). We propose to study the
neuromuscular performance effects of caffeine by increas-
ing the dose while observing the side effects in the same
subjects. This analysis would identify the oral caffeine dose
that, while increasing neuromuscular performance, would
not result in undesirable side effects that may undermine
caffeine’s ergogenic potential.
Therefore, the purpose of this study was to find the oral
dose of caffeine that improves the voluntary contraction and
power of large muscle groups in resistance-trained athletes.
Different submaximal loads were used to investigate which
dose of caffeine enhances either slow-velocity high-
resistance contractions or high-velocity low-resistance con-
tractions. Second, we examined the side effects associated
with a complete range of caffeine doses and their possible
implications for the athletes’ performance. We hypothesized
that a high caffeine dose (96mgIkg
j1
) will be needed to
obtain an ergogenic effect on slow-velocity high-resistance
contractions, whereas lower caffeine doses (G6mgIkg
j1
)
will be ergogenic in high-velocity low-resistance contractions.
METHODS
Subjects. Thirteen highly resistance-trained men volun-
teered to participate in this study (age, 21.9 T2.9 yr; body mass,
76.5 T8.5 kg; height, 172.7 T5.4 cm; body fat, 12.4% T2.7%;
resistance training experience, 7.1 T3.5 yr). Their 1RM
strength for the free-weight full-squat (SQ) and bench press
(BP) exercises was 112.5 T12.6 and 121.0 T22.7 kg, re-
spectively, which accounted for 1.47 T0.16 and 1.58 T0.19
when normalized per kilogram of body mass. Most of the
subjects were resident in the sports performance center of
the Region of Murcia (Spain). The subjects were informed in
detail about the experimental procedures and the possible risks
and benefits of the project. The study complied with the
Declaration of Helsinki and was approved by the Bioethics
Commission of the University of Murcia. Before participa-
tion, written informed consent was obtained from each ath-
lete, and subjects were informed that they could resign from
participation at any time. All subjects were light caffeine
consumers (e70 mgId
j1
from caffeinated soda or lyophi-
lized coffee in milk).
Experimental design. A randomized, double-blind, cross-
over, placebo-controlled experimental design was used, with
all subjects serving as their own controls. Participants under-
went the same battery of neuromuscular and biochemical as-
sessments under four different conditions: (a) placebo trial
(PLAC) and three doses of caffeine ingestion: (b) 3mgIkg
j1
trial (CAFF
3mg
), (c) 6mgIkg
j1
trial (CAFF
6mg
), and (d)
9mgIkg
j1
trial (CAFF
9mg
). Trials were separated by 48 h to
avoid any possible fatigue and to allow caffeine washout (23).
All trials began at 8:00 a.m. to control the circadian rhythms
effects (29). Caffeine (Durvitan, Seid, Spain) was provided
in gelatin capsules to deliver doses of 3, 6, and 9 mgIkg
j1
body mass, respectively. The capsules were ingested 60 min
before the trial to allow peak blood caffeine concentration
(10) (Fig. 1). In the trial without caffeine ingestion (PLAC
trial), subjects ingested placebo capsules filled with the same
amount of dextrose to avoid identification. The amount of
additional energy provided by the dextrose (È2 kcal) was
deemed negligible.
Familiarization. All subjects had previously partici-
pated in experiments involving all the muscle strength and
power tests performed in this study. Nevertheless, partici-
pants underwent seven familiarization sessions before the
start of the experimental trials to avoid the bias of progres-
sive learning. The last familiarization session, performed in
the morning (8:00 a.m.) of the third day before the beginning
of the study, included the determination of the individual
load (kg) corresponding to 25%, 50%, 75%, and 90% of
1RM in the BP and SQ exercises for each subject. To carry
out that assessment, the initial load was set at 20 kg for
all subjects and was increased in 10-kg increments until
the attained mean propulsive velocity (MPV) was less than
0.5 mIs
j1
in the BP or less than 0.8 mIs
j1
in the SQ because
those velocities indicate proximity to 1RM (32). Thereafter,
the load was adjusted with smaller increments so that 1RM
could be precisely determined. The heaviest load that each
subject could properly lift while completing the full range of
motion was considered to be his 1RM.
Experimental protocol. The day before and during the
7 d that the experiment lasted, the subjects lived at the sports
performance center where they slept and ate all meals. They
CAFFEINE DOSE AND NEUROMUSCULAR RESPONSE Medicine & Science in Sports & Exercise
d
2185
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all consumed a diet of 2800–3000 kcalId
j1
, composed of
55% energy intake from carbohydrates, 25% from fat, and
20% from protein, evenly distributed across three meals
each day (breakfast at 7:00 a.m., lunch at 13:30 p.m., and
dinner at 20:00 p.m.). Subjects refrained from physical ac-
tivity other than that required by the experimental trials and
withdrew from alcohol, tobacco, and any kind of caffeine
intake 10 d before testing and while the experiment lasted.
The day before the onset of the experiment, height was
measured in the morning to the nearest 0.5 cm during a
maximal inhalation using a wall-mounted stadiometer (Seca
202; Seca Ltd., Hamburg, Germany).
In every trial, upon arrival to the testing facility at
6:30 a.m. in a fasted state (PRE), a urine sample (15 mL)
was obtained. Urine specimens were measured in duplicate
for urine-specific gravity (U
SG
; Uricon-NE, Atago, Japan),
and the rest of the sample was immediately frozen at j20-C
for future analysis. Then, the subject’s body weight was
determined and body water estimated using a four-contact
electrode body composition bioimpedance analyzer (Tanita
TBF-300A; Tanita Corp., Tokyo, Japan) to obtain a percent-
age of body fat and fat-free mass. Following this, tympanic
temperature (Thermoscan, Braun, Germany) was measured
in triplicate after the removal of earwax when needed.
Next, a 5-mL blood sample was withdrawn from an ante-
cubital vein without stasis. A small portion of the whole blood
wasusedtodeterminehematocrit by triplicate using no-
heparinized capillary tubes (70 KL; Hirschmann Laborgerate,
Germany) and a microcentrifuge (Biocen, Arlesa, Spain).
The serum and plasma obtained after centrifugation (3000g)
was immediately stored at j70-C. Then, subjects ingested
the capsules containing their individualized-randomized caf-
feine dose (3, 6, or 9 mgIkg
j1
) or placebo with 330 mL of a
fruit milkshake (168 kcal) and a pastry (456 kcal) that served
as a standardized breakfast (total of 624 kcal and 68 g of
carbohydrate).
After a standardized warm-up that consisted of 10 min
of jogging at 10 kmIh
j1
and 10 min of static stretches and
joint mobilization exercises, the subjects entered the labo-
ratory to start the neuromuscular test battery assessments
under a paced schedule (see Fig. 1). These tests consisted of
the measurement of bar displacement velocity and muscle
power output against four incremental loads (25%, 50%,
75%, and 90% of 1RM) for upper and lower body muscu-
lature (BP and SQ). Those step measures allowed a contin-
uous representation of the load–velocity and load–power
curves to study the interaction between load and caffeine
dose on neuromuscular performance. Cycling peak power
output (PPO) was assessed next using a nonfatiguing iner-
tial load test of 4-s duration. Subjects remained blinded to
the results during the whole experiment. Instructions before
lifting were standardized and always delivered by the same
experimenter.
