ArticlePDF Available

Abstract and Figures

To determine whether the ergogenic effects of caffeine ingestion on neuromuscular performance are similar when ingestion takes place in the morning and in the afternoon. Double blind, cross-over, randomized, placebo controlled design. Thirteen resistance-trained males carried out bench press and full squat exercises against four incremental loads (25%, 50%, 75% and 90% 1RM), at maximal velocity. Trials took place 60min after ingesting either 6mgkg(-1) of caffeine or placebo. Two trials took place in the morning (AMPLAC and AMCAFF) and two in the afternoon (PMPLAC and PMCAFF), all separated by 36-48h. Tympanic temperature, plasma caffeine concentration and side-effects were measured. Plasma caffeine increased similarly during AMCAFF and PMCAFF. Tympanic temperature was lower in the mornings without caffeine effects (36.7±0.4 vs. 37.0±0.5°C for AM vs. PM; p<0.05). AMCAFF increased propulsive velocity above AMPLAC to levels similar to those found in the PM trials for the 25%, 50%, 75% 1RM loads in the SQ exercise (5.4-8.1%; p<0.05). However, in the PM trials, caffeine ingestion did not improve propulsive velocity at any load during BP or SQ. The negative side effects of caffeine were more prevalent in the afternoon trials (13 vs. 26%). The ingestion of a moderate dose of caffeine counteracts the muscle contraction velocity declines observed in the morning against a wide range of loads. Caffeine effects are more evident in the lower body musculature. Evening caffeine ingestion not only has little effect on neuromuscular performance, but increases the rate of negative side-effects reported.
Content may be subject to copyright.
Please
cite
this
article
in
press
as:
Mora-Rodríguez
R,
et
al.
Improvements
on
neuromuscular
performance
with
caffeine
ingestion
depend
on
the
time-of-day.
J
Sci
Med
Sport
(2014),
http://dx.doi.org/10.1016/j.jsams.2014.04.010
ARTICLE IN PRESS
G Model
JSAMS-1024;
No.
of
Pages
5
Journal
of
Science
and
Medicine
in
Sport
xxx
(2014)
xxx–xxx
Contents
lists
available
at
ScienceDirect
Journal
of
Science
and
Medicine
in
Sport
journal
h
om
epage:
www.elsevier.com/locate/jsams
Original
research
Improvements
on
neuromuscular
performance
with
caffeine
ingestion
depend
on
the
time-of-day
Ricardo
Mora-Rodrígueza,,
Jesús
G.
Pallarésa,
José
María
López-Gullónb,
Álvaro
López-Samanesa,
Valentín
E.
Fernández-Elíasa,
Juan
F.
Ortegaa
aExercise
Physiology
Laboratory
at
Toledo,
University
of
Castilla-La
Mancha,
Spain
bFaculty
of
Sport
Sciences,
University
of
Murcia,
Spain
a
r
t
i
c
l
e
i
n
f
o
Article
history:
Received
30
August
2013
Received
in
revised
form
8
April
2014
Accepted
17
April
2014
Available
online
xxx
Keywords:
Muscle
strength
Chronobiology
Circadian
rhythm
Body
temperature
Ergogenic
aid
Maximal
voluntary
contraction
a
b
s
t
r
a
c
t
Objectives:
To
determine
whether
the
ergogenic
effects
of
caffeine
ingestion
on
neuromuscular
perfor-
mance
are
similar
when
ingestion
takes
place
in
the
morning
and
in
the
afternoon.
Design:
Double
blind,
cross-over,
randomized,
placebo
controlled
design.
Methods:
Thirteen
resistance-trained
males
carried
out
bench
press
and
full
squat
exercises
against
four
incremental
loads
(25%,
50%,
75%
and
90%
1RM),
at
maximal
velocity.
Trials
took
place
60
min
after
ingesting
either
6
mg
kg1of
caffeine
or
placebo.
Two
trials
took
place
in
the
morning
(AMPLAC and
AMCAFF)
and
two
in
the
afternoon
(PMPLAC and
PMCAFF),
all
separated
by
36–48
h.
Tympanic
temperature,
plasma
caffeine
concentration
and
side-effects
were
measured.
Results:
Plasma
caffeine
increased
similarly
during
AMCAFF and
PMCAFF.
Tympanic
temperature
was
lower
in
the
mornings
without
caffeine
effects
(36.7
±
0.4
vs.
37.0
±
0.5 C
for
AM
vs.
PM;
p
<
0.05).
AMCAFF
increased
propulsive
velocity
above
AMPLAC to
levels
similar
to
those
found
in
the
PM
trials
for
the
25%,
50%,
75%
1RM
loads
in
the
SQ
exercise
(5.4–8.1%;
p
<
0.05).
However,
in
the
PM
trials,
caffeine
ingestion
did
not
improve
propulsive
velocity
at
any
load
during
BP
or
SQ.
The
negative
side
effects
of
caffeine
were
more
prevalent
in
the
afternoon
trials
(13
vs.
26%).
Conclusions:
The
ingestion
of
a
moderate
dose
of
caffeine
counteracts
the
muscle
contraction
veloc-
ity
declines
observed
in
the
morning
against
a
wide
range
of
loads.
Caffeine
effects
are
more
evident
in
the
lower
body
musculature.
Evening
caffeine
ingestion
not
only
has
little
effect
on
neuromuscular
performance,
but
increases
the
rate
of
negative
side-effects
reported.
©
2014
Sports
Medicine
Australia.
Published
by
Elsevier
Ltd.
All
rights
reserved.
1.
Introduction
Diurnal
variation
of
performance
oscillate,
with
higher
scores/output
being
obtained
at
midday
and
early
evening,
and
lower
ones
during
the
late
night
and
early
morning
hours.1,2 The
morning
reductions
in
performance
can
be
observed
during
com-
plex
motor
control
tasks
that
involve
integration
of
information
(e.g.,
tennis
serve3or
handwriting4)
as
well
as
during
simple
con-
tinuous
motor
tasks
(e.g.,
pedaling5or
swimming1).
