Acute effects of a caffeine-containing supplement on bench press and leg extension strength and time to exhaustion during cycle ergometry


Hendrix, C.Russell.; Housh, T.J.; Mielke, M.; Zuniga, J.M.; Camic, C.L.; Johnson, G.O.; Schmidt, R.J.; Housh, D.J.

Journal of Strength and Conditioning Research 24(3): 859-865

2010


The purpose of the present study was to examine the acute effects of a caffeine-containing supplement (SUPP) on 1 repetition maximum (1RM) bench press and leg extension strength, as well as time to exhaustion (TTE), during cycle ergometry at a power output that corresponded to 80% of VO2peak. The study used a double-blinded, placebo-controlled, crossover design. Twenty-one untrained men (mean +/- SD age = 23.0 +/- 2.6 yr) were randomly assigned to take either the SUPP or placebo (PLAC) first. The SUPP contained 400 mg of caffeine, 66.7 mg of capsicum extract, 10 mg of bioperine, and 40 mg of niacin, and the PLAC was microcrystalline cellulose. Sixty minutes after taking either the SUPP or PLAC, the subjects were tested for 1RM bench press and leg extension strength, as well as TTE. After 1 week of rest, the subjects ingested the opposite substance (SUPP or PLAC) and were retested for 1RM bench press and leg extension strength, as well as TTE. The results indicated that the SUPP had no effect on 1RM bench press strength, 1RM leg extension strength, or TTE at 80% VO2peak. These findings did not support the use of the caffeine-containing SUPP in the present study as an ergogenic aid in untrained individuals.

ACUTE
EFFECTS
OF
A
CAFFEINE-CONTAINING
SUPPLEMENT
ON
BENCH
PRESS
AND
LEG
EXTENSION
STRENGTH
AND
TIME
TO
EXHAUSTION
DURING
CYCLE
ERGOMETRY
C.
RUSSELL
HENDRDE,
1
TERRY
J.
HOUSH,
1
MICHELLE
MIELICE,
1
JORGE
M.
ZUNIGA,
1
CLAYTON
L.
CAMIC,
1
GLEN
0.
JOHNSON,
1
RICHARD
J.
SCHMIDT,
1
AND
DONA
J.
HOUSH
2
'Department
of
Nutrition
and
Health
Sciences,
Human
Performance
Laboratory,
University
of
Nebraska-Lincoln,
Lincoln,
Nebraska;
and
2
Departnzent
of
Oral
Biology,
College
of
Dentistry,
University
of
Nebraska
Medical
Center,
Lincoln,
Nebraska
ABSTRACT
Hendrix,
CR,
Housh,
TJ,
Mielke,
M,
Zuniga,
JM,
Camic,
CL,
Johnson,
GO,
Schmidt,
RJ,
and
Housh,
DJ.
Acute
effects
of
a
caffeine-containing
supplement
on
bench
press
and
leg
exten-
sion
strength
and
time
to
exhaustion
during
cycle
ergometry.
J
Strength
Cond
Res
24(3):
859-865,
2010—The
purpose
of
the
present
study
was
to
examine
the
acute
effects
of
a
caffeine-containing
supplement
(SUPP)
on
1
repetition
maxi-
mum
(1RM)
bench
press
and
leg
extension
strength,
as
well
as
time
to
exhaustion
(TTE),
during
cycle
ergometry
at
a
power
output
that
corresponded
to
80%
of
Vo
2
peak.
The
study
used
a
double-blinded,
placebo-controlled,
crossover
design.
Twenty-
one
untrained
men
(mean
±
SD
age
=
23.0
±
2.6
yr)
were
randomly
assigned
to
take
either
the
SUPP
or
placebo
(PLAC)
first.
The
SUPP
contained
400
mg
of
caffeine,
66.7
mg
of
capsicum
extract,
10
mg
of
bioperine,
and
40
mg
of
niacin,
and
the
PLAC
was
microcrystalline
cellulose.
Sixty
minutes
after
taking
either
the
SUPP
or
PLAC,
the
subjects
were
tested
for
1RM
bench
press
and
leg
extension
strength,
as
well
as
TTE.
After
1
week
of
rest,
the
subjects
ingested
the
opposite
substance
(SUPP
or
PLAC)
and
were
retested
for
1RM
bench
press
and
leg
extension
strength,
as
well
as
TTE.
The
results
indicated
that
the
SUPP
had
no
effect
on
1RM
bench
press
strength,
1RM
leg
extension
strength,
or
TTE
at
80%
Vo
2
peak.
These
findings
did
not
support
the
use
of
the
caffeine-
containing
SUPP
in
the
present
study
as
an
ergogenic
aid
in
untrained
individuals.
KEY
WORDS
endurance
Address
correspondence
to
C.
