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Background: We examined the effects of ingesting two preworkout supplements (PWSs) on selective attention and response inhibition, perceived exercise readiness (herein, readiness), and exercise performance-related parameters. Methods: Resistance-trained participants (N = 19) were randomized to a double-blind, crossover (7-day washout) placebo (PLA)-controlled study supplementing with (1) PLA; (2) PWS [beta-alanine (3.2 g), arginine alpha ketoglutarate (2.0 g), creatine nitrate (2.0 g), ascorbic acid (500 mg), N-acetyl tyrosine (300 mg), caffeine (300 mg), tetramethyluric acid (10 mg), Mucuna pruriens extract standardized for 15% l-Dopa (1.0 g), theacrine (10 mg), pyridoxal 5-phosphate (1.48 mg), folic acid (0.50 mg), and methylcobalamin (1.8 mg)]; and (3) PWS150 at ∼150% the PWS dose. Primary outcomes were Stroop test responses for congruent, incongruent, and interference tasks. Secondary outcomes were readiness and exercise performance (bench and leg press/Wingate). Data were analyzed by general linear models and presented as mean (standard deviation) or mean change [95% confidence interval, CI]. Results: Significant improvements in Stroop word testing were observed for PWS (6.57, 95% CI [1.36–11.8]) and PWS150 (11.5, 95% CI [6.26–16.6]), but not PLA (1.31, 95% CI [−3.89 to 6.52]). Significant changes in Stroop color testing were observed for PWS150 (8.1, 95% CI [4.52–11.6]) and PLA (4.47, 95% CI [0.89–8.05]), but not PWS (2.31, 95% CI [−1.26 to 5.89]). Similar results were observed for word–color. When all domains were summed, PWS150 (27.42 counts, 95% CI [16.08–38.76]) and PWS (12.26 counts, 95% CI [0.92–23.60]) showed significant improvements, but not PLA (11.26 counts, 95% CI [−0.077 to 22.60]). No significant changes in readiness, exercise performance, or adverse changes were otherwise observed. Conclusion: Consistent improvements in selective attention and response inhibition were observed with PWS150, but not readiness or exercise performance.
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Original Article
Dose Response to One Week of Supplementation
of a Multi-Ingredient Preworkout Supplement
Containing Caffeine Before Exercise
Majid S. Koozehchian, PhD,
Conrad P. Earnest, PhD,
Y. Peter Jung, PhD,
P. Blaise Collins, MS,
Abigail O’Connor, MS,
Ryan Dalton, MS,
Song Yi Shin, MS,
Ryan Sowinski, MS,
Chris Rasmussen, MS,
Peter S. Murano, PhD,
Mike Greenwood, PhD,
and Richard B. Kreider, PhD
Background: We examined the effects of ingesting two preworkout supplements (PWSs) on selective at-
tention and response inhibition, perceived exercise readiness (herein, readiness), and exercise performance-
related parameters.
Methods: Resistance-trained participants (N=19) were randomized to a double-blind, crossover (7-day
washout) placebo (PLA)-controlled study supplementing with (1) PLA; (2) PWS [beta-alanine (3.2 g), ar-
ginine alpha ketoglutarate (2.0 g), creatine nitrate (2.0 g), ascorbic acid (500 mg), N-acetyl tyrosine
(300 mg), caffeine (300 mg), tetramethyluric acid (10 mg), Mucuna pruriens extract standardized for
15% l-Dopa (1.0 g), theacrine (10 mg), pyridoxal 5-phosphate (1.48 mg), folic acid (0.50 mg), and
methylcobalamin (1.8 mg)]; and (3) PWS150 at *150% the PWS dose. Primary outcomes were Stroop
test responses for congruent, incongruent, and interference tasks. Secondary outcomes were readiness
and exercise performance (bench and leg press/Wingate). Data were analyzed by general linear models
and presented as mean (standard deviation) or mean change [95% confidence interval, CI].
Results: Significant improvements in Stroop word testing were observed for PWS (6.57, 95% CI [1.36–
11.8]) and PWS150 (11.5, 95% CI [6.26–16.6]), but not PLA (1.31, 95% CI [3.89 to 6.52]). Significant
changes in Stroop color testing were observed for PWS150 (8.1, 95% CI [4.52–11.6]) and PLA (4.47,
95% CI [0.89–8.05]), but not PWS (2.31, 95% CI [1.26 to 5.89]). Similar results were observed for
word–color. When all domains were summed, PWS150 (27.42 counts, 95% CI [16.08–38.76]) and PWS
(12.26 counts, 95% CI [0.92–23.60]) showed significant improvements, but not PLA (11.26 counts, 95%
CI [0.077 to 22.60]). No significant changes in readiness, exercise performance, or adverse changes
were otherwise observed.
Conclusion: Consistent improvements in selective attention and response inhibition were observed with
PWS150, but not readiness or exercise performance.
Keywords: ergogenic aids, dietary supplement, exercise performance, safety, cognitive function
Apopular strategy for improving exercise perfor-
mance is to ingest preworkout supplements (PWSs).