The
changes
in
motor
performance
associated
with
circadian
rhythm
have
been
mostly
described
for
long-
and
medium-term
efforts,
which
depend
mainly
on
cardiorespiratory
endurance.1,6 However,
cir-
cadian
rhythm
could
also
affect
short-term
events
that
rely
on
Corresponding
author
at:
Universidad
de
Castilla-La
Mancha,
Avda,
Carlos
III,
s/n.
45071
Toledo,
Spain.
Tel.:
+34
925
26
88
00x5510;
fax:
+34
925
26
88
46.
E-mail
address:
Ricardo.Mora@uclm.es
(R.
Mora-Rodríguez).
maximal
muscle
strength
and
power
output.7,8 In
a
limited
num-
ber
of
studies,
researchers
have
actually
manipulated
some
of
the
factors
involved
in
this
biological
rhythm.
Some
investigators
have
increased
morning
body
temperature
by
passive
heating9or
active
warm-up10,11 since
it
has
been
hypothesized
that
the
diurnal
increase
in
body
temperature
mediates
the
improvements
in
mus-
cle
contractility.
In
these
studies
the
authors
observed
improved
performance
with
body
warming
although
motor
performance
did
not
completely
return
to
the
levels
found
in
the
afternoon.
Caffeine
(CAFF)
is
an
ergogenic
aid
commonly
used
by
elite
and
recreational
athletes.12 The
ergogenic
effect
of
caffeine
on
endurance
performance
is
well
recognized
and
has
been
ana-
lyzed
at
length.13 In
addition,
caffeine
has
been
shown
to
improve
the
number
of
repetitions
to
failure
(muscle
endurance14,15)
and
muscle
power
in
large
muscle
groups
when
using
submaximal
loads.16,17 Since
muscle
strength
is
decreased
in
the
morning18,19
and
caffeine
could
potentially
increase
muscle
strength
and
power,20 we
have
recently
examined
whether
caffeine
ingestion
http://dx.doi.org/10.1016/j.jsams.2014.04.010
1440-2440/©
2014
Sports
Medicine
Australia.
Published
by
Elsevier
Ltd.
All
rights
reserved.
Please
cite
this
article
in
press
as:
Mora-Rodríguez
R,
et
al.
Improvements
on
neuromuscular
performance
with
caffeine
ingestion
depend
on
the
time-of-day.
J
Sci
Med
Sport
(2014),
http://dx.doi.org/10.1016/j.jsams.2014.04.010
ARTICLE IN PRESS
G Model
JSAMS-1024;
No.
of
Pages
5
2
R.
Mora-Rodríguez
et
al.
/
Journal
of
Science
and
Medicine
in
Sport
xxx
(2014)
xxx–xxx
could
reverse
the
morning
neuromuscular
weakening.16 We
found
that
a
low
dose
of
caffeine
(3
mg
kg1)
ingested
in
the
morning
could
increase
contraction
velocity
against
a
70%
1RM
load.
How-
ever,
we
did
not
provide
caffeine
in
an
extra
afternoon
trial.
That
trial
is
needed
to
ensure
that
the
caffeine
effects
in
the
morning
were
not
also
present
in
the
afternoon
and
thus
not
related
to
cir-
cadian
rhythm.16 In
addition,
there
is
limited
information
regarding
the
side-effects
of
the
caffeine
doses
usually
ingested
for
improv-
ing
sports
performance
(2–9
mg
kg1).
A
recent
study
suggests
that
caffeine
ingestion
in
doses
higher
than
6
mg
kg1is
prone
to
pro-
duce
adverse
side-effects.17 Nevertheless,
the
possible
side-effects
associated
with
caffeine
ingestion
of
these
ergogenic
doses
in
the
afternoon
remain
unknown.
Therefore,
the
main
purpose
of
this
study
is
to
determine
if
caf-
feine
ingestion
at
a
moderate
dose
(6
mg
kg1)
could
reverse
the
morning
reductions
in
neuromuscular
performance
in
resistance-
trained
athletes.
We
also
sought
to
determine
if
caffeine
ingested
in
the
afternoon
produces
additional
neuromuscular
enhancements
compared
to
caffeine
ingestion
in
the
morning.
We
believe
that
this
information
is
relevant,
as
caffeine
is
widely
being
used
as
an
ergogenic
aid,
despite
the
lack
of
information
about
whether
its
effects
are
similar
when
ingested
in
the
morning
or
the
afternoon.
Additionally,
we
examined
the
side-effects
associated
with
caffeine
ingestion
according
to
time-of-day
and
their
possible
implications
for
athletes’
performance
and
recovery.
2.
Methods
Thirteen
highly
resistance-trained
men
volunteered
to
par-
ticipate
in
this
study
(age
21.9
±
2.9
yr,
body
mass
76.5
±
8.5
kg,
height
172.7
±
5.4
cm,
body
fat
12.4
±
2.7%,
resistance
training
experience
7.1.±.3.5
yr).
Their
1RM
strength
for
the
free-weight
full-squat
(SQ)
and
bench
press
(BP)
exercises
was
112.5
±
12.6
kg
and
121.0
±
22.7
kg,
respectively.
The
study
complied
with
the
Dec-
laration
of
Helsinki
and
was
approved
by
the
Bioethics
Commission
of
the
University
of
Murcia.
Prior
to
participation,
written
informed
consent
was
obtained
from
each
athlete.
A
validated
caffeine
consumption
questionnaire
was
used
to
document
the
subjects’
self-reported
habitual
caffeine
consumption.21 The
results
showed
that
all
participants
were
light
caffeine
consumers
(70
mg
day1).
A
randomized,
double-blind,
crossover,
placebo
controlled
experimental
design
was
used.