Russell
Hendrix,
rhendri7@unlserve.unl.
edu
.
24(3)/859-865
Journal
of
Strength
and
Conditioning
Research
©
2010
National
Strength
and
Conditioning
Association
INTRODUCTION
C
affeine
has
become
a
popular
ergogenic
aid
among
recreational
and
competitive
athletes.
The
proposed
benefits
of
caffeine
include
increased
secretion
of
catecholamines
(epinephrine
and
norepinephrine)
(15),
greater
use
of
fats
as
an
energy
source
and
sparing
of
muscle
glycogen
(7),
and
increased
motor
unit
recruitment
and
firing
rates
(17).
Most
studies
have
tested
caffeine's
effects
on
measures
of
endurance
(i.e.,
time
to
exhaustion
[ITE]
at
fixed
power
outputs
or
speeds
during
cycling
or
running
tasks)
(7,13,14,21,26,27)
or
anaerobic
performance
(peak
power
and
mean
power
output
during
Wingate
Anaerobic
Tests,
swimming
velocity
during
100-m
swimming
sprints,
or
time
required
to
complete
a
2000-m
rowing
trial)
(4-6).
Generally
speaking,
these
investigations
have
reported
that
caffeine
improved
performance
during
endurance-based
activities
(7,13,14),
but
the
results
during
anaerobic
activities
have
been
less
consistent
(4,6).
For
example,
Beck
et
al.
(4)
recently
found
that
a
201
mg
dose
of
caffeine
taken
45
minutes
before
exercise
had
no
effect
on
peak
power
or
mean
power
output
during
2
consecutive
Wingate
Anaerobic
Tests
(separated
by
7
min
of
rest)
in
college-age,
resistance-trained
men.
Collomp
et
al.
(6),
how-
ever,
reported
that
a
slightly
higher
dose
of
caffeine
(250
mg)
ingested
1
hour
before
exercise
resulted
in
a
significant
increase
in
average
velocity
for
trained
swimmers
during
2
100-m
sprints
separated
by
20
minutes
of
rest.
Although
the
discrepancies
between
the
results
from
these
studies
(4,6)
may
have
been
caused
by
the
use
of
slightly
different
doses
of
caffeine,
it
is
also
possible
that
they
reflected
differences
in
the
types
of
activities
that
were
performed
(cycling
vs.
swimming).
Another
popular
ergogenic
aid
is
capsaicin
(active
component
of
capsicum
extract),
which
has
been
shown
to
increase
fatty
acid
use
(18,20,31).
Furthermore,
a
combination
of
caffeine
and
capsaicin
has
been
shown
to
increase
energy
expenditure
and
reduce
energy
intake
(30).
In
addition,
bioperine
(black
pepper
extract)
has
been
VOLUME
24
I
NUMBER
3
I
MARCH
2010
I
859
Acute
Effects
of
Caffeine
on
Strength
and
Endurance
reported
to
increase
the
bioavailability
of
other
nutrients
such
as
coenzyme
Q10
and
curcumin
(2,24).
Moreover,
tetrahy-
drobiopterin
(the
active
component
in
bioperine)
is
a
cofactor
to
endothelial
nitric
oxide
synthase
(eNOS),
a
producer
of
nitric
oxide
(a
vasodilator)
and
a
key
moderator
of
vascular
homeostasis
(23,28).
Niacin
is
a
vitamin
that
is
essential
in
energy
metabolism,
and
its
bioavailability
may
be
affected
by
bioperine.
Therefore,
a
combination
of
caffeine,
capsaicin,
bioperine,
and
niacin
may
act
synergistically
to
increase
exercise
performance.
The
mechanisms
by
which
caffeine
enhances
performance
during
aerobic
activities
have
been
examined
in
many
studies,
and
most
investigations
have
suggested
that
caffeine's
ergogenic
effects
on
endurance
are
caused,
in
part,
by
increased
use
offats
as
an
energy
source
and
sparing
ofmuscle
glycogen
(7,12,25).
Very
few
investigations
have
examined
the
mechanism(s)
by
which
caffeine
could
enhance
perfor-
mance
during
maximal
strength
tasks.
Kalmar
and
Cafarelli
(17)
suggested
that
caffeine's
action
as
an
adenosine
receptor
antagonist
could
help
enhance
motor
unit
recruitment
or
firing
rates,
both
of
which
would
contribute
to
increased
force
production.
This
hypothesis,
however,
has
only
been
tested
for
the
leg
extensors
during
a
unilateral
isometric
muscle
action
(17).
Thus,
there
is
very
little
information
regarding
caffeine's
effects
on
strength,
particularly
for
activities
that
are
commonly
performed
by
both
recreational
and
competitive
athletes
(i.e.,
bench
presses,
power
cleans,
squats,
leg
extensions,
etc.).