While several singular nutrient strategies exist in the lit-
erature (i.e., caffeine, carbohydrate, carbohydrate mouth
rinsing, and beetroot ingestion), less is known about multi-
ingredient supplements that exist in the marketplace.
The investigation of such products is important as PWS
formulae vary widely regarding ingredients, yet are seldom
tested for efficacy. Such investigations are also important
as ingredient combinations may act synergistically or in
Exercise and Sport Nutrition Laboratory, Department of Health and Kinesiology, Texas A&M University, College Station, Texas.
Nutrabolt, Bryan, Texas.
Department of Nutrition and Food Sciences, Institute for Obesity Research and Program Evaluation, Texas A&M University,
College Station, Texas.
Volume 7, Number 2, 2017
ªMary Ann Liebert, Inc.
DOI: 10.1089/jcr.2017.0001
opposition relative to the formula ingredients. The cur-
rent study examines the effectiveness of ingesting a PWS
comprising (i) beta-alanine, arginine alpha ketoglutarate
(AKG), creatine nitrate, ascorbic acid, N-acetyl tyrosine,
caffeine, tetramethyluric acid, Mucuna pruriens extract stan-
dardized for 15% l-Dopa, theacrine, pyridoxal 5-phosphate,
folic acid, and methylcobalamin or (ii) the same formula de-
livered at *150% of each ingredient (PWS150, dosing out-
lined below).
Numerous reviews and meta-analyses are available in
the literature attesting to the performance-enhancing ef-
fects of creatine monhydrate,
and beta-alanine.
Less is known regarding creatine
nitrate, and the literature to date suggests possible sup-
plementation effects. Despite an increase in Stroop test-
ing and self-reported readiness to perform exercise, the
performance-enhancing effects of creatine nitrate are
minimal, although they appear free of side effects as
reported in each study.
Although not as robust in
the literature, arginine alpha-ketoglutarate has been
shown to increase one repetition maximum (1RM) in
the bench press and Wingate peak power performance
and bench press repetitions over three sets of exercise, as
well as Wingate peak and average power when combined
with creatine monohydrate.
Mucuna pruriens is a naturally occurring nonprotein
amino acid that is shown to significantly improve passive
avoidance acquisition and memory retrieval compared
with the controls in rats and in one human study.
The physiological basis of tyrosine’s beneficial effects
on cognitive function is attributed to its role as a precur-
sor for catecholamine neurotransmitters, dopamine, and
norepinephrine. In addition, tyrosine has the potential,
as an acute treatment, to prevent stress-related decline
in cognitive function,
while tetramethyluric acid has
been shown to increase excitability and locomotor activity
in rats similar to caffeine.
Studies in humans have shown
an increase in subjective feelings of energy and mood
and concentration
without undesirable perturbations in
clinical markers such as heart rate, blood pressure, lipid
profiles, hematologic blood counts, and biomarkers
of liver/kidney/immune function.
Finally, human stud-
ies using up to 250 mg/day have shown pterostilbene to
decrease blood pressure and body weight
and poten-
tially enhance glycogen replenishment through enhanced
insulin sensitivity by enhancing hepatic enzymes associ-
ated with glucose uptake.
The primary aim of the current study was to examine a
PWS administered in two different doses over a 7-day
period. The primary outcome is cognitive function as de-
termined by Stroop test. Overall, the Stroop test exam-
ines ones cognitive ability to direct attention to a task
through attention and response inhibition using word–
color testing. In brief, a number of studies have used
the Stroop test concurrent to exercise or caffeine inges-
tion relative to executive function and cognitive flexibil-
preadolescent performance in children relative to
aerobic fitness,
upright versus recumbent cycling,
caffeine ingestion,
mental fatigue in professional cy-
and after maximal cycle ergometry in elite sports-
Secondary outcomes include participants’ readiness
to perform exercise, exercise performance, resting metabo-
lism, resting and postexercise hemodynamics, exercise per-
formance, and standardized blood chemistries assessing
hepatorenal and muscle enzyme functions. We hypothesize
that individuals ingesting a PWS will (i) improve Stroop
testing; (ii) exhibit a heightened state of readiness; and
(iii) increase exercise performance following 7 days of sup-
The current study was conducted at the Exercise and
Sport Nutrition Laboratory (ESNL) of Texas A&M Uni-
versity after obtaining approval from the university eth-
ics committee. A Consolidated Standards of Reporting
Trials diagram of our study is presented in Figure 1
and a study procedural outline is presented in Figure 2.
The following methods are divided into two sections pro-
viding (i) a study overview followed by (ii) a detailed
presentation of analysis methods used to assess our pro-
posed outcomes.
Study Overview
Recruitment and familiarization. Participants were re-
cruited for the study through the use of e-mail invitations
and flyers posted on the university campus. Before for-
mally starting the study, participants attended a familiar-
ization session to sign informed consent, complete a
health history questionnaire that was reviewed by a reg-
istered nurse, review the study protocol both verbally
and in writing, and practice the various testing proto-
cols. Qualifying participants were assessed for standard
anthropometric measurements, including height, weight,
heart rate, and blood pressure, and dual-energy x-ray
absorptiometry (DXA) was determined body composi-
tion. Before the DXA measurements, female participants
completed and signed the radiation exposure question-
naire for women of childbearing age. After completing
the DXA, participants performed a 1RM test on the
bench press and leg press and a Wingate 30-second an-
aerobic capacity test on a cycle ergometer. Each test
was interspersed with a 5-minute rest period. All testing
was performed on the same day so as to better emulate
the demands of workout versus testing on separate
days, which we felt would minimize the purported pre-
workout benefits of ingesting such a supplement routine.