Participants
underwent
the
same
battery
of
neuromuscular
and
biochemical
assessments
under
four
different
conditions:
(i)
morning
(8:00
a.m.)
with
caffeine
ingestion
(6
mg
kg1;
AMCAFF);
(ii)
morning
(8:00
a.m.)
with
placebo
inges-
tion
(AMPLAC);
(iii)
afternoon
(18:00
p.m.)
with
caffeine
ingestion
(6
mg
kg1;
PMCAFF);
and
(iv)
afternoon
(18:00
p.m.)
with
placebo
ingestion
(PMPLAC).
The
trials
were
separated
by
36–48
h
to
allow
complete
recovery
and
caffeine
washout.22 In
the
caffeine
inges-
tion
treatments,
caffeine
(Durvitan,
Seid,
Spain)
was
provided
in
gelatine
capsules
individually
filled
to
deliver
a
dose
of
6
mg
kg1
body
mass.
The
capsules
were
ingested
60
min
before
the
testing
to
coincide
with
peak
blood
caffeine
levels.23 In
trials
without
caf-
feine
ingestion
(AMPLAC and
PMPLAC)
participants
ingested
placebo
capsules
filled
with
the
same
amount
of
dextrose
(2
kcal)
to
avoid
identification.
All
subjects
had
previously
participated
in
experiments
involv-
ing
all
the
muscle
strength
and
power
tests
performed
in
this
study.
Nevertheless,
participants
underwent
7
familiarization
ses-
sions
before
the
start
of
the
experimental
trials
to
avoid
the
bias
of
progressive
learning.
The
last
familiarization
session,
performed
in
the
morning
(8:00
h)
of
the
third
day
prior
to
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
participant.17
The
day
before
and
during
the
six
days
that
the
experiment
lasted,
the
participants
stayed
in
a
sports
performance
center
where
they
slept
and
ate
all
their
meals.
They
consumed
a
diet
of
2800–3000
kcal
day1composed
of
55%
energy
intake
from
car-
bohydrates,
25%
from
fat
and
20%
from
protein,
evenly
distributed
across
three
meals
each
day
(breakfast
at
7:00
h,
lunch
at
13:30
h
and
dinner
at
20:00
h).
Participants
refrained
from
physical
activity
other
than
that
required
in
the
experimental
trials
and
withdrew
from
alcohol,
tobacco
and
caffeine
10
days
before
testing
and
while
the
experiment
lasted.
Upon
arrival
at
the
testing
room
at
6:30
h
in
a
fasted
state
a
urine
sample
(15
mL)
was
obtained
and
urine
specific
gravity
(USG;
Uricon-NE,
Atago,
Japan)
was
measured.
The
remaining
urine
was
frozen
at
20 C
for
subsequent
analysis.
Then,
the
partic-
ipants’
body
weight
was
determined
and
body
water
estimated
using
a
body
composition
bio-impedance
analyzer
(Tanita
TBF-
300A,
Tanita
Corp.,
Tokyo,
Japan).
Following
this,
the
tympanic
temperature
(Thermoscan,
Braun,
Germany)
was
measured
in
trip-
licate
after
the
removal
of
earwax
when
necessary.
After
15
min
of
supine
rest
on
a
stretcher,
a
9
mL
blood
sample
was
withdrawn
from
an
antecubital
vein
without
stasis.
A
small
portion
of
the
whole
blood
was
used
to
determine
hematocrit
by
triplicate
using
no-heparinized
capillary
tubes
(70
L;
Hirschmann
Laborgerate;
Germany)
and
a
micro-centrifuge
(Biocen,
Arlesa,
Spain).
The
rest
of
the
blood
was
centrifuged
(3000
g)
and
the
plasma
obtained
was
stored
at
70 C.
Participants
ingested
the
capsules
containing
their
individualized
caffeine
dose
or
placebo
with
330
mL
of
a
fruit
milk-
shake
and
a
pastry
that
served
as
a
standardized
breakfast
in
the
AM
trials
or
as
an
afternoon
snack
in
the
PM
trials
(total
of
624
kcal
and
68
g
of
carbohydrate).
After
a
standard
warm-up
(10
min
of
jogging
and
10
min
of
static
stretches)
participants
started
the
neuromuscular
test
battery
con-
sisting
of
the
measurement
of
bar
displacement
velocity
against
4
incremental
loads
(25%,
50%,
75%
and
90%
of
1RM)
for
upper
and
lower
body
musculature
(BP
and
SQ).
Upon
completion
of
the
test
battery
(60
min)
a
second
urine
and
blood
samples
were
col-
lected.
Then,
participants
filled
out
a
side-effects
questionnaire
that
was
also
collected
24
h
after
each
trial.
Blood
hematocrit,
USG,
tym-
panic
temperature
and
blood
and
urine
caffeine
concentration
and
its
related
metabolites
(i.e.,
paraxanthine,
theophylline
and
theo-
bromine)
were
evaluated
before
(PRE)
and
after
(POST)
each
trial.
Two
identical
Smith
machines
(Multipower
Fitness
Line,
Peroga,
Spain),
each
dedicated
to
a
given
exercise
(SQ
or
BP),
and
equipped
with
linear
velocity
transducers
(T-Force
System,
Ergotech,
Mur-
cia,
Spain;
0.25%
accuracy;
ICC
=
1.00;
CV
=
0.57%)
were
used.
Bar
velocity
against
the
individually
determined
25%,
50%,
75%
and
90%
of
1RM
loads
were
measured
under
the
four
experimental
condi-
tions.
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
repetition
at
each
load,
according
to
the
criteria
of
fastest
mean
propulsive
velocity
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
tele-
scopic
bar
holders
with
a
precision
of
±1.0
cm.
After
the
eccentric
phase,
participants
momentarily
released
the
weight
of
the
bar
in
the
holders
for
2
s
to
thereafter
perform
a
purely
concentric
action
at
maximal
velocity.
This
was
designed
to
minimize
the
contribu-
tion
of
the
stretch-shortening
cycle
(i.e.
rebound
effect)
increasing
measurement
reliability.24
Urine
and
plasma
samples
were
analyzed
for
caffeine
concen-
trations
and
related
metabolites
using
an
Agilent
Technologies
HPLC
1200
system
(Santa
Clara,
CA,
US)
coupled
to
a
triple
quadrupole/ion
trap
mass
spectrometer
(MS;
API
4000,
Q
TRAP,
US).