Therefore,
the
purpose
of
the
present
study
was
to
examine
the
acute
effects
of
a
caffeine-
containing
supplement
(SUPP)
on
1
repetition
maximum
(1RM)
bench
press
and
leg
extension
strength,
as
well
as
TTE,
during
cycle
ergometry
at
a
power
output
that
cor-
responded
to
80%
of
Vo
2
peak.
On
the
basis
of
the
results
of
previous
studies
(4,7,13,14,17),
we
hypothesized
that
the
SUPP
would
result
in
an
increase
in
1RM
bench
press
and
leg
extension
strength,
as
well
as
TTE,
during
cycle
ergometry
at
a
power
output
that
corresponded
to
80%
of
Vo
2
peak.
METHODS
Experimental
Approach
to
the
Problem
This
study
used
a
randomized,
double-blinded,
placebo-
controlled,
within-subjects
crossover
design.
During
the
first
laboratory
visit,
each
subject
performed
an
incremental
test
to
exhaustion
on
an
electronically
braked
cycle
ergometer
to
determine
Vo
2
peak.
After
a
1-week
rest
period,
the
sub-
jects
were
randomly
assigned
to
ingest
either
the
SUPP
or
placebo
(PLAC).
The
SUPP
contained
400
mg
of
caffeine,
66.7
mg
of
capsicum
extract,
10
mg
of
bioperine,
and
40
mg
of
niacin.
The
PLAC
(microcrystalline
cellulose)
was
de-
signed
by
the
manufacturer
(General
Nutrition
Corporation,
Pittsburgh,
PA,
USA)
such
that
each
dose
(2
tablets
=1
dose)
had
the
same
volume,
taste,
and
color
as
the
SUPP.
After
randomization,
the
subjects
ingested
one
dose
of
either
the
SUPP
or
PLAC
and
sat
quietly
in
the
laboratory
for
60
minutes.
The
subjects
were
then
tested
for
1RM
bench
press
860
Journal
of
Strength
and
Conditioning
Researcli
and
leg
extension
strength.
Approximately
15
minutes
after
the
1RM
bench
press
and
leg
extension
strength
tests,
the
subjects
were
tested
for
TTE
on
a
cycle
ergometer
at
a
power
output
that
corresponded
to
80%
of
their
Vo
2
peak.
After
the
TTE
test,
the
subjects
were
allowed
to
rest
for
1
week,
during
which
they
did
not
ingest
either
the
SUPP
or
PLAC.
After
the
1-week
rest
period,
the
subjects
ingested
the
opposite
substance
(SUPP
or
PLAC)
and
were
retested
for
1RM
bench
press
and
leg
extension
strength,
as
well
as
TTE.
Subjects
Twenty-one
men
(mean
±
SD
age
=
23.0
±
2.6
yr;
bodyweight
=
81.0
±
12.1
kg;
height
=
180.2
±
4.8
cm)
volunteered
to
participate
in
the
investigation.
The
subjects
were
untrained
in
both
resistance
and
aerobic
exercise
and
engaged
in
no
more
than
4
hours
of
recreational
activity
per
week.
In
addition,
the
subjects
did
not
report
or
exhibit
(a)
a
history
of
medical
or
surgical
events
that
may
significantly
affect
the
study
outcome,
including
cardiovascular
disease,
metabolic,
renal,
hepatic,
or
musculoskeletal
disorders;
(b)
use
of
any
medication
that
may
significantly
affect
the
study
outcome;
(c)
use
of
nutritional
supplements
(such
as
creatine,
protein
drinks,
amino
acids,
and
vitamins)
in
the
6
weeks
before
the
start
of
the
study;
and
(d)
participation
in
another
clinical
trial
or
ingestion
of
another
investigational
product
within
30
days
before
screening/enrollment.
The
study
was
approved
by
the
University
Institutional
Review
Board
for
Human
Subjects,
and
all
subjects
completed
a
health
history
questionnaire
and
signed
a
written
informed
consent
document
before
testing.
Furthermore,
all
subjects
were
encouraged
to
maintain
their
normal
dietary
habits
and
exercise
routines
during
the
study.
Determination
of
Vo
2
peak
Each
subject
performed
an
incremental
test
to
exhaustion
on
a
Calibrated
Quinton
(Corval
400)
electronically
braked
cycle
ergometer
(Quinton
Instruments,
Inc.,
Seattle,
WA,
USA)
at
a
pedal
cadence
of
70
rev•min
-
l.
Seat
height
was
adjusted
so
that
the
subject's
legs
were
at
near
full
extension
during
each
pedal
revolution.
In
addition,
toe
clips
were
used
to
ensure
that
each
subject
maintained
pedal
contact
throughout
the
ride.
All
subjects
wore
a
nose
clip
and
breathed
through
a
2-way
valve
(2700;
Hans
Rudolph,
Kansas
City,
MO,
USA).