Following the successful completion of the familiariza-
tion visit, eligible participants were then scheduled for
baseline testing. Participants were then randomly
assigned to initiate testing in a blinded and counterbal-
anced manner regarding treatment.
Eligibility. Participants were eligible to participate in
our study if they presented with 6 months and current his-
tory of resistance training inclusive of performing bench
and leg press or squat. Participants were excluded from
the study if they were under 18 years or above 40
years; had a history of treatment for metabolic disease
(e.g., diabetes), hypertension, hypotension, thyroid dis-
ease, arrhythmia, and/or cardiovascular disease; current
use of any prescription medication; intolerance to caf-
feine and/or other natural stimulants; pregnant or lactat-
ing women; a history of smoking; or excessive drinking
(>12 drinks/week). Additional exclusion criteria included
caffeine intolerance and/or natural stimulants. During the
study, participants were asked to continue their current
training program without initiating any new exercise or
diet regime.
Performance testing. Baseline and follow-up testing
took place after a 12-hour fast with participants hav-
ing refrained from exercise training, the ingestion of
FIG. 1. Consolidated Standards of Reporting Trials diagram of study.
FIG. 2. Schematic representation of the study procedures.
caffeine, and/or over-the-counter medications/supple-
ments with known stimulant use for 48 hours. Once at
the laboratory, participants donated *20 mL of blood
through venipuncture. Participants were then weighed
and assessed for resting heart rate and blood pressure,
electrocardiography, and resting energy expenditure
(REE). Resting metabolism was measured in the supine
position for 60 total minutes. During the first 30 minutes,
the participants were unsupplemented, whereby partici-
pants then ingested their respective treatments and
were examined again for another 30 minutes. After com-
pleting the REE, each participant performed the Stroop
word–color test to assess cognitive function as well as as-
sess their self-assessed perception of readiness, sleep
quality, and sensations of stimulation through a stimulant
questionnaire. Participants were then measured for total
body water through bioelectrical impedance analysis,
warmed up for 5 minutes, and then performed exercises
examining strength (leg and bench press), followed by
a Wingate Anaerobic Power Test, which were inter-
spersed by 5 minutes of rest between each trial. Follow-
ing each assessment, heart rate and blood pressure were
measured within 1 minute of the completion of each exer-
cise. These latter tests were undertaken to examine whether
each treatment affected postexercise hemodynamics.
Testing methodology
Treatments. Treatments for this study consisted of
(1) dextrose-flavored placebo (PLA) (12 g of glucose);
(2) PWS (12 g/day) mixed into *235 mL of plain
water consisting of beta-alanine (3.2 g), arginine AKG
(2.0 g), creatine nitrate (2.0 g), ascorbic acid (500 mg),
N-acetyl tyrosine (300 mg), caffeine (300 mg), tetrame-
thyluric acid (10 mg), Mucuna pruriens extract standard-
ized for 15% l-Dopa (1.0 g), theacrine (10 mg), pyridoxal
5-phosphate (1.48 mg), folic acid (0.50 mg), and methylco-
balamin (1.8 mg) plus 2.6 g dextrose; and (3) PWS at 150%
dosage (PWS150) of PWS.
Supplements were prepared in coded single-foil pack-
ets and labeled for double-blind administration. Both
supplements and the PLA were similar in flavor and ap-
pearance. During the supplementation week, except for
baseline and follow-up sessions, participants ingested
their assigned supplement in two forms: on workout
days, they ingested their supplement about 30 minutes be-
fore their workout; and on nonworkout days, they ingested
that around noon. Participants repeated the experiment
after a 7-daywashout period with the alternate supplements
in a randomized manner.
Anthropometry. Body mass and height were mea-
sured by a Healthometer Professional 500KL (Pelstar,
LLC, Alsip, IL) self-calibrating digital scale with an ac-
curacy of 0.02 kg. Whole body composition measures
(excluding cranium) were determined by a Hologic Dis-
covery W DXA (excluding cranium; Hologic, Inc.,Wal-
tham, MA) equipped with APEX Software based on
procedures previously described.
Diet. During baseline and follow-up, participants
were asked to precisely record all the food items (brand
if applicable), preparation method, and total quantity con-
sumed, as well as beverage consumption except water.
The next two dietary recordings then took place during
the washout period before each supplementation week.
All food logs were entered and analyzed by a registered
dietitian using dietary analysis software (ESHA Food Pro-
cessor, Version 8.6; ESHA Research, Salem, OR).
Hemodynamic assessment. Heart rate was obtained
from a resting CARDIO System 12-lead ECG (Nasiff Asso-
ciates, Inc., Brewerton, NY) and through pulse palpation of
the radial artery.