Methylxanthines
internal
standards
were
purchased
from
Cer-
illiant
(Texas,
USA).
To
calibrate
the
system,
aqueous
solutions
of
Please
cite
this
article
in
press
as:
Mora-Rodríguez
R,
et
al.
Improvements
on
neuromuscular
performance
with
caffeine
ingestion
depend
on
the
time-of-day.
J
Sci
Med
Sport
(2014),
http://dx.doi.org/10.1016/j.jsams.2014.04.010
ARTICLE IN PRESS
G Model
JSAMS-1024;
No.
of
Pages
5
R.
Mora-Rodríguez
et
al.
/
Journal
of
Science
and
Medicine
in
Sport
xxx
(2014)
xxx–xxx
3
caffeine
(ranging
from
0.25
to
12
g
mL1)
and
paraxanthine,
theo-
bromine
and
theophylline
(from
0.5
to
30
g
mL1)
were
used
for
each
batch
of
samples.
The
lower
limit
for
the
accurate
quantization
of
these
methylxanthines
was
0.25
g
mL1.
All
urine
and
blood
determinations
were
assessed
according
to
the
current
World
Anti-
Doping
Agency’s
standards,
protocols
and
instruments
established
to
detect
patterns
of
misuse
of
this
substance
in
sport
through
the
Monitoring
Program.
The
intra-day
and
between-day
coefficient
of
variations
ranged
between
2.8–5.6%,
2.2–9.7%,
2.4–10.9%,
2.0–9.8%
for
caffeine,
paraxanthine,
theobromine
and
theophylline,
respec-
tively.
Participants
answered
a
questionnaire
to
evaluate
their
perceived
performance,
physical
and
cognitive
fatigue
and
the
adverse
side
effects
(e.g.,
urine
output,
gastrointestinal
problems,
tachycardia,
or
headache)
immediately
after
each
neuromuscular
test
battery
(QUEST
+
0
h)
and
24
h
later
(QUEST
+
24
h).
These
sur-
veys
included
eight
items
on
a
yes/no
scale
and
were
based
on
previous
publications
about
side
effects
derived
from
the
ingestion
of
caffeine.12,17
The
Shapiro–Wilk
test
was
used
to
assess
normal
distribution
of
data.
Data
were
analyzed
using
two-way
(caffeine
treatment
×
time
of
day)
ANOVA
for
repeated
measures.
The
Greenhouse–Geisser
adjustment
for
sphericity
was
calculated.
After
a
significant
F
test
for
the
interaction
effect,
differences
among
means
were
identified
using
pairwise
comparisons
with
Bonferroni’s
adjustment.
The
sig-
nificance
level
was
set
at
p
0.05.
Cohen’s
formula
for
effect
size
(ES)
was
used,
and
the
results
were
based
on
the
following
criteria;
>0.70
large
effect;
0.30–0.69
moderate
effect;
0.30
small
effect.
Side-effects
stated
in
the
questionnaires
by
the
participants
were
not
normally
distributed
and
were
reported
throughout
a
descrip-
tive
analysis
as
percentage
of
prevalence.
3.
Results
Before
trials
body
mass
(range
76.9
±
8.1–76.4
±
8.5
kg),
bio-
impedance
(range
464
±
48–475
±
54
),
hematocrit
and
USG were
not
different
between
trials.
Before
exercise
(PRE),
tympanic
tem-
perature
(Ttym)
in
the
two
PM
trials
was
significantly
elevated
(1.0–1.2%;
p
=
0.000–0.048;
ES
=
0.97–1.32)
when
compared
to
the
AM
values.
When
PRE
and
POST
testing
conditions
were
com-
pared,
Ttym
increased
in
all
trials
except
in
PMPLAC (1.5–1.7%;
p
=
0.02–0.04;
ES
=
1.10–1.50).
Hematocrit
was
higher
in
the
morn-
ings
than
in
the
afternoon
trials
when
caffeine
and
non-caffeine
trials
were
pooled
(45.6
±
3.6%
vs.
44.8
±
3.3%)
and
increased
with
exercise
except
for
AMPLAC (3.7–4.7%;
p
=
0.004–0.000;
ES
=
0.50–0.61;
Table
1).
Immediately
after
the
caffeine
trials,
par-
ticipants
increased
their
perception
of
performance
and
vigor
compared
to
PLAC
while
negative
side-effects
were
kept
at
a
low
rate
(8–15%),
except
urine
output
in
the
PMCAFF treatment
(38%).
Twenty-four
hours
after
the
AMCAFF trial
the
side-effects
were
low
and
similar
to
AMPLAC.
However,
24
h
after
PMCAFF vigor
was
ele-
vated,
but
so
were
insomnia
and
anxiety
compared
to
the
PMPLAC
and
AMCAFF (Table
2).
Compared
to
the
morning
placebo
trial
(AMPLAC),
mean
propul-
sive
velocity
for
25%,
50%
and
75%
1RM
load
in
the
SQ
exercise
was
higher
in
both
caffeine
trials
(AMCAFF and
PMCAFF)
and
in
the
evening
placebo
trial
(PMPLAC)
(5.4–8.5%;
p
=
0.037–0.000;
ES
=
0.75–1.16).
No
significant
differences
(p
>
0.05)
among
means
were
detected
between
both
caffeine
(AMCAFF and
PMCAFF)
and
the
afternoon
placebo
trial
(PMPLAC).
Although
no
significant
caffeine
treatment
by
time
of
day
interaction
was
found
in
the
BP
exercise,
important
percentage
elevations
and
effect
sizes
were
detected
for
AMCAFF,
PMPLAC and
PMCAFF when
compared
to
the
AMPLAC trial
in
all
loads
(4.8–9.4%;
ES
=
0.51–0.99;
Fig.
1).
Fig.
1.