Upon completion of the test battery (È60 min from the
beginning of the neuromuscular assessments), a second
urine and blood sample were collected (POST). Then, sub-
jects filled out a questionnaire (QUEST + 0 h) aimed to
address whether side effects of caffeine were present during
the trial. Subjects were then discharged and reminded about
their schedule for the next trial. Blood and urine caffeine
concentration was evaluated at the beginning (PRE) and
immediately at the end (POST) of each trial. U
SG
and blood
hematocrit were also determined PRE and POST each trial.
Load–velocity and load–power relationships. We
used a graded loading test in a Smith machine (Multipower
Fitness Line, Peroga, Spain) with a linear encoder and its
associated software (T-Force System; Ergotech, Murcia, Spain;
0.25% accuracy) attached to the bar by a light retractable
metal cable. There were two Smith machines, each one
dedicated to a given exercise (SQ or BP). Both encoders
were cross validated before the test with agreement of
r= 0.999. A detailed description of the validity and reli-
ability data of the dynamic measurement system (ICC = 1.00,
CV = 0.57%) has recently been reported (32). At the indi-
vidually determined 25%, 50%, 75%, and 90% of 1RM
(see Familiarization section), changes in bar displacement
velocity and power output were measured after the inges-
tion of different caffeine doses. MPV and mean propulsive
power (MPP) were calculated as the average velocity and
power output values, respectively, measured only during the
propulsive phase, defined as that portion of the concentric
action during which the acceleration is greater than accel-
eration because of gravity (33). In each trial, three attempts
were executed for light (25% RM), two for medium (50%
RM), and only one for the heaviest (75% and 90% RM)
loads interspersed with 5 min of passive rests. Only the best
FIGURE 1—Experimental protocol.
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repetition at each load, according to the criteria of fastest
MPV, was considered for subsequent analysis.
The individual range of movement during the BP and SQ
exercises was carefully replicated in each trial with the help
of two telescopic bar holders with a precision of T1.0 cm.
In the BP, the bar holders were positioned to allow the bar
to descend to 1 cm above each subject’s chest. In the SQ, the
bar holders were set at each subject’s lowest squat depth
defined as that position in which the back of the thighs and
upper calves made contact with each other. Subjects were
instructed to perform the eccentric phase of both exercises
in a slow and controlled manner, to pause for 2 s at the bar
holders, momentarily releasing the weight, and thereafter to
perform a purely concentric action pushing back up at max-
imal intended velocity. The momentary pause imposed be-
tween the eccentric and the concentric actions was designed
to minimize the contribution of the stretch-shortening cycle
(i.e., rebound effect) and to allow for more reliable and
consistent measurements. Pilot data collected during the
previous familiarization revealed significant reductions in
the intrasubject coefficient of variation when using the de-
scribed technique compared with a nonstop technique in-
volving the stretch-shortening cycle (i.e., 3.5% vs 2.4% for
BP and 3.7% vs 2.7% for SQ exercise, both PG0.05).
Cycling peak power test. Cycling PPO was measured
using the previously described isoinertial load test (26). In
brief, we measured the power needed to overcome the in-
ertial load of a heavy (21.5 kg) cycle-ergometer flywheel
(Monark-818, Varberg, Sweden). This cycling PPO assess-
ment lasts only 4 s; however, a complete power–velocity
spectrum curve is generated using an absolute encoder (ASM
2000 ppr; Unterhaching, Germany; 1000 Hz) connected to the
cycle ergometer flywheel. Subjects sat on the cycle ergometer
after the handlebars and saddle had been adjusted to fit their
individual’s body dimensions. After a 3-min warm-up (100 W
at 90 rpm interspersed with two short (2–3 s) bouts of maximal
acceleration), subjects performed two maximal sprints inter-
spersed by 180 s of active recovery (50 W). The test started
from a complete stop with the pedal of the dominant leg
placed at 45-from the vertical. The test–retest intraclass cor-
relation coefficient was 0.85 (0.60–0.95), and the coefficient
of variation was 3.9% T1.3%. The average value of the two
PPO sprints was recorded for data analysis.
Urine and plasma analysis. Blood samples (5 mL)
were mixed with ethylenediaminetetraacetic acid in plastic
tubes and plasma immediately separated by centrifugation
(MPW-350R; MedInstruments, Poland). The plasma samples
were stored at j80-C for future analysis. At a later date, urine
and plasma samples were analyzed for caffeine concentra-
tions and related metabolites using an Agilent Technologies
HPLC 1200 system (Santa Clara, CA) coupled to a triple
quadrupole/ion trap mass spectrometer (MS; API 4000, Q TRAP,
AB SCIEX, Framingham, MA US). Methylxanthine internal
standards were purchased from Cerilliant (Round Rock, TX).
Aliquots of urine sample (100 KL) were filtered (VWR,
Barcelona, Spain) and transferred into a liquid chromato-
graphy vial containing 900 KL of mobile phase (aqueous
solution of 0.1% acetic acid). Subsequently, 20 KLofinternal
standard working solution (caffeine
13
C
3
5KgImL
j1
)was
added and mixed. Ten microliters of the sample was then
directly applied to the HPLC-MS system. For blood, 20 KL
of the internal standard working solution was added to
the aliquots of plasma sample (100 KL). The sample was
vortex mixed for 10 s, then 20 KL of 20% perchloric acid
was added, and the sample was vortex mixed for 10 s and
centrifuged at 3500 rpm for 10 min. One hundred microliters
of the supernatant was transferred into a liquid chromatogra-
phy vial containing 900 KL of mobile phase and mixed. Then
the sample was filtered through 0.2 Km of cellulose acetate
membrane, 25-mm syringe filters, and 10 KL was then di-
rectly applied to the HPLC-MS system. To calibrate the
system, aqueous solutions of caffeine (ranging from 0.25 to
12 KgImL
j1
) were used for each batch of samples. The lower
limit for the accurate quantization of these methylxanthines
was 0.25 KgImL
j1
.
Side effects evaluation. Immediately after each neu-
romuscular test battery (QUEST + 0 h) and 24 h later
(QUEST + 24 h), participants answered a questionnaire. The
QUEST + 0 h was designed to evaluate the physical fatigue,
the perceived performance, and the side effects (e.g., urine
output, gastrointestinal problems, tachycardia, or headache)
felt by the participants during the neuromuscular test battery.
QUEST + 24 h was designed to evaluate physical fatigue
and side effects (e.g., sleep quality, gastrointestinal prob-
lems, tachycardia, muscle soreness, or headache) perceived
by participants during the 24 h after the caffeine dose was
ingested. These surveys included eight items on a yes/no
scale and were based on previous publications about side
effects derived from the ingestion of caffeine (8,11).
Statistical analysis. The Shapiro–Wilk test was used
to assess normal distribution of data. Pretesting conditions,
the cycling isoinertial load power test and the caffeine levels
data were analyzed using one-way ANOVA for repeated
measures (doses of caffeine). The load–velocity and load–
power relationships were analyzed using two-way (caffeine
dose load) ANOVA for repeated measures. The Greenhouse–
Geisser adjustment for sphericity was calculated. After a sig-
nificant F-test, differences among means were identified
using pairwise comparisons with Bonferroni’s adjustment.