Blood pressure was measured by aus-
cultation of the brachial artery using a mercurial sphyg-
momanometer using a standard clinical procedure.
REE measurement. REE was measured by indirect
calorimetry using a metabolic cart (Parvo Medics True-
Max 2400 Metabolic Measurement System ParvoMed-
ics, Inc., Sandy, UT). A plastic hood was placed over
the participant’s head, preventing external air from en-
tering the hood, and REE was collected in the supine
position for 30 minutes before and 30 minutes after sup-
plement ingestion and recorded as the average of the last
5 minutes of the collection period.
Stroop Word–Color test. We examined the effective-
ness of using a PWS on attention, interference, and cog-
nition through use of the Stroop word–color test.
The test consists of a word page with colored words
printed in black ink, a color page with Xs printed in
color, and a color–word page with words from the first
page printed in colors from the second page where the
color and the word do not match). Participants worked
through each sheet as quickly as possible within a time
limit. The first two tests measure congruence, while the
last test examines incongruence or interference to identify
the appropriate word independent of color. The number
of correct responses obtained during the time period is
used to assess cognitive function. Day-to-day test reliabil-
ity of administering this test in our laboratory has yielded
coefficients of variation ranging from 0.14 to 0.25 counts
and intraclass correlation coefficients of 0.90, 0.68, and
0.57 for word, color, and word–color, respectively. Jen-
sen reported test/retest reliabilities of 0.88, 0.79, and 0.71
for the three word, color, and word–color raw scores.
Golden reported test/retest reliabilities of 0.86, 0.82,
and 0.73 for the individual version.
All tests were ana-
lyzed as single domains as well as summed for a total
score of all three domains.
Readiness to perform exercise. Readiness to perform
exercise, herein readiness, was measured by a visual
analog scale by having participants assess six questions
reporting their subjective feelings ranging from strongly
disagree to strongly agree on 20 cm dotted bar as (1) ‘‘I
slept well last night,’’ (2) ‘‘I am looking forward to to-
day’s workout,’’ (3) ‘‘I am optimistic about my future
performance,’’ (4) ‘‘I feel vigorous and energetic,’’ (5)
‘‘My appetite is great,’’ and (6) ‘‘I have little muscle
soreness.’’ Participants circled the number or dots between
numbers that best indicated how they currently felt. Day-
to-day test reliability in our laboratory is 2–4%, coefficient
variation (CV) ranging from 0.19 to 0.34, and intraclass
correlation coefficients of 0.83, 0.86, 0.89, and 0.34 for
questions 1 through 4, respectively.
Strength and Wingate anaerobic capacity testing. Max-
imal strength was determined following a standard
warm-up consisting of ten repetitions using 50% (set
1), then five repetitions using 70% (set 2), and one repe-
tition using 90% (set 3) of their estimated 1RM. Partici-
pants continued increasing weight until their 1RMs were
determined. Participants were encouraged to reach 1RM
during the familiarization trials. With 1RM that was de-
termined at the familiarization session, participants per-
formed three sets of bench and leg press tests. At the
first and second sets, participants were required to lift
10 repetitions at 70% of 1RM on the bench press and
leg press, interspersed by 2 minutes of rest between
sets, and 5-minute recovery between each exercise test-
ing modality. During the third set, we asked participants
to complete as many repetitions as possible. Total lifting
volume was calculated by multiplying the amount of
weight lifted times the number of successful repetitions
completed. The concurrent verbal encouragement was
applied during the tests as an extrinsic motivational
factor to encourage maximal performance. All strength
testing took place on an isotonic Olympic bench press
and hip/leg sled (Nebula Fitness, Versailles, OH) using
standard procedures.
Day-to-day test reliability of
performing this endurance test in our laboratory on
resistance-trained participants has yielded a CV of
0.34, an intraclass correlation coefficient of 0.99 for
three sets of bench press total lifting volume, and a
CV of 0.32 and an intraclass correlation coefficient of
0.96 for three sets of leg press total lifting volume.
The Wingate test requires the participant to pedal a
mechanically braked bicycle ergometer for 30 seconds
at an all-out pace. Wingate testing was assessed using a
Lode Excalibur Sport Ergometer (Lode BV, Groningen,
The Netherlands) and work rate was set at of 7.5 J/kg/rev
for everyone. Participants were asked to pedal as fast as
possible for 10 seconds before application of the workload
and sprint at an all-out maximal capacity for 30 seconds.
Concurrent verbal encouragement was applied during
the test as an extrinsic motivational factor to encourage
maximal performance. Day-to-day variability in perform-
ing Wingate anaerobic capacity tests in our laboratory
was shown to be 3%, with a CV of 0.26 and an intraclass
correlation coefficient of 0.89 for mean power.
Blood chemistry assessment. Participants refrained
from exercise, caffeine, and use of over-the-counter stimu-
lants 48 hours before baseline and follow-up testing sessions.
They were required to fast for 12 hours before donating
*20 mL of venous blood from an antecubital vein in the
forearm according to standard phlebotomy procedures.