Expired
gas
samples
were
collected
and
analyzed
using
a
calibrated
TrueMax
2400
metabolic
cart
(Parvo
Medics,
Sandy,
UT,
USA)
with
0
2
,
CO
2
,
and
ventilatory
parameters
expressed
as
30-second
averages.
The
metabolic
cart
was
calibrated
before
each
test.
Each
subject
was
fitted
with
a
Polar
Heart
Watch
system
(Polar
Electro,
Inc.,
Lake
Success,
NY,
USA)
to
monitor
heart
rate
throughout
the
test.
The
test
began
at
50
W,
and
the
power
output
was
increased
by
30
W
every
2
minutes
until
voluntary
exhaustion
or
the
subject
could
no
longer
maintain
a
pedal
cadence
of
70
rev•min
-1
despite
strong
verbal
encouragement.
Vo
2
peak
was
the
highest
Vo
l
value
in
the
last
30
seconds
of
the
exercise
test
that
met
at
least
2
of
the
following
3
criteria
(1,8):
(a)
90%
of
Supplement
Placebo
1RM
Leg
Ex
tens
ion
Stre
ng
t
h
(
kg
)
150.00
140.00
130.00
120.00
110.00
100.00
90.00
80.00
70.00
60.00
50.00
40.00
30.00
20.00
10.00
0.00
Supplement
Placebo
1000.00
900.00
S'
800.00
700.00
600.00
500.00
400.00
300.00
200.00
100.00
0.00
Supplement
Placebo
Figure
1.
Top
graph
shows
results
of
1
repetition
maximum
(1
RM)
bench
press
strength
test
for
the
supplement
(SUPP)
and
placebo
(PLAC).
Middle
graph
shows
results
of
1
RM
leg
extension
strength
test
for
SUPP
and
PLAC.
Bottom
graph
shows
results
of
time
to
exhaustion
(TTE)
test
for
SUPP
and
PLAC.
Values
shown
in
all
graphs
are
mean
±
SD.
There
were
no
significant
(p
>
0.05)
mean
differences
for
SUPP
vs.
PLAC
for
1
RM
bench
press
strength,
1
RM
leg
extension
strength,
or
TTE
values.
1RM
Benc
h
Press
Streng
t
h
(
kg
)
120.00
100.00
80.00
60.00
40.00
20.00
0.00
Journal
of
Strength
and
Conditioning
Researdi
I
www.nsca-jscr.org
age-predicted
heart
rate;
(b)
respiratory
exchange
ratio
greater
than
1.1;
and
(c)
a
pla-
teauing
of
oxygen
uptake
(less
than
150
ml•min
-1
in
Vo
l
over
the
last
30
s
of
the
test).
The
test-retest
reliability
data
for
Vo
2
peak
testing
from
our
lab-
oratory
indicated
the
intraclass
correlation
coefficient
(ICC)
was
R
=
0.95,
with
no
signifi-
cant mean
difference
between
test
and
retest
values.
1
RM
Bench
Press
Strength
Test
The
1RM
bench
press
strength
test
was
performed
on
a
stan-
dard
free-weight
bench
(Body
Power,
Williamsburg,
VA,
USA)
with
an
Olympic
bar.
After
receiving
a
lift-off
from
a
spotter,
the
subject
lowered
the
bar
to
his
chest,
paused
briefly,
and
then
pressed
the
bar
to
full
extension
of
the
forearms.
The
1RM
was determined
by
applying
progressively
heavier
loads
until
the
subject
could
not
complete
a
repetition
through
the
full
range
of
motion
(full
extension
of
the
forearms).
Additional
trials
were
perfor-
med
with
addition
of
lighter
loads
until
the
1RM
was
deter-
mined
within
2.27
kg,
and
this
was
usually
achieved
within
5
trials.
Two
minutes
of
rest
were
allowed
between
all
trials
(16).
The
ICC
for
1RM
bench
press
strength
for
our
labora-
tory
is
R=
0.99,
with
no
signifi-
cant mean
difference
between
test
and
retest
values.
1
RM
Leg
Extension
Strength
Test
The
1RM
leg
extension
strength
test
was
performed
on
a
Body-Solid
plate-loaded
leg
extension
machine
(Model
CEC340;
Forest
Park,
IL,
USA).
Each
subject
sat
with
his
torso
against
the
backrest
and
was
instructed
to
hold
tightly
to
the
handles
at
the
sides
of
the
device.
The
backrest
was
adjusted
to
align
the
anatomic
axes
of
the
knees
with
the
mechanical
axis
of
the
machine.
Shin
pads,
attached
to
the
machine's
lever
arm,
were
placed
against
the
subject's
legs.
The
shin
pads
were
a
fixed
distance
from
the
axis
of
rotation
of
the
lever
arm
and
thus
were
not
adjustable.