Effects
of
time-of-day
and
caffeine
ingestion
on
load-velocity
relationship
for
bench
press
(A)
and
full
squat
(B)
exercises.
Data
are
means
±
SD.
*Significant
difference
(p
0.05)
compared
to
the
AMPLAC trail.
PRE
plasma
and
urine
caffeine
and
paraxanthine
concentrations
were
very
low
in
all
participants
confirming
complete
caffeine
washout
before
trials.
After
the
two
caffeine
trials
(AMCAFF and
PMCAFF)
urine
and
plasma
caffeine
and
paraxanthine
concentra-
tions
were
higher
(p
<
0.05)
than
their
respective
PRE
values.
The
concentrations
after
the
caffeine
trials
were
also
higher
than
their
respective
POST
placebo
values,
except
for
paraxanthine
urine
con-
centration
in
PMPLAC (p
=
0.07–0.10).
Urine
and
plasma
theophylline
and
theobromine
concentrations
did
not
show
any
statistical
inter-
action
with
the
circadian
rhythm
pattern
or
caffeine
ingestion
(Table
1).
4.
Discussion
The
main
finding
of
this
study
is
that
the
morning
ingestion
of
a
moderate
dose
of
caffeine
(6
mg
kg1)
significantly
improves
movement
velocity
at
loads
from
25%
to
75%
1RM
in
the
lower
body
musculature
(SQ)
of
resistance-trained
individuals.
Caffeine
ingestion
in
the
morning
increases
movement
velocity
to
the
levels
found
in
the
afternoon.
However,
caffeine
ingestion
in
the
late
after-
noon
does
not
affect
movement
velocity
at
any
load,
neither
in
the
upper
nor
in
the
lower
body.
When
caffeine
is
ingested
in
the
morn-
ing
(i.e.,
AMCAFF),
the
prevalence
of
adverse
side-effects
during
the
trial
and
in
the
following
24
h
is
low
(Table
2).
Conversely,
follow-
ing
the
caffeine
ingestion
in
the
afternoon
(PMCAFF),
participants
reported
some
important
adverse
side-effects
such
as
insomnia
and
nervousness
that
could
negatively
affect
cognitive
and
phys-
ical
performance
if
the
sport
event
lasts
more
than
a
few
hours.
Please
cite
this
article
in
press
as:
Mora-Rodríguez
R,
et
al.
Improvements
on
neuromuscular
performance
with
caffeine
ingestion
depend
on
the
time-of-day.
J
Sci
Med
Sport
(2014),
http://dx.doi.org/10.1016/j.jsams.2014.04.010
ARTICLE IN PRESS
G Model
JSAMS-1024;
No.
of
Pages
5
4
R.
Mora-Rodríguez
et
al.
/
Journal
of
Science
and
Medicine
in
Sport
xxx
(2014)
xxx–xxx
Table
1
Effects
of
time-of-day
and
caffeine
ingestion
on
temperature,
hydration
status
markers
and
urine
and
plasma
concentrations
of
caffeine
and
metabolites
before
and
after
the
trials
(PRE-POST).
AMPLAC AMCAFF PMPLAC PMCAFF
PRE
POST
PRE
POST
PRE
POST
PRE
POST
Tympanic
temperature
(C)
36.2
±
0.6*36.8
±
0.4
36.3
±
0.4*36.8
±
0.5
36.7
±
0.4a,b 36.9
±
0.6
36.7
±
0.4*,a,b37.3
±
0.5c,d
Hematocrit
(%) 44.9
±
3.2 46.3
±
3.6 45.7
±
3.5*47.4
±
3.3
44.7
±
3.3*46.8
±
3.6
44.7
±
3.3*46.4
±
3.9
Urine
specific
gravity
1.024
±
0.005
1.019
±
0.007
1.022
±
0.005
1.018
±
0.005
1.021
±
0.007
1.015
±
0.010
1.019
±
0.006
1.018
±
0.08
Urine
caffeine
(g
mL1)
0.08
±
0.15
0.06
±
0.09
0.03
±
0.05*3.00
±
0.94c,e0.14
±
0.17
0.17
±
0.22
0.18
±
0.30*2.59
±
1.17c,e
Urine
paraxanthine
(g
mL1)
2.15
±
2.74
1.20
±
1.69
1.27
±
1.23*4.33
±
1.48c2.90
±
2.78
2.34
±
2.82
2.20
±
3.10*5.52
±
4.29c
Urine
theophylline
(g
mL1)
0.19
±
0.18
0.11
±
0.11
0.10
±
0.11
0.23
±
0.10
0.32
±
0.33
0.21
±
0.23
0.38
±
0.47
0.41
±
0.43
Urine
theobromine
(g
mL1)
8.82
±
9.12
7.11
±
4.94
9.65
±
9.40
9.41
±
5.39
7.74
±
5.47
6.91
±
4.68
7.77
±
7.13
9.52
±
6.84
Plasma
caffeine
(g
mL1) 0.10
±
0.06 0.15
±
0.07 0.07
±
0.04*4.14
±
0.60c,e0.25
±
0.21
0.21
±
0.15
0.27
±
0.55*4.02
±
0.90c,e
Plasma
paraxanthine
(g
mL1) 0.16
±
0.12 0.12
±
0.08 0.11
±
0.12*1.00
±
0.25c,e0.47
±
0.42
0.35
±
0.31
0.33
±
0.43*1.03
±
0.44c,e
Plasma
theophylline
(g
mL1)
0.05
±
0.09
0.02
±
0.04
0.05
±
0.11
0.07
±
0.03
0.09
±
0.09
0.08
±
0.08
0.08
±
0.15
0.11
±
0.08
Plasma
theobromine
(g
mL1)
1.52
±
1.04*2.83
±
1.28
2.22
±
1.99
3.37
±
1.13
1.89
±
1.29*2.51
±
1.11
1.17
±
0.61*2.59
±
0.89
Data
are
means
±
SD.