Blood sample was collected through venipuncture (catheter-
ization) in two 7.5 mL BD Vacutainer
serum separation
tubes (Becton, Dickinson and Company, Franklin Lakes,
NJ), left at room temperature for 15 minutes, and then
centrifuged at 3500 rpm for 10 minutes using a standard,
refrigerated (4C) benchtop Thermo Scientific Heraeus
MegaFuge 40R Centrifuge (Thermo Electron North
America, LLC, West Palm Beach, FL). Serum superna-
tant was removed and stored at 80C in polypropylene
microcentrifuge tubes for later analysis. Calorimetric
assay kits were used to measure serum creatine concen-
trations (Sigma-Aldrich, St. Louis, MO).
Test-to-test variability of performing these assays yielded
a mean CV of 6.7%. Serum was also analyzed for liver
enzymes, including alkaline phosphatase, alanine trans-
aminase, and aspartate transaminase; kidney enzymes,
including creatinine and blood urea nitrogen; muscle en-
zymes, including creatine kinase and lactate dehydroge-
nase; glucose; and blood lipids, including total cholesterol,
high-density lipoprotein, low-density lipoprotein, and tri-
glycerides using a Cobas
C 111 (Roche Diagnostics,
Basel, Switzerland). The Cobas automated clinical chemis-
try analyzer was calibrated according to manufacturer
guidelines. This analyzer has been known to be highly
valid and reliable in previously published studies.
Test-to-test reliability (10 days) assessment of assays eval-
uated in this study yielded reliability CVs ranging between
0.4 and 2.4% for low control samples and 0.6 and 1.9% for
high controls with precision ranging between 0.8 and
2.4% for low and 0.5 and 1.7% for high controls.
Sleep quality, caffeine tolerance, and side effect as-
sessment. Participants were also given a short sleep qual-
ity questionnaire at each testing session to determine how
well they tolerated supplementation and if they experienced
any symptoms as a result of the supplement. The question-
naire was used to measure the quality and their sleep pat-
terns. It differentiates poor from good sleep quality by
measuring several areas (components): sleep duration, sub-
jective sleep quality, enthusiasm quality, and sleep distur-
bances over the past 48 hours. Day-to-day variability in
sleep quality questions in our laboratory yielded a CV
range of 0.22–2.2 and an intraclass correlation coefficient
range of 1.3 to 0.92.
Participants were also given a caffeine tolerance question-
naire at each testing session and they were asked to rank
the severity of their symptoms—drowsiness, tiredness,
irritability, etc. Participants were asked to rank their symp-
toms with 0 (not at all), 1 (a little), 2 (moderately), 3 (quite
a bit), and 4 (extremely). During baseline and follow-up test-
ing sessions, the questionnaires were completed immedi-
ately after the REE measurement. In addition, participants
referred to the laboratory for two screening sessions to com-
plete the questionnaires during the supplementation week.
Day-to-day variability for the caffeine inventory questions
in our laboratory ranges from 0.22 to 5.2 CV with an intra-
class correlation coefficient range of 0.2–0.88.
Statistical analysis
The sample size for our study was determined based on
previous work from our group using a similar formula and
experimental approach.
Significance was established at
0.05 with a corresponding power of 0.80 based on results
obtained one hour after testing. These calculations based
on all three Stroop domains yielded a requisite sample
size of 10 participants for the high-dose group (Cohen’s
d=0.85) and 35 for the low-dose group (Cohen’s d =
0.54) and thus we settled on 20 participants. We initiated
our analysis by inspecting data for missing values for data
missing completely (MCAR) test for data missing com-
pletely at random. This analysis showed that our data were
not significant ( p=1.0, <1.5%) and were subsequently
replaced with the series mean. Data were then analyzed
using multivariate or univariate general linear models ex-
amining between-group differences at baseline and change
from baseline. Because our cohort included women (n=3),
but an insufficient number to test for gender effects, we ad-
justed each analysis for gender. We concluded that the num-
ber of women would not produce a meaningful assessment.
Data were also examined for a treatment order effect and
considered statistically significant when the probability of
error was 0.05. Post hoc comparisons were used to compare
between-group differences when significant group differ-
ences were noted. Effect sizes were determined through par-
tial eta squared and further delineated as small (n
medium (n
=0.09), and large (n
=0.25). When examining
hematology relative to normal clinical limits, we examined
the frequency of changes in hematology outside of normal
clinical limits from baseline to follow-up using chi-square
and adjusted residual analyses to examine the likelihood
of excursions outside of clinical limits for each group as fol-
lows: (1) no change, (2) normal at baseline and high at
follow-up, and (3) high at baseline, high at follow-up,
high at baseline, and normal at follow-up. Data are reported
as mean (standard deviation), mean change from baseline
and 95% confidence intervals (CIs), and frequency of occur-
rence according to the chi-square analysis.
Thirty participants initially volunteered to participate
in the study. After signing informed consent and under-
taking a preliminary of determination of eligibility,
eight participants were deemed ineligible to participate.