The significance level was set at Pe0.05. Cohen’s formula
for effect size (ES) was used, and the results were based on
the following criteria: 90.70 large effect, 0.30–0.69 moderate
effect, and e0.30 small effect (9). Reported side effects in
the questionnaires were not normally distributed, and a non-
parametric statistical technique was used.
RESULTS
Pretesting conditions, hydration status. Before the
four experimental trials (PRE), body mass (range between
76.4 T8.5 and 76.9 T8.2 kg) and body bioimpedance (range
between 462 T46 and 475 T54 6) were not different between
CAFFEINE DOSE AND NEUROMUSCULAR RESPONSE Medicine & Science in Sports & Exercise
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Copyright © 2013 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited.
trials (PLAC, CAFF
3mg
,CAFF
6mg
, and CAFF
9mg
). No sig-
nificant differences were detected between treatments in
PRE testing conditions for tympanic temperature, blood he-
matocrit, or urine U
SG
. POST tympanic temperature values
in all trials (PLAC, CAFF
3mg
, CAFF
6mg
, and CAFF
9mg
)
were significantly elevated (range of increase = 1.5%–2.2%,
P= 0.000–0.041, ES = 1.10–1.70) when compared with
their respective PRE value. No significant differences were
detected for hematocrit or urine U
SG
values between PRE
and POST conditions at any dose, except in the CAFF
9mg
trial where hematocrit was significantly higher (from 45.4% T
3.7% to 47.0% T3.9%, P= 0.031, ES = 0.42), and urine U
SG
was significantly lower (from 1.024 T0.005 to 1.016 T0.007,
P= 0.003, ES = 1.40) in the POST testing conditions.
Caffeine side effects. Immediately after the PLAC
trial, subjects reported a very low frequency of side effects
(0%–8%; QUEST + 0 h). The CAFF
3mg
and the CAFF
6mg
treatments produced very similar side effects, with a limited
increase in the sensations of tachycardia and heart palpita-
tions, self-reported urine output, and gastrointestinal prob-
lems (8% of the subjects) compared with the PLAC trial. On
the other hand, the subject’s perception of performance and
vigor increased five to seven times above PLAC during the
CAFF
3mg
and CAFF
6mg
trials (38% and 54% of the sub-
jects, respectively). Finally, the CAFF
9mg
trial produced a
drastic increase in the reported frequency of side effects
(Table 1). It is particularly relevant that 62% and 31% of
participants reported an increase in the estimates of urine
output and gastrointestinal problems, respectively. The per-
ception of performance and vigor or activeness also rose in
62% and 54% of the participants, respectively (Table 1).
The following morning of each experimental trial
(QUEST + 24 h), very few participants (8%) reported that
PLAC treatment produced residual side effects such as
muscle soreness, increase in the estimates of urine output,
and gastrointestinal problems. The CAFF
3mg
trial produced
very similar side effects to PLAC, with an additional 8% of
participants reporting a headache. The CAFF
6mg
trial tended
to increase the frequency of muscle soreness and head-
aches and the estimates of urine output in comparison with
the PLAC and CAFF
3mg
treatments, although still with a
frequency lower than 31% of the subjects. In addition,
CAFF
6mg
produced symptoms of increased vigor and sleep
problems, although with a very low incidence (8%). Finally,
CAFF
9mg
increased the frequency of all adverse side effects,
with a frequency of appearance from 23% to 54%. Of note,
23% of participants reported tachycardia and anxiety or
nervousness, 38% with gastrointestinal problems, and 54%
with insomnia or sleep disturbances (Table 1).
Load–velocity and load–power relationship. MPV
attained against the two lower loads (25% and 50% 1RM)
in the BP and SQ exercises significantly increased with all
caffeine doses (CAFF
3mg
,CAFF
6mg
and CAFF
9mg
) com-
pared with the placebo treatment (PLAC) (range of in-
crease = 5.4%–8.5%, P= 0.039–0.000, ES = 0.76–1.28;
Fig. 2). Similarly, MPV at 75% 1RM was significantly
increased in all caffeine trials in the BP and SQ exer-
cises compared with the placebo treatment (PLAC) (range
TABLE 1. Side effects reported by participants immediately after the conclusion of each neuromuscular test battery (QUEST + 0 h) and 24 h later (QUEST + 24 h).
PLAC CAFF
3mg
CAFF
6mg
CAFF
9mg
+0 h +24 h +0 h +24 h +0 h +24 h +0 h +24 h
Muscle soreness 15 8 8 8 8 31 15 38
Increased urine output 8 8 15 8 15236254
Tachycardia and heart palpitations 8 0 15 0 15 0 23 23
Anxiety or nervousness 80 8015 03123
Headache 80 08 8231538
Gastrointestinal problems 08 88 8 83138
Insomnia —0—0— 854
Increased vigor/activeness 8 0 38 0 46 8 54 23
Perception of performance improvement 8—54—54—62—
Data are presented as the percentage of prevalence.
FIGURE 2—Dose–response effects of caffeine ingestion on load–
vel ocity relationship forbench press (A) and full squat (B)exercises. Data
are means TSD. *Significant differences (Pe0.05) compared with the
PLAC trial within each load.
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Copyright © 2013 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited.
of increase = 6.3%–8.9%, P= 0.046–0.014, ES = 0.91–1.21;
Fig. 2). The only exception was for the CAFF
3mg
trial in the
BP exercise (P= 0.15). Finally, MPV at the heaviest load
(90% 1RM) was significantly enhanced with the CAFF
9mg
compared with placebo in both exercises (BP: 13.1%,
P= 0.031, ES = 0.74; SQ: 10.4%, P= 0.046, ES = 1.03).
During SQ at 90% 1RM, a caffeine dose of CAFF
6mg
was also enough to increase MPV above PLAC (8.3%,
P= 0.029, ES = 0.90; Fig. 2B).
MPP at the two light loads (25% and 50% 1RM) in the
BP and SQ exercises was significantly increased with all
caffeine doses (CAFF
3mg
, CAFF
6mg
and CAFF
9mg
) com-
pared with PLAC (range of increase = 8.1%–12.0%,
P= 0.022–0.000, ES = 0.36–0.68), except for the CAFF
3mg
treatment in the SQ exercise (P= 0.18–0.09). At 75% 1RM,
MPP in the BP and SQ was also significantly increased
in the CAFF
6mg
and CAFF
9mg
trials compared with PLAC
(range of increase = 8.3%–10.2%, P= 0.037–0.010,
ES = 0.36–0.48). Finally, MPP at 90% 1RM was signifi-
cantly enhanced in the CAFF
9mg
trial for BP and SQ
(11.7%–15.0%, P= 0.031–0.014, ES = 0.47–0.92) and with
the CAFF
6mg
dose for the BP exercise (11.4%, P= 0.021,
ES = 0.71) compared with PLAC (Fig. 3A and B). The
peak in mean power in the BP exercise occurred at 25%
1RM, independently of the caffeine dose ingested (range =
501–562 W), and was significant lower at 75% and 90%
1RM loads (range 267–423 W, PG0.001; Fig. 3A). The
peak in mean power for SQ occurred at 75% 1RM in all
trials (range = 525–579 W) and was significantly lower
at 25% 1RM (range 356–400 W, PG0.001; Fig. 3B).