Positioning,
however,
was
consistent
for
each
subject
across
all
tests.
The
1RM
was
determined
by
applying
progressively
heavier
loads
until
the
subject
could
not
complete
a
repetition
through
the
full
range
of
motion
(full
extension
of
the
legs).
Additional
trials
were
performed
with
lighter
loads
until
the
1RM
was
determined
within
2.27
kg,
and
this
was
usually
achieved
VOLUME
24
I
NUMBER
3
I
MARCH
2010
I
861
Placebo
Supplement
105
100
95
90
85
80
75
70
65
1RM
Benc
h
Press
Streng
t
h
(
kg
)
60
55
160
150
140
4.
9
130
120
,2
110
Lc
100
90
80
70
Placebo
Supplement
Acute
Effects
of
Caffeine
on
Strength
and
Endurance
Time
to
Exhaustion
Test
One
week
after
the
Vo
2
peak
test,
each
subject
performed
a
con-
stant
power
output
ride
on
the
cycle
ergometer
to
determine
TTE.
Each
subject
rode
at
70
rev•min
-1
at
a
power
output
that
corresponded
to
80%
of
the
power
output
at
Vo
2
peak
as
determined
during
the
Vo
2
peak
test.
The
seat
height,
toe
clips,
and
warm-up
procedures
were
the
same
as
for
the
incremental
test.
Each
subject
was
in-
structed
to
ride
until
voluntary
exhaustion,
and
strong
verbal
encouragement
was
provided.
Statistical
Analyses
One
repetition
maximum
bench
press
and
leg
extension
strength,
as
well
as
TTE
values,
were
compared
between
the
SUPP
vs.
PLAC
using
3
sepa-
rate
paired-samples
t-tests.
An
alpha
of
p
0.05
was
consid-
ered
statistically
significant
for
all
comparisons.
An
a
priori
power
analysis
indicated
that,
for
a
repeated
measures
design,
a
sample
size
of
21
subjects
resulted
in
statistical
power
values
of
0.75
or
greater
for
all
of
the
dependent
variables.
1175
1075
975
Time
to
Ex
haus
t
io
n
(s
)
875
775
675
575
475
375
Placebo
within
5
trials.
Two
minutes
of
rest
were
allowed
between
all
trials.
Test-retest
reliability
data
for
1RM
leg
extension
strength
testing
indicated
the
ICC
was
R
=
0.98,
with
no
significant
mean
difference
between
test
and
retest
values.
862
Journal
of
Strength
and
Conditioning
Researcli
RESULTS
Figure
1
shows
the
mean
(±SD)
1RM
bench
press
strength
values
for
the
SUPP
(82.9
±
12.4
kg)
and
PLAC
(82.9
±
12.3
kg).
The
mean
(±SD)
1RM
leg
extension
strength
values
for
the
SUPP
and
PLAC
were
121.7
±
22.4
kg
and
119.2
±
17.6
kg,
re-
spectively
(Figure
1).
The
mean
(±SD)
Fa,
values
for
the
SUPP
and
PLAC
were
6923
±
214.8
s
and
668.5
±
195.7
seconds,
respectively
(Figure
1).
There
were
no
significant
mean
differ-
ences
for
the
SUPP
vs.
PLAC
for
1RM
bench
press
strength,
1RM
leg
extension
strength,
or
TTE
values.
Figure
2
shows
the
individual
1RM
bench
press,
1RM
leg
extension,
and
TTE
values
for
the
PLAC
and
SUPP.
For
the
bench
Supplement
Figure
2.
Top
graph
shows
individual
results
for
1
repetition
maximum
(1
RM)
bench
press
strength
test
for
supplement
(SUPP)
and
placebo
(PLAC).
Middle
graph
shows
individual
results
of
1
RM
leg
extension
strength
test
for
SUPP
and
PLAC.
Bottom
graph
shows
individual
results
of
time
to
exhaustion
(TTE)
test
for
SUPP
and
PLAC.
Journal
of
Strength
and
Conditioning
Researdi
I
www.nsca-jscr.org
press,
6
subjects
had
greater
1RM
values
for
the
SUPP
than
the
PLAC,
3
subjects
had
greater
values
for
the
PLAC
than
the
SUPP,
and
for
12
subjects
the
1RM
values
were
the
same
for
the
SUPP
and
PLAC.
For
leg
extension,
12
subjects
had
greater
1RM
values
for
the
SUPP
than
the
PLAC,
5
subjects
had
greater
values
for
the
PLAC
than
the
SUPP,
and
for
7
subjects
the
1RM
values
were
the
same
for
the
SUPP
and
PLAC.
For
fn,,
11
subjects
had
greater
TTE
values
for
the
SUPP
than
the
PLAC,
whereas
10
subjects
had
greater
TTE
values
for
the
PLAC
than
the
SUPP.