*Significantly
different
(p
0.05)
when
comparing
to
their
respective
POST
value.
aSignificantly
different
(p
0.05)
when
comparing
to
AMPLAC PRE.
bSignificantly
different
(p
0.05)
when
comparing
to
AMCAFF PRE.
cSignificantly
different
(p
0.05)
when
comparing
to
AMPLAC POST.
dSignificantly
different
(p
0.05)
when
comparing
to
AMCAFF POST.
eSignificantly
different
(p
0.05)
when
comparing
to
PMPLAC POST.
We
consider
that
these
two
findings
have
practical
applications
for
sport
nutrition
and
performance.
Some
of
the
studies
in
which
caffeine
ingestion
is
found
to
be
ergogenic
have
been
conducted
in
the
mornings25,26 while
many
of
them
do
not
detail
the
time-of-day
of
caffeine
ingestion.
We
found
that
caffeine
at
a
dose
of
6
mg
kg1has
little
effects
on
maximal
voluntary
contractions
when
ingested
in
the
afternoon,
while
it
increases
mean
propulsive
velocity
in
the
morning.
It
is
possible
that
some
of
the
literature
controversy
concerning
caffeine
as
an
ergogenic
aid
could
be
due
to
the
time-of-day
when
caffeine
was
ingested.
Our
data
suggest
that
the
time-of-day
of
caffeine
intake
is
a
confounding
variable
that
should
be
taken
into
consideration
when
studying
the
ergogenic
effects
of
caffeine.
The
mechanisms
behind
this
time
related
effect
of
caffeine
in
muscle
performance
is
not
clear.
A
recent
meta-analysis
revealed
that
caffeine
has
a
stronger
effect
in
maximal
voluntary
contraction
in
large
muscle
groups
than
in
small
ones.27 It
has
been
speculated
that
the
reason
for
this
difference
is
that
neural
activation
is
almost
complete
when
recruiting
a
smaller
muscle
mass
and
thus
there
is
little
opportu-
nity
for
caffeine
to
improve
contraction
force.27 This
could
explain
our
current
finding
of
statistical
significant
effects
of
caffeine
dur-
ing
SQ
exercise
(large
muscle
mass)
while
not
reaching
significance
during
BP
exercise
(smaller
muscle
mass).
A
similar
rationale
may
apply
to
the
morning-afternoon
situation.
In
the
morning
there
is
a
reduced
capacity
to
recruit
or
activate
the
musculature
and
thus
a
stimulant
like
caffeine
with
effects
on
the
central
nervous
system28
and
the
local
musculature29 could
increase
contraction
force.
Core
temperature
and
muscle
power
fluctuate
synchronously
during
the
day
with
a
lower
point
at
6:00
h
and
an
acrophase
in
the
late
afternoon.1,18 This
has
led
some
authors
to
speculate
that
the
increases
in
body
temperature
from
morning
to
afternoon
could
be
behind
the
improved
muscle
contractility
and
overall
perfor-
mance
in
the
afternoon.11,19 Interestingly,
the
higher
muscle
forces
observed
in
the
afternoon
happened
without
modification
of
mus-
cle
electrical
activity
(EMG).9This
suggests
that
the
improvement
in
muscle
force
in
the
afternoon
is
not
due
to
modifications
in
neural
drive
but
rather
to
improvements
of
muscle
contractile
properties
linked
to
body
temperature.
Our
experiment
was
conducted
in
a
thermoneutral
environment
(18 C)
and
the
standardized
warm-up
was
not
enough
to
elevate
tympanic
temperature
in
the
morning
to
the
levels
of
the
afternoon
trials.
Furthermore,
caffeine
inges-
tion
had
no
effect
on
tympanic
temperature
or
hydration
status
markers
(hematocrit
or
USG;
Table
1).
Thus,
the
increased
morn-
ing
neuromuscular
performance
after
caffeine
consumption
in
the
present
study
was
not
mediated
by
increased
body
temperature.
The
morning
caffeine
performance
enhancement
could
be
gener-
ated
by
caffeine
direct
actions
in
the
muscle
contractile
apparatus
as
has
been
found
using
muscle
electrostimulation.16,29
Data
is
scarce
regarding
the
side-effects
of
the
caffeine
doses
usually
ingested
for
improving
sports
performance
(1–9
mg
kg1).
In
a
descriptive
cross-sectional
study,
Desbrow
and
Leveritt12
found
very
minor
adverse
caffeine
related
symptoms
during
an
Ironman
competition.
However,
in
a
recent
study
we
reported
that
caffeine
ingestion
of
doses
9
mg
kg1in
the
morning
is
prone
to
produce
adverse
side-effects
such
as
tachycardia,
anxiety,
gastroin-
testinal
problems
and
especially
insomnia
or
sleep
disturbances
in
35–40%
of
the
subjects.17 In
the
present
study
we
observe
that
the
prevalence
of
negative
side-effects
to
moderate
caffeine
Table
2
Side-effects
reported
by
participants
immediately
after
the
conclusion
of
each
neuromuscular
test
battery
(0
h)
and
24
h
later
(+24
h).
Data
are
presented
as
percent
of
prevalence.
AMPLAC AMCAFF PMPLAC PMCAFF
+0
h
+24
h
+0
h
+24
h
+0
h
+24
h
+0
h
+24
h
Muscle
soreness
15
8
8
31
8
15
15
23
Increased
urine
output
8
8
15
23
8
23
38
38
Tachycardia
and
heart
palpitations
8
0
15
0
15
0
8
0
Anxiety
or
nervousness
8
0
15
0
15
0
0
38
Headache
8
0
8
23
15
8
8
15
Gastrointestinal
problems
0
8
8
8
8
8
8
15
Insomnia
0
8
8
46
Increased
vigor/activeness
8
0
46
8
8
8
54
31
Perception
of
performance
improvement
8
54
8
54
Please
cite
this
article
in
press
as:
Mora-Rodríguez
R,
et
al.
Improvements
on
neuromuscular
performance
with
caffeine
ingestion
depend
on
the
time-of-day.