Cycling PPO test. No significant differences were de-
tected in cycling PPO in absolute (W) or normalized per
kilogram of FFM (WIkg
j1
) values between PLAC, CAFF
3mg
,
and CAFF
6mg
trials. However, a significantly 7.0% higher
PPO was detected in the CAFF
9mg
trial (1506 T225 W) com-
pared with PLAC (1408 T189 W, P= 0.040, ES = 0.47).
Likewise, a significantly 6.9% higher PPO/FFM was de-
tected in the CAFF
9mg
trial (22.7 T1.8 WIkg
j1
) com-
pared with the PLAC trial (21.2 T1.4 WIkg
j1
,P=0.036,
ES = 0.88; Fig. 4).
Urine and blood analysis. Upon arrival to the labo-
ratory (PRE), plasma (G0.13 T0.08 KgImL
j1
) and urine
(G0.12 T0.15 KgImL
j1
) caffeine concentrations were neg-
ligible in all subjects, confirming the complete caffeine
washout before trials. At the end of the test battery (i.e.,
POST: 2 h after the caffeine or placebo ingestion), urine
and plasma caffeine concentrations in all caffeine trials
(CAFF
3mg
, CAFF
6mg
, and CAFF
9mg
) were significantly
higher (PG0.05) than their respective basal values. The
ingestion of the graded caffeine doses produced a signifi-
cant parallel increase in plasma and urine caffeine concen-
trations at their respective POST values (PG0.05; Fig. 5).
DISCUSSION
The main finding of this study is that caffeine signifi-
cantly improves movement velocity under all loading con-
ditions (from 25% to 90% 1RM) in both the upper (BP)
and the lower body (SQ) musculature. The higher the load,
and thus the longer time available to apply force, the higher
the caffeine dose needed to achieve an ergogenic effect
FIGURE 3—Dose–response effects of caffeine ingestion on load–power
relationship for bench press (A) and full squat (B) exercises. Data are
means TSD. *Significant difference (Pe0.05) between CAFF
3mg
and
PLAC. Significant difference (Pe0.05) between CAFF
6mg
and PLAC.
Significant difference (Pe0.05) between CAFF
9mg
and PLAC.
a
Significantly lower (Pe0.05) than the peak power (25% 1RM for BP
and 75% for full squat) for each exercise.
FIGURE 4—Dose–response effects of caffeine ingestion on cycling
PPO using a 4-s inertial load test in absolute and fat-free mass nor-
malized values. Data are means TSD. *Significantly different (Pe0.05)
than PLAC.
CAFFEINE DOSE AND NEUROMUSCULAR RESPONSE Medicine & Science in Sports & Exercise
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(see Fig. 3). We have previously reported a È5% MPV
improvement in BP and SQ exercises after ingestion of
3mgIkg
j1
of caffeine against loads of 75% 1RM (29). In the
present study, we observe improvements between 5.2% and
13.1%, depending on the dose of caffeine ingested and
the magnitude of the resistance to overcome. Interestingly,
the ergogenic effect of caffeine against the lighter loads
(25%–50% of 1RM) was maximal with a low dose of caf-
feine (3 mgIkg
j1
). In contrast, higher caffeine doses were
required to improve performance against higher loads
(6 mgIkg
j1
for 75% 1RM and 9 mgIkg
j1
for 90% 1RM
load). This seems to suggest that the dose of caffeine re-
commended will depend on the resistance that athletes have
to overcome. As we will discuss latter, administering the
minimal ergogenic dose would be recommended to avoid
undesirable adverse side effects.
As observed in Figure 2, caffeine increased movement
velocity in 20 of the 24 caffeine ingestion trials (83% ef-
fectiveness). This consistency on the ergogenic effects of
caffeine has no comparison in the literature that examines
caffeine effects on resistance exercise. Some studies found
no effect of caffeine on maximum strength measured as
1RM (1,3,38) or the number of repetitions to failure against
a submaximal load (1,3,6,16,19,38–40). However, our data
are not directly comparable with those studies addressing the
effect of caffeine ingestion using the 1RM test. The repro-
ducibility (CV = 2.9%–5.3% [34]) and accuracy (usually
2.5–5.0 kg at each side of the bar) for typical 1RM tests is
lower than those reported using a linear velocity transducer
(CV = 0.57%, accuracy = 0.25%, 1000 Hz [32]). These
improvements in the quality of the measure allow us to de-
tect small but significant effects of caffeine on performance
(29). Others have reported an increased peak torque after
caffeine ingestion using isokinetic or isometric devices.
Astorino et al. (4) found that a 5-mgIkg
j1
dose of caffeine
improved isometric power whereas a lower 2 mgIkg
j1
had
no effect. Jacobson et al. (20) reported that 7 mgIkg
j1
caf-
feine ingestion improved peak isometric torque at several
angular velocities, findings that have been recently con-
firmed by Bazzucchi et al. (5). Our findings using isoinertial
loads and an accurate measure of bar velocity are compara-
ble with those using isokinetic tests in that caffeine is ergogenic
during single muscle actions against several external resistances.
We found that a high dose of caffeine (9 mgIkg
j1
) was
needed to improve peak power in our highly reproducible
(CV = 3.9%) and sensible (sampling frequency 1000 Hz)
inertial load cycling test (Fig. 4). In this test, subjects have
to overcome the inertial load of a heavy (21.5 kg) cycle-
ergometer flywheel. Thus, during the initial pedal strokes of
the 4-s test, the leg musculature is required to develop a high
percentage of their MVC (26). In agreement with the SQ
data (Fig. 3B), only the highest dose of caffeine was ergo-
genic against the high inertial load. Our data are similar to
those of Glaister et al. (13) in that we did not find an effect
of caffeine on cycling sprint peak power with doses of 3
and 6 mgIkg
j1
. However, we found an ergogenic effect
with 9 mgIkg
j1
, whereas they did not with doses of 8 or
10 mgIkg
j1
. However, Glaister et al. reported a tendency for
a reduction in the time to peak power at the highest caffeine
dose. Our tests differed in the length of the sprint; ours being
less than half of the duration compared with that of Glaister
et al. (i.e., 4 vs 10 s). It seems that the longer the duration of
the sprint, the less likelihood of finding an effect of caffeine
ingestion. In fact, studies using the regular 30-s Wingate test
to investigate the effects of caffeine are inconclusive with
either positive (39) or negative (6,17,38) findings. In sum-
mary, our results using repeated muscle contractions (4 s
cycling sprint against an inertial load; Fig. 4) confirm the
results observed during single muscle actions (Fig. 3) in that a
high dose of caffeine is needed when the resistance to over-
come is high.