DISCUSSION
The
results
of
this
investigation
showed
that
the
SUPP
containing
400
mg
of
caffeine
(approximately
4.9
mg•kg
-1
of
bodyweight)
had
no
effect
on
mean
1RM
bench
press
or
leg
extension
strength.
There
were,
however,
individual
differ-
ences
in
responses
for
1RM
bench
press
and
leg
extension
strength.
For
1RM
bench
press
strength,
28.6%
of
the
subjects
had
greater
1RM
values
(2.3
kg)
for
the
SUPP,
14.3%
of
the
subjects
had
greater
1RM
values
(range
=
2.3-6.8
kg)
for
the
PLAC,
and
57.1%
of
the
subjects'
1RM
values
were
the
same
for
the
SUPP
and
PLAC.
The
SUPP
resulted
in
greater
1RM
leg
extension
values
(range
=
2.3-18.1
kg)
for
57.1%
of
the
subjects,
the
PLAC
resulted
in
greater
1RM
leg
extension
values
(range
=
9.1-18.1
kg)
for
23.8%
of
the
subjects,
and
33.3%
of
the
subjects'
1RM
leg
extension
values
were
the
same
for
the
SUPP
and
PLAC.
Recent
studies
(3,4,6,12,13,17)
have
suggested
that
the
conflicting
evidence
regarding
the
effect
of
caffeine
on
muscular
performance
may
be
caused
by
the
training
status
of
the
subjects,
doses
used,
type
of
muscle
action
performed
(isometric
vs.
dynamic),
or
the
muscle
group
tested.
For
example,
Kalmar
and
Cafarelli
(17)
reported
that
a
6
mg•kg
-1
of
bodyweight
dose
(mean
±
SD
=
428
54
mg)
of
caffeine
significantly
increased maximal
voluntary
unilateral,
isometric
leg
extension
strength
by
a
mean
of
approximately
5.8
±
3%.
Beck
et
al.
(4)
reported
that
a
201
mg
dose
of
caffeine
resulted
in
a
significant
increase
(2.1
kg
=
2.1%)
in
1RM
bench
press
but
not
leg
extension
strength
in
resistance
trained
subjects
(regularly
participating
in
at
least
4
resistance
training
sessions
per
week).
The
same
201
mg
dose
of
caffeine,
however,
had
no
effect
on
1RM
bench
press
strength
in
untrained
subjects
(3).
Thus,
the
findings
of
Beck
et
al.
(3),
as
well
as
the
present
study,
indicated
that,
in
untrained
subjects,
201
and
400
mg
of
caffeine
had
no
effect
on
1RM
bench
press
or
leg
extension
strength.
In
resistance
trained
subjects,
however,
doses
of
caffeine
as
low
as
201
mg
increased
1RM
strength
for
upper-body
(bench
press),
but
not
lower-body
(leg
extension),
exercises
(4).
The
specific
mechanism
by
which
caffeine
affects
perfor-
mance
during
maximal
strength
activities
is
unknown.
Kalmar
and
Cafarelli
(17)
reported
that
caffeine
(6
mg•kg
-1
of
body-
weight
ingested
1
hr
before
exercise)
resulted
in
significant
increases
in
both
isometric
leg
extension
strength
(approxi-
mately
a
5.8%
increase)
and
maximal
voluntary
muscle
activation
(approximately
a
3%
increase)
during
a
unilateral
isometric
maximum
voluntary
contraction
of
the
leg
exten-
sors.
It
was
hypothesized
(17)
that
caffeine,
which
is
similar
in
structure
to
adenosine,
may
have
acted
as
an
antagonist
to
adenosine
receptors
of
the
central
nervous
system
(CNS).
Specifically,
adenosine
binding
to
its
receptor
in
the
CNS
inhibits
neurotransmitter
release
and
decreases
neuronal
firing
rates,
both
of
which
can
result
in
reduced
muscle
activation
and
force
production
(17).
Binding
of
caffeine
with
adenosine
receptors
in
the
CNS
could
increase
maximal
voluntary
activation
and
force
production
(i.e.,
because
of
competitive
inhibition
of
adenosine)
by
allowing
for
greater
motor
unit
recruitment
or
firing
rates
(17).
The
results
from
the
present
study,
in
conjunction
with
previous
studies
(3,4),
however,
indicated
that
caffeine
supplementation
may
pro-
duce
different
results
with
regard
to
the
expression
of
maximal
strength
in
trained
vs.
untrained
subjects.
Additional
research
is
needed
to
investigate
the
acute
effects
of
various
doses
of
caffeine
on
muscular
strength
during
a
variety
of
exercise
activities.
In
addition,
on
the
basis
of
the
findings
of
Beck
et
al.