Subsequently, 22 participants were randomized to start
testing, two participants opted to withdraw from the
study before starting treatments, one person failed to
pass a medical screening, and one person later withdrew
citing time constraints (Fig. 1). A total of 19 individuals
completed the study (16 males and 3 females). Overall,
participants were 21 2 years, 175 9 cm in height,
weighed 83.9 18.1 kg, and presented with a body–
mass index of 27.1 3.9 kg/m
. Body composition anal-
ysis showed the participants to be with 21.61 8.5%
body fat partitioned as fat mass (16.9 10.03 kg), fat-
free mass (60.51 12.20 kg), and lean body mass (58.3
11.72 kg). Dietary intake averaged 1600 250 calories
and comprised 155 41 g of carbohydrate, 100 28 g of
protein, and 57 14 g of fat. No significant changes in
hydration status or dietary characteristics were observed
during the course of the study and no significant treat-
ment order effects were observed for any variable.
Stroop testing and readiness to perform
Overall, no significant differences were observed be-
tween treatments for word, color, word–color, or summated
counts at baseline. However, we did observe significant
changes from baseline to follow-up for each measure as
well as for the sum of all counts. Changes in word count
were significant for PWS (6.58, 95% CI [1.34–11.79])
and PWS +150 (11.47, 95% CI [6.26–16.69]) treat-
ments, but not PLA (1.32, 95% CI [3.89 to 6.53]). A
significant group effect was also noted ( p=0.028, n
0.124) such that between-group comparisons showed
that when taking the PWS150 treatment, participants
identified 10.16 (95% CI [2.76–17.53], p=0.008, n
0.67) more words than the PLA group. No between-
group differences were observed between the PWS and
PWS150 treatments. Significant improvements were also
observed for color count for the PWS150 (8.11, 95% CI
[4.53–11.368]) and PLA treatments (4.47, 95% CI [0.89–
8.05]), but not PWS (2.32, 95% CI [1.26 to 0.73]). No
significant between-group effects were otherwise ob-
served ( p=0.77, n
=0.091). Similar pattern was also ob-
served for the word–color test. Specifically, the PWS150
(7.84, 95% CI [3.05–12.64]) and PLA treatments (5.47,
95% CI [0.68–10.27]) both demonstrated improvement;
however, the PWS (3.37, 95% CI [1.43 to 8.16]) did
not. No significant between-group effects were otherwise
observed ( p=0.42, n
=0.031). When all domains were
summed, PWS (12.26 counts, 95% CI [0.92–23.60]) and
PWS150 (27.42 counts, 95% CI [16.08–38.76]) showed
significant improvements and PLA did not (11.26 counts,
95% CI [0.077 to 22.60]; n
=0.09). Post hoc between-
group comparisons showed the PWS150 group to be sig-
nificantly greater than PLA ( p<0.05), but not different
versus PWS.
Hemodynamics and REE
We have presented the results for hemodynamic and
REE in Table 1. Overall, we observed no significant
changes in heart rate or DBP after supplement ingestion
following exercise at baseline or follow-up. We did,
however, observe a significant increase in systolic
blood pressure following bench press (10.63 beats/min,
95% CI [3.79–17.47]) and leg press testing (9.68 beats/
min, 95% CI [1.36–18.01]) on day 7 for the PWS treat-
ment. No significant changes in systolic blood pressure
were observed for the PLA or PWS150 following the
bench press (PLA 4.42 beats/min, 95% CI [11.26 to
2.42]; PWS150 0.74 beats/min, 95% CI [6.11 to
7.58]) or leg press performance (PLA 1.68 beats/min,
95% CI [10.01 to 6.64]; PWS150 0.47 beats/min,
95% CI [7.85 to 8.8]).
No significant changes were observed in heart rate or
blood pressure from pre- to postingestion at baseline or
follow-up. We also did not observe any significant differ-
ences for any postingestion hemodynamic variable from
baseline to follow-up, nor did we observe significant
changes for the resting electrocardiography recordings.
No between-group differences were observed for REE
on day 1 or 7. While no significant changes in REE
were observed from pre- to postingestion on day 1, on
day 7, the PWS group demonstrated a significant increase
in REE (156.79 kcals, 95% CI [48.78–264.8]) versus day
1. Changes for the PWS150 group (63.26 kcals, 95% CI
[44.77 to 171.28]) and PLA (76.12 kcals, 95% CI
[31.92 to 184.13]) were not significant and no between-
group differences were observed.
Performance assessment
We have presented our exercise performance findings
in Table 2 where we did not observe any significant find-
ings for any performance parameter.