The results of the present study show a greater caffeine
ergogenic effect on the lower compared with the upper
body musculature, particularly at the higher resistances and
caffeine doses (Fig. 2). These results are consistent with
previous findings by Astorino et al. (1), who found an ergo-
genic effect of caffeine ingestion on repetitions to failure
for leg press, but not for BP exercise. In a recent meta-
analysis, Warren et al. (37) found more consistent effects of
caffeine ingestion on improving 1RM knee extension than
that in other muscle groups. In contrast, other researchers
found enhanced 1RM strength (6) and number of repeti-
tions to failure (39) in the BP but not in the leg press
exercise, whereas others found no differences between
muscle groups (3,19). These discrepancies could be due to
(i) the order of the testing, because 1RM or repetitions to
failure tests induce central fatigue that can influence the
secondmusclegrouptestedassuggestedbyAstorinoetal.
(3), and (ii) the relatively low reliability of the muscle en-
durance tests. We have attempted to reduce the measure-
ment variability by testing only single explosive actions with
the velocity transducer and with our careful testing protocol.
Our results allow us to suggest that caffeine has a larger ergo-
genic effect during lower body muscle contractions. Additional
research is needed to identify the underlying mechanism re-
sponsible for these differences between upper and lower body
FIGURE 5—Dose–response effects of caffeine ingestion on urine and
plasma caffeine concentrations at PRE and POST time points. Data are
means TSD. *Significantly different (Pe0.05) when compared with
their respective POST value. Significantly different (Pe0.05) when
compared with their previous caffeine dose trial.
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Copyright © 2013 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited.
musculature. Warren et al. (37) argued that the muscle activa-
tion level during MVC may be lower for the knee extensors
than for other smaller muscle groups. In these smaller groups,
muscle activation without caffeine is already near 100%, and
thus there is minimal room for caffeine to improve contraction
force. This seems to us a very plausible explanation.
Although no subject reached the 2004 urinary caffeine
threshold for doping (12 KgImL
j1
; Fig. 5), some of the
doses produced side effects that remained 24 h after the trial.
One of the findings of the present study was that the pre-
sence of negative side effects increased markedly with the
9-mgIkg
j1
caffeine dose (Table 1). To our knowledge, these
results are novel in the literature for a controlled, double-
blind, crossover design where three incremental doses of
caffeine are evaluated. In a descriptive cross-sectional study,
Desbrow and Leveritt (11) associated habitual caffeine use
by Ironman athletes with side effects and found very minor
and infrequent adverse caffeine-related symptoms during
this long distance endurance event. Their retrospective data
did not allow them to analyze the dose–side effects rela-
tionship. In the present study, we found gastrointestinal
problems, headaches, and insomnia appearing with doses at
or higher than 6 mgIkg
j1
(Table 1). In sport events lasting
longer than half a day (morning or afternoon), these side
effects generated by early caffeine ingestion could reduce
cognitive and physical performance. The side effects data,
together with the muscle strength and mechanical power
output results, allow us to suggest that only in events where
the sport success depends on force application against high
loads, like Olympic weightlifting or the start and the first
1–5 cycles or strokes in sprints, would it be advisable to
ingest caffeine doses higher than 6 mgIkg
j1
.
Few studies have reported a wide range of load–power
data in these basic resistance training exercises (BP, SQ).
Figure 3 suggests that the shape of the load–power curve
is not affected by caffeine ingestion. Furthermore, our data
coincide with previous reports (18,33) in showing that
muscle power output is very different in BP (25% 1RM) and
SQ (75% 1RM) exercises, probably due to the biomechanics
of the primary muscles recruited in each movement. Finally,
no significant differences were observed in the power output
developed against 25%–50% 1RM loads in BP, or against
50%–90% 1RM loads in SQ (Fig. 3). Attending to the load–
power data (Fig. 3), it could be suggested that there is not
one but a range of loads that maximize muscle power output
(low loads for BP and moderate loads for SQ), and caffeine
ingestion does improve power at all loads. In agreement with
recent reports (33), these results make us wonder whether
perhaps excessive attention has been paid to the question of
identifying a single load for maximizing power output.
While delaying central nerve fatigue could be one of
the mechanisms by which caffeine could improve repeated
sprint ability, it is less likely that it could improve single
muscle actions or very short sprint performance (i.e., 4 s
long) where fatigue is not limiting. In support for a local
muscle mechanism, caffeine ingestion has been reported to
increase the electrically evoked force of small (finger ad-
ductor [25]), medium (peroneus [35]), and large (quadriceps
[29]) muscle mass when stimulated at a low frequency
(20 Hz). In addition, several studies have failed to show
increased motor unit activation with caffeine using electro-
stimulation superimposed into a maximal voluntary con-
traction (27,35). In contrast, others have found increased
maximal activation using the twitch interpolation technique
(22,30). As the motor unit recruitment and firing rate are
likely larger during resistance than during endurance type
activities, it could be hypothesized that caffeine could fur-
ther benefit resistance exercise if a local effect is predomi-
nant. However, caffeine ingestion has not been shown to
increase motor unit firing rates in nonfatigued muscle (22,30).
Again, a bout of maximal contraction could be limited by
the capacity to voluntarily activate motor units, which seems
to be improved by caffeine ingestion (22). Thus, it is unclear
by which mechanism (local or central) caffeine ingestion is
improving force and power during single muscle actions.
In conclusion, in this study, we systematically raised caf-
feine dose while varying the load imposed to large muscle
groups located in the upper and lower body (BP and SQ). The
velocity of movement against those loads was improved
in 83% of the trials with caffeine (4.3%–13.1%) and thus
muscle power output. Importantly, as resistance increased
toward 1RM, a higher dose of caffeine was needed to in-
crease MPV (Fig. 2) and power (Fig. 3). Although no sub-
ject reached the 2004 urinary caffeine threshold for doping,
the increase in dosage produced side effects like gastroin-
testinal problems, anxiety, and headaches that remained 24 h
after the trial (Table 1). The practical application for sport
nutrition and performance is that muscle contractions against
heavy loads (75%–90% 1RM) also require a high caffeine
dose (9 mgIkg
j1
) to obtain an ergogenic effect. However,
explosive, high-velocity low-resistance actions require a much
lower caffeine dose (3 mgIkg
j1
), thus avoiding the undesir-
able side effects.
The authors thank the collaboration of Jose´ Marı´a Lo´ pez Gullo´n,
Ricardo Mora´ n Navarro, Alvaro Lo´ pez Samanes, and Luis Sa´ nchez
Medina from the High-Performance Sports Center Infanta Cristina,
University of Murcia, University of Castilla-La Mancha and Research
and Sports Medicine Centre from the Government of Navarre, re-
spectively. They also acknowledge the commitment and dedication
to the testing of each of the 13 high-performance athletes that par-
ticipated in this investigation.
No funding was received for this work. The authors report no
conflicts of interest.
The results of the present study do not constitute endorsement
by the American College of Sports Medicine.
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... Concretely, doses equivalent to 3-6 mg/kg are commonly recommended to enhance exercise and sports performance [13,14]. Interestingly, literature on the potential dose-response effect of caffeine on exercise performance indicates that oral caffeine intake produces an ergogenic benefit of similar magnitude within the dose range of 3-9 mg/kg [15][16][17][18]. Doses below 3 mg/kg of caffeine habitually do not produce ergogenic benefits [19,20], although this is now always the case in some exercise contexts [21]. ...