(3,4),
as
well
as
the
current
study,
future
studies
should
examine
the
acute
effects
of
caffeine
on
maximal
strength
for
upper-
and
lower-body
movements
in
trained
vs.
untrained
subjects.
The
results
from
this
investigation
also
showed
that
the
400
mg
caffeine
SUPP
(approximately
4.9
mg•kg
-1
of
body-
weight)
had
no
effect
on
TTE
(mean
=
11.4
and
11.2
min
for
SUPP
and
PLAC,
respectively)
(Figure
1)
during
cycle
ergometry
at
80%
Vo
2
peak.
There
were,
however,
individual
differences
for
TTE.
That
is,
the
TTE
values
(range
=
8-702
s)
for
52.4%
of
the
subjects
were
greater
for
the
SUPP,
whereas
47.6%
of
the
subjects'
rn,
values
(range
=
4-402
s)
were
greater
for
the
PLAC.
These
findings
were
consistent
with
those
of
Beck
et
al.
(3),
who
reported
that
a
201
mg
dose
of
caffeine
had
no
effect
on
TTE
at
85%
Vo
2
peak
during
treadmill
running.
These
findings,
however,
were
not
con-
sistent
with
previous
studies
that
reported
caffeine
improved
endurance
performance
(i.e.,
TTE)
during
activities
that
lasted
30
to
60
minutes
(7,15,21,25-27).
The
primary
hy-
potheses
regarding
increased
TTE
during
aerobic
activities
(7,11,12,25,27)
were
increased
use
of
fatty
acids
and
a
glycogen
sparing
effect.
For
example,
Essig
et
al.
(11)
examined
the
effects
of
caffeine
(5
mg•kg
-1
of
bodyweight
ingested
60
min
before
exercise)
on
substrate
use
(assessed
by
way
of
respiratory
exchange
ratio)
during
30
minutes
of
cycle
ergometry
at
65-75%
Vo
2
peak
and
reported
that
fatty
acid
use
was
significantly
higher
and
carbohydrate
use
was
significantly
lower
for
caffeine
supplementation
compared
with
placebo.
Furthermore,
Greer
et
al.
(15)
examined
the
effects
of
caffeine
(6
mg•kg
-1
of
bodyweight
ingested
90
min
before
exercise)
on
muscle
glycogen
content
(assessed
by
way
of
muscle
biopsies)
during
a
45-minute
cycle
ergometer
workbout
at
65-70%
Vo
2
peak
and
reported
that
muscle
glycogen
decreased
at
similar
rates
for
caffeine
supplemen-
tation
and
a
dextrose
placebo.
Thus,
it
was
suggested
that,
during
aerobic
exercise,
caffeine
may
promote
increased
use
VOLUME
24
I
NUMBER
3
I
MARCH
2010
1
863
Acute
Effects
of
Caffeine
on
Strength
and
Endurance
of
fatty
acids
but
may
not
decrease
the
rate
of
muscle
glycogen
use
(15).
It
should
be
noted
that
the
key
component
determining
performance
during
the
TTE
workbouts
in
the
present
study
may
not
have
been
muscle
glycogen
stores.
Although
muscle
glycogen
and
blood
lactate
were
not
measured
in
this
inves-
tigation,
it
is
possible
that
TTE
at
80%
Vo
2
peak
was
in-
fluenced
more
by
the
accumulation
of
metabolites
(i.e.,
lactate,
inorganic
phosphate,
ammonia)
than
depletion
of
glycogen.
This
hypothesis
is
supported
by
the
results
from
cycle
ergometry
studies
that
have
examined
the
acute
effects
of
caffeine
on
performance
during
exercise
tasks
that
elicit
fatigue
within
10
to
20
minutes
(9,22).
For
example,
Powers
et
al.
(22)
reported
that,
during
an
incremental
cycle
ergo-
meter
test
(beginning
workload
of
30
W,
with
30
W
increases
every
3
min
until
exhaustion),
caffeine
supplementation
(5
mg•kg
-1
of
bodyweight
ingested
1
hr
before
exercise)
had
no
effect
on
TTE
or
the
time
course
of
blood
lactate
accumu-
lation.
Dodd
et
al.
(9)
used
an
incremental
cycle
ergometry
exercise
protocol
identical
to
the
present
study
(a
beginning
workload
of
50
W,
with
30
W
increases
every
2
min
until
exhaustion)
and
reported
that
2
different
caffeine
doses
(3
or
5
mg•kg
-1
of
bodyweight)
resulted
in
a
significant
increase
in
plasma-free
fatty
acid
concentration
but
had
no
effect
on
the
lactate
threshold
or
TTE.
Thus,
the
findings
of
the
present
study,
in
conjunction
with
those
of
Powers
et
al.
(22)
and
Dodd
et
al.