J
Sci
Med
Sport
(2014),
http://dx.doi.org/10.1016/j.jsams.2014.04.010
ARTICLE IN PRESS
G Model
JSAMS-1024;
No.
of
Pages
5
R.
Mora-Rodríguez
et
al.
/
Journal
of
Science
and
Medicine
in
Sport
xxx
(2014)
xxx–xxx
5
ingestion
(6
mg
kg1)
are
low
in
the
morning
but
higher
in
the
afternoon
(Table
2).
However,
neuromuscular
performance
was
not
improved
by
the
ingestion
of
caffeine
in
the
afternoon.
The
higher
prevalence
of
caffeine
negative
side-effects
in
the
after-
noon
(Table
2),
in
combination
with
the
lack
of
neuromuscular
performance
effects
at
that
time
of
day
(Fig.
1),
suggest
that
the
nutritional-ergogenic
advice
should
focus
on
caffeine
ingestion
prior
to
neuromuscular
exercise
only
in
the
mornings.
Caffeine
is
metabolized
in
the
liver
by
the
P450
enzyme
system
which
is
responsible
for
84%
of
the
primary
degradation
of
caf-
feine
and
leads
to
the
formation
of
paraxanthine,
theobromide
and
to
a
lesser
extent
theophylline.
In
a
study
McLean
and
Graham30
examined
if
exercise,
gender
or
thermal
stress
had
an
influence
on
the
rates
at
which
the
ingested
caffeine
is
degraded.
This
is
an
interesting
question
since
the
pharmacokinetic
of
caffeine
may
be
influenced
by
all
these
factors
and
thus
the
dose
of
caffeine
needed
to
obtain
an
ergogenic
effect
may
be
dependent
on
gender,
ambient
temperature
or
previous
exercise.
In
the
present
study
we
ana-
lyzed
if
time-of-day
influenced
the
concentration
of
these
caffeine
metabolites
in
blood
and
urine.
We
found
that
2
h
after
ingestion
there
was
no
difference
between
the
AMCAFF and
PMCAFF on
caf-
feine
metabolites
in
urine
or
plasma.
This
suggests
that
the
lack
of
effect
of
caffeine
in
the
PM
trials
was
not
due
to
a
different
degra-
dation
rate
or
pharmacokinetic
of
the
ingested
caffeine
than
in
the
AM
trials.
5.
Conclusion
The
main
finding
of
this
study
is
that
caffeine
intake
(6
mg
kg1
body
weight)
enhances
maximal
voluntary
contraction
in
the
mornings
during
full
squat
exercise
against
a
wide
range
of
loads
(25–75%
1RM).
However,
caffeine
ergogenic
effects
in
the
morn-
ing
are
not
statistically
clear
when
resistance
exercise
involves
less
muscle
mass
(i.e.,
bench
press)
(Fig.
1).
Core
temperature
was
not
altered
by
caffeine
ingestion
and
caffeine
was
metabolized
at
sim-
ilar
rates
in
the
AM
and
PM
trials
(Table
1).
Thus,
these
two
factors
(body
temperature
and
caffeine
metabolism)
did
not
seem
to
be
related
to
the
ergogenic
effects
of
caffeine
in
the
mornings.
Finally,
we
observed
a
higher
rate
of
adverse
side-effects
after
ingestion
of
caffeine
in
the
afternoon
in
comparison
to
mornings
(Table
2).
This,
together
with
the
lack
of
performance
effects
in
the
afternoon,
led
us
to
suggest
a
preferential
use
of
caffeine
prior
to
neuromuscular
exercise
in
the
morning.
Practical
implications
The
ingestion
of
a
moderate
dose
of
caffeine
prior
to
exercise
in
the
mornings
(6
mg
kg1)
reverses
the
circadian
related
neuro-
muscular
performance
decrements
found
at
that
time
of
day
in
a
wide
range
of
loads.
Little
effects
of
caffeine
ingestion
should
be
expected
when
performance
is
scheduled
in
the
afternoon,
while
negative
side-
effects
may
appear.
We
discourage
the
use
of
caffeine
in
the
afternoon
to
improve
neuromuscular
performance.
Time-of-day
of
caffeine
ingestion
is
a
confounding
factor
that
may
explain
some
controversy
between
studies
investigating
the
ergogenic
effects
of
caffeine
on
neuromuscular
performance.
Acknowledgements
We
thank
Jesus
Mu˜
noz
and
Gloria
Mu˜
noz
from
the
Spanish
Anti-
doping
Agency
in
Madrid
for
the
analysis
of
caffeine
metabolites.
We
greatly
appreciate
the
commitment
and
dedication
of
each
of
the
13
high
performance
athletes
that
participated
in
this
investi-
gation.
References
1.
Kline
CE,
Durstine
JL,
Davis
JM
et
al.
Circadian
variation
in
swim
performance.
J
Appl
Physiol
2007;
102(2):641–649.
2.
Sedliak
M,
Finni
T,
Peltonen
J
et
al.
Effect
of
time-of-day-specific
strength
training
on
maximum
strength
and
emg
activity
of
the
leg
extensors
in
men.
J
Sports
Sci
2008;
26(10):1005–1014.
3.
Atkinson
G,
Speirs
L.
Diurnal
variation
in
tennis
service.
Percept
Motor
Skills
1998;
86(3
Pt
2):1335–1338.
4.
Jasper
I,
Haussler
A,
Baur
B
et
al.
Circadian
variations
in
the
kinematics
of
hand-
writing
and
grip
strength.
Chronobiol
Int
2009;
26(3):576–594.
5.
Moussay
S,
Bessot
N,
Gauthier
A
et
al.
Diurnal
variations
in
cycling
kinematics.
Chronobiol
Int
2003;
20(5):879–892.
6.
Atkinson
G,
Todd
C,
Reilly
T
et
al.
Diurnal
variation
in
cycling
performance:
influence
of
warm-up.
J
Sports
Sci
2005;
23(3):321–329.
7.
Souissi
N,
Bessot
N,
Chamari
K
et
al.