... However, the ergogenic benefit of caffeine, measured as the time to exhaustion during running at 85% of VO 2max , was of similar magnitude with 3, 6 and 9 mg/kg of caffeine. This investigation established the starting point of the lack of dose-response, in terms of ergogenic effect, of oral caffeine intake and contributed to the current knowledge that considers caffeine as a substance that produces comparable benefits in the dose range of 3-9 mg/kg, at least for individuals with low habituation to caffeine [15,17,18]. Graham and Spriet's investigation [15] also contributed to understand the mechanism associated to caffeine's ergogenicity as the metabolic responses seemed to uncouple from the performance benefits of the substance. ...
Article
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Purpose The effect of caffeine to enhance fat utilisation as fuel for submaximal aerobic exercise is well established. However, it is unknown whether this effect is dose dependent. The aim of this study was to investigate the effect of 3 and 6 mg of caffeine per kg of body mass (mg/kg) on whole-body substrate oxidation during an incremental cycling exercise test. Methods In a double-blind, randomised, and counterbalanced experiment, 18 recreationally active males (maximal oxygen uptake [VO2max] = 56.7 ± 8.2 mL/kg/min) performed three experimental trials after ingesting either 3 mg/kg of caffeine, 6 mg/kg of caffeine or a placebo (cellulose). The trials consisted of an incremental exercise test on a cycle ergometer with 3-min stages at workloads from 30 to 80% of VO2max. Energy expenditure, fat oxidation rate, and carbohydrate oxidation rate were continuously measured by indirect calorimetry. Results During exercise, there was significant effect of substance (F = 7.969; P = 0.004) on fat oxidation rate. In comparison to the placebo, the rate of fat oxidation was higher with 3 mg/kg of caffeine at 30, 40, 50 and 70% of VO2max [all P < 0.050, effect sizes (ES) from 0.38 to 0.50] and with 6 mg/kg of caffeine at 30, 40, 50, 60 and 70% of VO2max (all P < 0.050, ES from 0.28 to 0.76). Both 3 mg/kg (0.40 ± 0.21 g/min, P = 0.021, ES = 0.57) and 6 mg/kg of caffeine (0.40 ± 0.17 g/min P = 0.001, ES = 0.60) increased the maximal rate of fat oxidation during exercise over the placebo (0.31 ± 0.15 g/min). None of the caffeine doses produced any significant effect on energy expenditure or heart rate during exercise, while both caffeine doses reduced perceived fatigue at 80% of VO2max (all P < 0.050, ES from 0.71 to 1.48). Conclusion The effect of caffeine to enhance fat oxidation during submaximal aerobic exercise is of similar magnitude with 3 and 6 mg of caffeine per kg of body mass. Thus, a dose of 3 mg of caffeine per kg of body mass would be sufficient to enhance fat utilisation as fuel during submaximal exercise.
... As a multifactorial game, basketball includes shooting and passing accuracy as an integral, crucial, and most frequent technical part of the activity [5,6]. During a basketball match, players perform over 50 jumps [7], 48.7% of all basketball activities include combination of jumping and shooting movements, and 28.5% imply repeated sprint ability [8]. Additionally, a distance of 4000 to 5000 m is covered within 40 min [9]. ...
... Some authors [24] do not recommend the use of caffeine in Nutrients 2022, 14,1930 7 of 10 team sports with the ball, in which technical and tactical elements are a key factor [5,6]. Namely, the use of caffeine leads to insomnia, increased nervousness, and tremor [48,49], which can negatively affect the mentioned parameters. However, although the use of caffeine initiated increased insomnia [30] after the experimental treatment, caffeine also increased the number of rebounds, assists, performance index, and total body impacts [30] by increasing awareness and alertness during testing basketball players. ...
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Caffeine supplementation has become increasingly popular among athletes. The benefits of caffeine include delaying the negative effects of fatigue, maintaining a high level of physical and mental performance, and improving certain abilities necessary for sport success. Given the complex nature of basketball, caffeine could be a legal, ergogenic stimulant substance, which will positively affect overall basketball performance. The purpose of this systematic review was to summarize evidence for the effect of acute caffeine ingestion on variables related to the basketball performance. Web of Science, PubMed, Scopus and ProQuest, MEDLINE, and ERIC databases were searched up to February 2021. Studies that measured the acute effect of caffeine on basketball performance were included and analyzed. Eight studies published between 2000 and 2021 were included in the analysis. Pre-exercise caffeine intake increased vertical jump height, running time at 10 and 20 m without the ball, overall basketball performance (number of body impacts, number of free throws, rebounds, and assists) during simulated games, and reduced the time required to perform a basketball-specific agility test. Equivocal results between caffeine and placebo groups were found for aerobic capacity, free throw and three-point accuracy, and dribbling speed. Pre-exercise caffeine ingestion did not affect RPE, but insomnia and urinary excretion were increased. The pre-exercise ingestion of 3 and 6 mg/kg caffeine was found to be effective in increasing several physical performance variables in basketball players during sport-specific testing and simulated matches. However, considering the intermittent nature and complexity of basketball, and individual differences between players, future studies are needed.
... Although various doses of CAF, ranging from 3 to 13 mg/kg/body mass, have been utilized in the literature [12,14,15], as regards the power output, most often low (3 mg/kg/body mass) to moderate (6 mg/kg/body mass) doses are used [4,9,16]. The results of several studies indicated that habitual use of CAF may reduce the ergogenic effects of such doses [12,15,[17][18][19]. ...
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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.
... The ergogenic effect of caffeine is obtained in doses ranging between 3 and 9 mg/kg. However, the authors of this study recommend the use of 3 mg/kg of caffeine to obtain performance benefits as the frequency and magnitude of caffeine adverse effects are higher with 9 mg/kg of caffeine [50]. The use of an accurate dose of caffeine in mg per kg of participant's body mass is probably more important than the source of caffeine. ...
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Purpose The ergogenic effect of oral caffeine administration on short-term all-out exercise performance is well established. However, the potential mechanisms associated with caffeine’s ergogenicity in this type of exercise are poorly understood. The aim of this study was to investigate whether caffeine intake modifies muscle oxygen saturation during the 15-s Wingate Anaerobic Test. Methods Fifteen moderately trained individuals (body mass = 67.4 ± 12.3 kg; height 171.3 ± 6.9 cm; age 31 ± 6 years) took part in two identical experimental trials after the ingestion of (a) 3 mg/kg of caffeine or (b) 3 mg/kg of cellulose (placebo). After 60 min for substances absorption, participants performed a 15-s Wingate test on a cycle ergometer against a load representing 7.5% of participant’s body mass. Muscle oxygen saturation was continuously measured during exercise with near-infrared spectroscopy and blood lactate concentration was measured 1 min after exercise. Results In comparison to the placebo, the oral administration of caffeine increased peak power by 2.9 ± 4.5% (from 9.65 ± 1.38 to. 9.92 ± 1.40 W/kg, P = 0.038; effect size (ES), 95% confidence intervals = 0.28, 0.05–0.51), mean power by 3.5 ± 6.2% (from 8.30 ± 1.08 to 8.57 ± 1.12 W/kg, P = 0.044; ES = 0.36, 0.01–0.71) and blood lactate concentration by 20.9 ± 24.7% (from 12.4 ± 2.6 to 14.8 ± 4.0 mmol/L, P = 0.005; ES = 0.59, 0.16–1.02). However, caffeine did not modify the curve of muscle oxygen desaturation during exercise (lowest value was 23.1 ± 14.1 and 23.4 ± 14.1%, P = 0.940). Conclusion Caffeine’s ergogenic effect during short-term all-out exercise seems to be associated with an increased glycolytic metabolism with no influence of enhanced muscle oxygen saturation.