(9),
indicated
that
caffeine
did
not
affect
TTE
during
activities
designed
to
elicit
fatigue
within
10
to
20
minutes.
Future
studies
should
test
this
hypothesis
with
various
caffeine
doses
during
both
cycling
and
running
activities.
In
addition
to
caffeine,
the
SUPP
also
contained
capsicum
extract
(active
component
is
capsaicin),
bioperine
(black
pepper
extract),
and
niacin.
Capsicum
is
a
genus
of
plants
including
various
peppers
(i.e.,
chili,
jalapeno,
habanero),
which
contain
capsaicin.
Previous
studies
(10,18,20,29-31)
have
suggested
that
intake
of
thermogenic
ingredients
(i.e.,
caffeine,
capsaicin,
and
black
pepper)
have
the
potential
to
increase
fatty
acid
or
carbohydrate
use.
Furthermore,
Lim
et
al.
(19)
reported
that
respiratory
quotient
and
blood
lactate
levels
of
trained
runners,
both
at
rest
and
during
exercise,
increased
after
ingesting
a
meal
containing
10
g
of
hot
red
pepper
(2.5
hr
before
cycling
at
60%
Vo
2
peak).
The
authors
(19)
also
reported
increased
catecholamine
levels
(epineph-
rine
and
norepinephrine)
30
minutes
after
ingestion
and
suggested
that
hot
red
peppers
stimulated
carbohydrate
oxidation
both
at
rest
and
during
exercise.
Bioperine
(piperine)
is
a
standardized
extract
from
the
fruits
of
Piper
nigrum
(black
pepper)
and
has
been
reported
to
increase
the
absorption
and
bioavailability
of
other
nutrients
(2,24).
Specifically,
Badmaev
et
al.
(2)
reported
that
5
mg
of
piperine
co-administered
with
120
mg
coenzyme
Q10
for
21
days
significantly
increased
plasma
levels
of
coenzyme
Q10
when
compared
with
a
control
group
(120
mg
of
coenzyme
Q10
with
placebo).
Furthermore,
Shoba
et
al.
(24)
reported
that
20
mg
of
piperine
plus
2
g
of
curcumin
significantly
increased
864
Journal
of
Strength
and
Conditioning
Researcli
blood
serum
levels
of
curcumin
compared
with
administra-
tion
of
curcumin
alone
(2
g
of
curcumin
in
capsules
identical
to
combined
piperine
and
curcumin
capsules).
Furthermore,
the
active
component
in
bioperine,
tetrahydrobiopterin
(BH4),
is
a
cofactor
to
eNOS,
a
producer
of
nitric
oxide
(a
vasodilator)
and
a
key
moderator
of
vascular
homeostasis
(23,28).
Thus,
theoretically,
capsicum
extract
and
bioperine
may
act
synergistically
with
caffeine
to
increase
substrate
oxidation.
Future
studies
should
examine
the
possible
synergistic
effects
of
caffeine,
capsaicin,
and
black
pepper
extract
to
determine
their
metabolic
effects
during
both
exercise
and
rest
(pre-
and
postexercise).
In
summary,
the
results
from
this
study
showed
that
the
SUPP
containing
caffeine,
capsicum
extract,
bioperine,
and
niacin
had
no
effect
on
1RM
strength
(bench
press
or
leg
extension)
or
TTE
at
80%
Vo
2
peak.
It
is
possible
that
these
findings
were
influenced
by
the
training
status
of
the
subjects
(untrained)
or
the
relative
intensity
of
the
exercise
task.
Future
studies
should
examine
these
issues
in
addition
to
testing
the
acute
effects
of
various
doses
of
caffeine
on
per-
formance
during
strength,
power,
and
endurance
activities.
PRACTICAL
APPLICATIONS
The
results
from
this
study
indicated
that
ingestion
of
a
SUPP
that
contained
caffeine,
capsicum
extract,
bioperine,
and
niacin
had
no
effect
on
upper-
and
lower-body
strength
or
endurance
cycling
performance
in
untrained
men.
Thus,
these
findings
did
not
support
the
use
of
caffeine,
at
the
dosage
examined
in
the
present
investigation,
as
an
ergogenic
aid
for
untrained
individuals.
The
results
from
previous
studies,
however,
demonstrated
that
the
acute
effects
of
caffeine
on
upper-body
strength
(4)
and
sprint
swimming
performance
(6)
may
be
greater
for
trained
than
untrained
individuals.
Therefore,
additional
research
is
needed
to
determine
if
the
acute
effects
of
various
doses
of
caffeine
are
influenced
by
training
status.
ACKNOWLEDGMENTS
This
study
was
funded
by
a
research
grant
from
General
Nutrition
Corporation.
The
results
of
the
present
study
do
not
constitute
endorsement
of
the
product
by
the
authors
or
the
NSCA.
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