Bench press. The change in bench press lifting vol-
ume from baseline to follow-up was PLA (3.72 kg, 95%
CI [72.27–79.71]), PWS (31.39 kg, 95% CI [44.6 to
107.38]), and PWS150 (25.31 kg, 95% CI [50.68 to
Table 1. Resting and Postexercise Hemodynamic Response Associated with Supplementation
Rest Postexercise
Preingestion Postingestion Bench press Leg press Wingate test
Treatment Mean SD Mean SD Mean SD Mean SD Mean SD
Heart rate (beats/min)
Baseline PLA 62.8 7.8 62.4 9.0 93.6 18.1 109.4 16.8 126.6 30.3
PWS 60.4 10.6 61.8 10.3 99.6 18.8 105.3 20.3 131.2 13.6
PWS150 59.3 9.1 59.2 7.9 110.2 13.8 122.3 22.1 137.2 15.6
Follow-up PLA 61.5 10.0 58.7 10.2 94.7 13.9 103.5 27.3 120.5 17.3
PWS 57.9 7.5 58.1 7.1 102.6 11.4 107.6 32.8 131.7 12.9
PWS150 58.6 9.7 62.2 12.9 109.4 15.2 108.7 27.4 136.9 12.1
Systolic blood pressure (mmHg)
Baseline PLA 115.6 7.1 116.4 8.2 130.2 10.7 136.4 17.4 143.8 17.5
PWS 114.1 8.7 113.3 6.9 128.3 11.0 135.4 14.4 143.1 17.2
PWS150 114.8 5.9 115.7 7.5 136.6 9.9 140.1 15.8 149.3 17.2
Follow-up PLA 117.7 9.5 116.4 8.5 125.7 14.3 134.7 16.4 144.0 17.4
PWS 113.7 7.8 116.1 8.0 138.9 13.1
145.1 15.3
151.6 17.2
PWS150 116.8 7.3 114.9 6.7 137.3 13.2 140.6 15.6 149.6 17.2
Diastolic blood pressure (mmHg)
Baseline PLA 71.1 7.3 69.0 5.8 70.6 7.5 69.0 8.8 67.0 10.0
PWS 69.5 7.2 68.5 6.6 70.7 7.7 66.8 8.4 66.0 10.4
PWS150 67.1 5.3 66.5 6.2 66.3 9.8 63.1 10.2 65.2 8.7
Follow-up PLA 71.3 7.9 68.7 7.9 67.2 8.6 65.0 9.7 67.9 10.0
PWS 71.5 7.2 67.0 7.6 62.2 8.6 62.9 7.8 61.7 9.3
PWS150 68.2 6.6 68.5 5.7 65.4 9.0 64.1 9.7 62.7 9.7
REE (kcals)
Baseline PLA 1646.79 419.4 1670.61 404.8
PWS 1689.19 405.0 1622.61 321.4
PWS150 1672.88 370.2 1725.4 414.7
Follow-up PLA 1836.5 347.6 1729.6 361.1
PWS 1815.9 391.1 1779.41 392.4
PWS150 1802.85 407.3 1788.66 464.1
Data are mean SD.
Significantly different versus baseline.
SD, standard deviation; PLA, placebo; PWS, preworkout supplements; REE, resting energy expenditure.
Leg press. The change in leg press lifting vol-
ume from baseline to follow-up was PLA (1071.67 kg,
95% CI [21.74 to 2165.08]), PWS (686.48 kg, 95% CI
[406.94 to 1779.88]), and PWS150 (93.82 kg, 95%
CI [1187.23 to 999.59]).
Wingate testing. We did not observe any significant
changes within any treatment for peak power, total
work, minimum, or the rate of fatigue. The change in
total work for the Wingate test from baseline to follow-
up was PLA (43 J, 95% CI [591.06 to 677.05]),
PWS (580.35 J, 95% CI [1178.14 to 17.45]), and
PWS150 (184.32 J, 95% CI [397.53 to 766.17]). The
change in peak power for the Wingate test from baseline
to follow-up was PLA (56.99 W, 95% CI [176.38 to
62.40]), PWS (15.42 W, 95% CI [127.98 to 97.14]),
and PWS150 (35.19 W, 95% CI [144.75 to 74.37]).
The change in minimum power for the Wingate test
from baseline to follow-up was PLA (16.07 W, 95%
CI [71.39 to 39.24]), PWS (19.97 W, 95% CI [32.18
to 72.12]), and PWS150 (60.17 W, 95% CI [110.93
to 9.41]). The change in rate of fatigue from baseline to
follow-up was PLA (0.47%, 95% CI [5.9 to 4.95]),
PWS (3.15%, 95% CI [8.27 to 1.97]), and PWS150
(0.66%, 95% CI [4.33 to 5.64]).
Blood chemistry
Overall, we did not observe any significant changes
from baseline to follow-up within each treatment group,
nor did we observe any significant differences between
treatment groups (Table 3). Furthermore, we did not ob-
serve any significant effects when examining changes for
blood parameters outside of normal clinical boundaries
(Table 4). This is not to say that some participants’
blood parameters did not exceed normal clinical limits
at follow-up. However, an examination of our data
shows these perturbations to be distributed equally across
all treatments inclusive of the PLA.