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Abbreviations: CAF: Caffeine PLC: Placebo SRT: Simple Reaction Time AT: Attention Test SJ: Squat Jump IAT: Illinois Agility Test OT: Oral Temperature QUEST: Questionnaire RPE: Rating of Perceived Exertion PD: Peak Distance TD: Total Distance.
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The interest in the benefits of caffeine in combat sports has grown exponentially in the last few years, evidenced by the significant rise of post-competition urine caffeine concentration. We conduct a systematic review and meta-analysis on the effects of caffeine on different performance variables in combat sports athletes. In total, we included 25 studies. All studies included had blinded, and cross-over experimental designs, and we conducted a risk of bias analysis. For nonspecific outcomes, there was an ergogenic effect of caffeine on vertical jump height (SMD: 0.38; 95% CI: 0.04, 0.71) and reaction time (SMD: -1.08, 95% CI: -1.51, -0.66). For outcomes specific to combat sports, there was an increase in the number of throws with caffeine in the Special Judo Fitness Test (SMD: 0.62; 95% CI: 0.14, 1.09). Caffeine ingestion increased the number of offensive actions during combats (SMD: 0.40; 95% CI: 0.06, 0.74). Caffeine ingestion increased the duration of offensive actions during combat (SMD: 0.58; 95% CI: 0.21, 0.96). Finally, caffeine ingestion increased blood lactate concentration after bout 1 (SMD: 1.35) bout 2 (SMD: 1.43) and bout 3 (SMD: 1.98). Overall, athletes competing in combat sports may consider supplementing with caffeine for an acute increase in exercise performance.
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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.
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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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The purpose of the present study was to examine the influence of muscle group location and gender on the reliability of assessing the one-repetition maximum (1RM) test. Thirty healthy males (n = 15) and females (n = 15) who experienced at least 3 months of continuous resistance training during the last 2 years aged 18-35 years volunteered to participate in the study. The 1RM for the biceps curl, lat pull down, bench press, leg curl, hip flexion, triceps extension, shoulder press, low row, leg extension, hip extension, leg press and squat were measured twice by a trained professional using a standard published protocol. Biceps curl, lat pull down, bench press, leg curl, hip flexion, and squat 1RM's were measured on the first visit, then 48 hours later, subjects returned for their second visit. During their second visit, 1RM of triceps extension, shoulder press, low row, leg extension, hip extension, and leg press were measured. One week from the second visit, participants completed the 1 RM testing as previously done during the first and second visits. The third and fourth visits were separated by 48 hours as well. All four visits to the laboratory were at the same time of day. A high intraclass correlation coefficient (ICC > 0.91) was found for all exercises, independent of gender and muscle group size or location, however there was a significant interaction for muscle group location (upper body vs. lower body) in females (p < 0.027). In conclusion, a standardized 1RM testing protocol with a short warm-up and familiarization period is a reliable measurement to assess muscle strength changes regardless of muscle group location or gender.
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Purpose: The aim of this study was to examine the effects of caffeine supplementation on multiple sprint running performance. Methods: Using a randomized double-blind research design, 21 physically active men ingested a gelatin capsule containing either caffeine (5 mg·kg-1 body mass) or placebo (maltodextrin) 1 h before completing an indoor multiple sprint running trial (12 × 30 m; repeated at 35-s intervals). Venous blood samples were drawn to evaluate plasma caffeine and primary metabolite concentrations. Sprint times were recorded via twin-beam photocells, and earlobe blood samples were drawn to evaluate pretest and posttest lactate concentrations. Heart rate was monitored continuously throughout the tests, with RPE recorded after every third sprint. Results: Relative to placebo, caffeine supplementation resulted in a 0.06-s (1.4%) reduction in fastest sprint time (95% likely range = 0.04-0.09 s), which corresponded with a 1.2% increase in fatigue (95% likely range = 0.3-2.2%). Caffeine supplementation also resulted in a 3.4-bpm increase in mean heart rate (95% likely range = 0.1-6.6 bpm) and elevations in pretest (+0.7 mmol·L-1; 95% likely range = 0.1-1.3 mmol·L-1) and posttest (+1.8 mmol·L-1; 95% likely range = 0.3-3.2 mmol·L-1) blood lactate concentrations. In contrast, there was no significant effect of caffeine supplementation on RPE. Conclusion: Although the effect of recovery duration on caffeine-induced responses to multiple sprint work requires further investigation, the results of the present study show that caffeine has ergogenic properties with the potential to benefit performance in both single and multiple sprint sports.
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To investigate whether caffeine ingestion counteracts the morning reduction in neuromuscular performance associated with the circadian rhythm pattern. Twelve highly resistance-trained men underwent a battery of neuromuscular tests under three different conditions; i) morning (10:00 a.m.) with caffeine ingestion (i.e., 3 mg kg(-1); AM(CAFF) trial); ii) morning (10:00 a.m.) with placebo ingestion (AM(PLAC) trial); and iii) afternoon (18:00 p.m.) with placebo ingestion (PM(PLAC) trial). A randomized, double-blind, crossover, placebo controlled experimental design was used, with all subjects serving as their own controls. The neuromuscular test battery consisted in the measurement of bar displacement velocity during free-weight full-squat (SQ) and bench press (BP) exercises against loads that elicit maximum strength (75% 1RM load) and muscle power adaptations (1 m s(-1) load). Isometric maximum voluntary contraction (MVC(LEG)) and isometric electrically evoked strength of the right knee (EVOK(LEG)) were measured to identify caffeine's action mechanisms. Steroid hormone levels (serum testosterone, cortisol and growth hormone) were evaluated at the beginning of each trial (PRE). In addition, plasma norepinephrine (NE) and epinephrine were measured PRE and at the end of each trial following a standardized intense (85% 1RM) 6 repetitions bout of SQ (POST). In the PM(PLAC) trial, dynamic muscle strength and power output were significantly enhanced compared with AM(PLAC) treatment (3.0%-7.5%; p≤0.05). During AM(CAFF) trial, muscle strength and power output increased above AM(PLAC) levels (4.6%-5.7%; p≤0.05) except for BP velocity with 1 m s(-1) load (p = 0.06). During AM(CAFF), EVOK(LEG) and NE (a surrogate of maximal muscle sympathetic nerve activation) were increased above AM(PLAC) trial (14.6% and 96.8% respectively; p≤0.05). These results indicate that caffeine ingestion reverses the morning neuromuscular declines in highly resistance-trained men, raising performance to the levels of the afternoon trial. Our electrical stimulation data, along with the NE values, suggest that caffeine increases neuromuscular performance having a direct effect in the muscle.