Effect
of
time
of
day
on
aerobic
contribution
to
the
30-s
wingate
test
performance.
Chronobiol
Int
2007;
24(4):739–748.
8.
Teo
W,
McGuigan
R,
Newton
MJ.
The
effects
of
circadian
rhythmicity
of
salivary
cortisol
and
testosterone
on
maximal
isometric
force,
maximal
dynamic
force,
and
power
output.
J
Strength
Cond
Res
2011;
25(6):1538–1545.
9.
Racinais
S,
Blonc
S,
Jonville
S
et
al.
Time
of
day
influences
the
environ-
mental
effects
on
muscle
force
and
contractility.
Med
Sci
Sports
Exerc
2005;
37(2):256–261.
10.
Souissi
N,
Driss
T,
Chamari
K
et
al.
Diurnal
variation
in
wingate
test
perform-
ances:
Influence
of
active
warm-up.
Chronobiol
Int
2010;
27(3):640–652.
11.
Racinais
S,
Blonc
S,
Hue
O.
Effects
of
active
warm-up
and
diurnal
increase
in
temperature
on
muscular
power.
Med
Sci
Sports
Exerc
2005;
37(12):2134–2139.
12.
Desbrow
B,
Leveritt
M.
Well-trained
endurance
athletes’
knowledge,
insight,
and
experience
of
caffeine
use.
Int
J
Sport
Nutr
Exerc
Metab
2007;
17(4):328–339.
13.
Burke
LM.
Caffeine
sports
performance.
Appl
Physiol
Nutr
Metab
2008;
33(6):1319–1334.
14.
Astorino
TA,
Martin
BJ,
Schachtsiek
L
et
al.
Minimal
effect
of
acute
caffeine
ingestion
on
intense
resistance
training
performance.
J
Strength
Cond
Res
2011;
25(6):1752–1758.
15.
Astorino
TA,
Rohmann
RL,
Firth
K.
Effect
of
caffeine
ingestion
on
one-repetition
maximum
muscular
strength.
Eur
J
Appl
Physiol
2008;
102(2):127–132.
16.
Mora-Rodriguez
R,
Garcia
Pallares
J,
Lopez-Samanes
A
et
al.
Caffeine
ingestion
reverses
the
circadian
rhythm
effects
on
neuromuscular
performance
in
highly
resistance-trained
men.
PLoS
One
2012;
7(4).
17.
Pallares
JG,
Fernandez-Elias
VE,
Ortega
JF
et
al.
Neuromuscular
responses
to
incremental
caffeine
doses:
performance
and
side-effects.
Med
Sci
Sports
Exerc
2013;
45(11):2184–2192.
18.
Souissi
N,
Gauthier
A,
Sesboue
B
et
al.
Circadian
rhythms
in
two
types
of
anaer-
obic
cycle
leg
exercise:
force-velocity
and
30-s
wingate
tests.
Int
J
Sports
Med
2004;
25(1):14–19.
19.
Racinais
S.
Different
effects
of
heat
exposure
upon
exercise
performance
in
the
morning
and
afternoon.
Scand
J
Med
Sci
Sports
2010;
20
Suppl.
3:80–89.
20.
Astorino
TA,
Roberson
DW.
Efficacy
of
acute
caffeine
ingestion
for
short-term
high-intensity
exercise
performance:
a
systematic
review.
J
Strength
Cond
Res
2010;
24(1):257–265.
21.
Shohet
KL,
Landrum
RE.
Caffeine
consumption
questionnaire:
a
standardized
measure
for
caffeine
consumption
in
undergraduate
students.
Psychol
Rep
2001;
89(3):521–526.
22.
Kamimori
GH,
Karyekar
CS,
Otterstetter
R
et
al.
The
rate
of
absorption
and
rela-
tive
bioavailability
of
caffeine
administered
in
chewing
gum
versus
capsules
to
normal
healthy
volunteers.
Int
J
Pharm
2002;
234(1–2):159–167.
23.
Cox
GR,
Desbrow
B,
Montgomery
PG
et
al.
Effect
of
different
protocols
of
caf-
feine
intake
on
metabolism
and
endurance
performance.
J
Appl
Physiol
2002;
93(3):990–999.
24.
Pallares
JG,
Sanchez-Medina
L,
Perez
C
et
al.
Imposing
a
pause
between
the
eccentric
and
concentric
phases
increases
the
reliability
of
isoinertial
strength
assessments.
J
Sports
Sci
2014;
32(12):1165–1175.
25.
Bell
DG,
Jacobs
I,
Ellerington
K.
Effect
of
caffeine
and
ephedrine
ingestion
on
anaerobic
exercise
performance.
Med
Sci
Sports
Exerc
2001;
33(8):1399–1403.
26.
Meyers
BM,
Cafarelli
E.
Caffeine
increases
time
to
fatigue
by
maintaining
force
and
not
by
altering
firing
rates
during
submaximal
isometric
contractions.
J
Appl
Physiol
2005;
99(3):1056–1063.
27.
Warren
GL,
Park
ND,
Maresca
RD
et
al.
Effect
of
caffeine
ingestion
on
mus-
cular
strength
and
endurance:
a
meta-analysis.
Med
Sci
Sports
Exerc
2010;
42(7):1375–1387.
28.
Davis
JM,
Zhao
ZW,
Stock
HS
et
al.
Central
nervous
system
effects
of
caf-
feine
and
adenosine
on
fatigue.
Am
J
Physiol
Regul
Integr
Comp
Physiol
2003;
284(2):R399–R404.
29.
Mohr
T,
Van
Soeren
M,
Graham
TE
et
al.
Caffeine
ingestion
and
metabolic
responses
of
tetraplegic
humans
during
electrical
cycling.
J
Appl
Physiol
1998;
85(3):979–985.
30.
McLean
C,
Graham
TE.
Effects
of
exercise
and
thermal
stress
on
caffeine
pharmacokinetics
in
men
and
eumenorrheic
women.
J
Appl
Physiol
2002;
93(4):1471–1478.