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The aims of this study were to evaluate the effects of caffeine supplementation on sprint cycling performance and to determine if there was a dose-response effect. Using a randomized, double-blind, placebo-controlled design, 17 well-trained men (age: 24 ± 6 years, height: 1.82 ± 0.06 m, and body mass(bm): 82.2 ± 6.9 kg) completed 7 maximal 10-second sprint trials on an electromagnetically braked cycle ergometer. Apart from trial 1 (familiarization), all the trials involved subjects ingesting a gelatine capsule containing either caffeine or placebo (maltodextrin) 1 hour before each sprint. To examine dose-response effects, caffeine doses of 2, 4, 6, 8, and 10 mg·kg bm(-1) were used. There were no significant (p ≥ 0.05) differences in baseline measures of plasma caffeine concentration before each trial (grand mean: 0.14 ± 0.28 μg·ml(-1)). There was, however, a significant supplement × time interaction (p < 0.001), with larger caffeine doses producing higher postsupplementation plasma caffeine levels. In comparison with placebo, caffeine had no significant effect on peak power (p = 0.11), mean power (p = 0.55), or time to peak power (p = 0.17). There was also no significant effect of supplementation on pretrial blood lactate (p = 0.58), but there was a significant time effect (p = 0.001), with blood lactate reducing over the 50 minute postsupplementation rest period from 1.29 ± 0.36 to 1.06 ± 0.33 mmol·L(-1). The results of this study show that caffeine supplementation has no effect on short-duration sprint cycling performance, irrespective of the dosage used.
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In this study we tested the hypothesis that caffeine supplementation improves neuromuscular function, which has both nutritional and clinical relevance. Fourteen male subjects (mean ± SD: 23.8 ± 2.8 years) volunteered in a double-blind, repeated-measures study with placebo (PLA) or caffeine (CAFF) (6 mg kg(-1)). Maximal voluntary isometric contractions (MVCs), evoked maximal twitch, and maximal isokinetic contractions during elbow flexion were assessed. Mechanical and electromyographic (EMG) signals from the biceps brachii muscle were recorded, and muscle fiber conduction velocity (CV) was calculated to evaluate changes in the muscle force-velocity relationship and muscle fiber recruitment. The torque-angular velocity curve was enhanced after CAFF supplementation. This was supported by a concomitant increase of CV values (8.7% higher in CAFF). Caffeine improves muscle performance during short-duration maximal dynamic contractions. The concomitant improvement of mean fiber CV supports the hypothesis of an effect of caffeine on motor unit recruitment.
Article
PURPOSE: The aims of this study were to evaluate the effects of caffeine supplementation on short-duration sprint cycling performance and to determine if there was a dose-response effect. METHODS: Using a randomised, double-blind, placebo-controlled design, 17 well-trained males (means ± standard deviation for age, height, body mass, and body fat of the subjects were: 24 ± 6 years, 1.82 ± 0.06 m, 82.2 ± 6.9 kg, and 13.5 ± 3.4%, respectively) completed seven maximal 10 s sprint trials on an electromagnetically-braked cycle ergometer, with a minimum of 48 hours between trials. Apart from Trial 1, which was used for familiarisation purposes, all trials required subjects to ingest a gelatine capsule containing either caffeine or placebo (maltodextrin) one hour prior to performing each sprint. To examine dose-response effects, the following doses of caffeine were used: 2, 4, 6, 8, and 10 mg·kg-1. RESULTS: The absence of significant differences in baseline measures of plasma caffeine concentration (established via high performance liquid chromatography) (grand mean: 0.14 ± 0.28 µg·ml-1; p = 0.30) confirmed subject compliance with caffeine abstinence prior to each trial. There was, as anticipated, a significant supplement × time interaction (p < 0.001) with larger caffeine doses producing higher post-supplementation plasma caffeine levels. In comparison with placebo, the results revealed no significant effect of supplementation on peak power (grand mean: 1135 ± 192 W; p = 0.11), mean power (grand mean: 774 ± 111 W; p = 0.55), or time to peak power (grand mean: 4.45 ± 1.16 s; p = 0.17). CONCLUSION: In contrast with the established benefits of caffeine supplementation on endurance performance, the results of this study show that caffeine supplementation has no effect on short-duration sprint cycling performance, irrespective of the dosage used
Article
This study aimed to analyze the acute mechanical and metabolic response to resistance exercise protocols (REP) differing in the number of repetitions (R) performed in each set (S) with respect to the maximum predicted number (P). Over 21 exercise sessions separated by 48-72 h, 18 strength-trained males (10 in bench press (BP) and 8 in squat (SQ)) performed 1) a progressive test for one-repetition maximum (1RM) and load-velocity profile determination, 2) tests of maximal number of repetitions to failure (12RM, 10RM, 8RM, 6RM, and 4RM), and 3) 15 REP (S × R[P]: 3 × 6[12], 3 × 8[12], 3 × 10[12], 3 × 12[12], 3 × 6[10], 3 × 8[10], 3 × 10[10], 3 × 4[8], 3 × 6[8], 3 × 8[8], 3 × 3[6], 3 × 4[6], 3 × 6[6], 3 × 2[4], 3 × 4[4]), with 5-min interset rests. Kinematic data were registered by a linear velocity transducer. Blood lactate and ammonia were measured before and after exercise. Mean repetition velocity loss after three sets, loss of velocity pre-post exercise against the 1-m·s load, and countermovement jump height loss (SQ group) were significant for all REP and were highly correlated to each other (r = 0.91-0.97). Velocity loss was significantly greater for BP compared with SQ and strongly correlated to peak postexercise lactate (r = 0.93-0.97) for both SQ and BP. Unlike lactate, ammonia showed a curvilinear response to loss of velocity, only increasing above resting levels when R was at least two repetitions higher than 50% of P. Velocity loss and metabolic stress clearly differs when manipulating the number of repetitions actually performed in each training set. The high correlations found between mechanical (velocity and countermovement jump height losses) and metabolic (lactate, ammonia) measures of fatigue support the validity of using velocity loss to objectively quantify neuromuscular fatigue during resistance training.
Article
The primary aim of the study was to determine the efficacy of acute caffeine intake to enhance intense resistance training performance. Fourteen resistance-trained men (age and body mass = 23.1 ± 1.1 years and 83.4 ± 13.2 kg, respectively) who regularly consumed caffeine ingested caffeine (6 mg · kg(-1)) or placebo 1 hour before completion of 4 sets of barbell bench press, leg press, bilateral row, and barbell shoulder press to fatigue at 70-80% 1-repetition maximum. Two minutes of rest was allotted between sets. Saliva samples were obtained to assess caffeine concentration. The number of repetitions completed per set and total weight lifted were recorded as indices of performance. Two-way analysis of variance with repeated measures was used to examine differences in performance across treatment and sets. Compared to placebo, there was a small but significant effect (p < 0.05) of acute caffeine intake on repetitions completed for the leg press but not for upper-body exercise (p > 0.05). Total weight lifted across sets was similar (p > 0.05) with caffeine (22,409.5 ± 3,773.2 kg) vs. placebo (21,185.7 ± 4,655.4 kg), yet there were 9 'responders' to caffeine, represented by a meaningful increase in total weight lifted with caffeine vs. placebo. Any ergogenic effect of caffeine on performance of fatiguing, total-body resistance training appears to be of limited practical significance. Additional research is merited to elucidate interindividual differences in caffeine-mediated improvements in performance.