The primary aim of this study was to examine a pre-
workout supplement on the attention interference and
processing function associated with the Stroop word–
color test, performance readiness, exercise performance,
and potential alterations in hemodynamic function and
Table 2. Exercise Performance Associated with Supplementation
Baseline Follow-up
Treatment Mean SD Mean SD
Lifting volume
Bench press third set (kg) PLA 803 310 806 321
PWS 856 318 888 320
PWS150 866 371 892 320
Leg press third set (kg) PLA 6401 2173 7472 2627
PWS 7459 1932 8146 3093
PWS150 8604 3403 8510 2573
Bench press all sets (kg) PLA 2166 664 2551 1768
PWS 2241 578 2226 565
PWS150 2251 663 2276 630
Leg press all sets (kg) PLA 13,090 3487 14,161 3445
PWS 14,210 3147 14,835 4110
PWS150 16,276 9127 15,199 3665
Anaerobic capacity test
Wingate test
Total work ( J) PLA 16,687 3467 16,644 3290
PWS 16,515 3536 17,096 3329
PWS150 17,329 3650 16,644 3290
Mean power (W) PLA 551 114 560 110
PWS 566 125 562 109
PWS150 567 118 593 159
Peak power (W) PLA 1523 382 1466 451
PWS 1610 492 1595 491
PWS150 1646 411 1611 535
Minimum power (W) PLA 237 79 221 77
PWS 219 78 239 70
PWS150 235 88 189 117
Rate of fatigue (%) PLA 85.9 7.9 85.4 8.0
PWS 86.4 8.5 83.3 5.5
PWS150 86.5 10.1 87.1 11.4
Data are presented as mean SD.
PLA, placebo.
blood chemistries associated with supplementation. Our
study adds to the known literature on caffeine containing
PWS by examining two commercially available products
sold to consumers. This latter point is important as a
number of multi-ingredient PWSs are available in the
market; yet, few studies attempt to match exercise pre-
paredness and exercise performance. While the results
of our study showed a consistent pattern for improvement
in cognitive function for the PWS150 treatment, the re-
sults for the PWS group were less consistent despite
showing an overall improvement for the summated
scores of all three Stroop domains (Fig. 3). Therefore,
we accept our research hypothesis that the PWS150
group is capable of improving cognitive function, yet re-
ject the same hypothesis for the PWS treatment given its
relatively equivocal findings that were not dissimilar in
pattern to a PLA.
Despite these changes, participants in this study
showed no improvement in self-perceived readiness or
exercise performance and reject the hypotheses accom-
panying these two factors. We also did not observe any
adverse alterations in hemodynamic, hepatorenal, or
muscle enzyme function. Furthermore, although we did
observe some blood excursions beyond normal clinical
limits, they were not statistically significant and similar
among all treatment groups, inclusive of the PLA treat-
ment. Finally, we did not observe any significant changes
in REE accompanying any treatment. Therefore, we ac-
cept our hypothesis that two formulae do not adversely
alter clinical markers over a 7-day period and reject the
premise that these formulae alter REE.
A comparison of our findings with similar studies is
challenging given the complexity of multi-ingredient for-
mulae. In general, the Stroop word–color test is used to
Table 3. Hepatorenal and Muscle Enzyme
Functions Before and After Seven
Days of Supplementation
Baseline Follow-up
Mean SD Mean SD
Lipids and glucose
TC (mg/dL)
PLA 187.2 46.2 172.3 38.8
PWS 185.3 32.6 188.2 39.3
PWS150 186.6 39.0 182.9 36.6
LDL (mg/dL)
PLA 130.5 53.1 127.6 58.8
PWS 135.6 55.2 146.7 63.5
PWS150 153.5 60.0 154.0 68.5
HDL (mg/dL)
PLA 68.7 21.9 67.3 20.1
PWS 67.5 17.3 67.7 17.4
PWS150 67.4 18.5 69.4 19.4
TC:HDL ratio
PLA 2.77 0.5 2.64 0.5
PWS 2.80 0.5 2.86 0.5
PWS150 2.77 0.5 2.78 0.5
TG (mg/dL)
PLA 96.1 32.5 89.5 35.9
PWS 102.7 40.6 106.9 45.0
PWS150 118.7 63.9 96.4 35.7
Glucose (mg/dL)
PLA 111.2 26.7 101.1 14.9
PWS 108.1 22.8 112.1 18.9
PWS150 108.7 21.4 108.7 23.6
PLA 85.6 18.6 80.5 19.3
PWS 88.5 21.3 89.2 22.5
PWS150 89.0 22.0 86.5 18.7
PLA 28.4 11.5 32.6 21.5
PWS 29.1 11.8 28.1 10.9
PWS150 30.9 13.6 28.9 10.6
PLA 30.0 9.5 30.0 12.7
PWS 29.8 9.3 28.8 9.0
PWS150 26.8 7.6 29.7 11.8
CK (U/L)
PLA 312 257 660 1,166
PWS 298 237 260 176
PWS150 251 148 322 205
PLA 178 36 184 56
PWS 174 29 175 27
PWS150 175 35 173 32
BUN (mg/dL)
PLA 18.5 5.7 17.0 3.5
PWS 17.2 4.5 17.1 4.5
PWS150 17.7 5.4 17.5 4.8
Creatinine (mg/dL)
PLA 1.34 0.3 1.32 0.3
PWS 1.34 0.2 1.32 0.2
PWS150 1.28 0.2 1.29 0.2
Table 3. (Continued)
Baseline Follow-up
Mean SD Mean SD
BUN:creatinine ratio
PLA 14.1 4.3 13.3 3.7
PWS 13.2 4.1 13.3 4.3
PWS150 14.0 4.5 13.7 3.6
Creatine (lM)
PLA 191.7 69.9 205.7 82.1
PWS 191.6 80.3 218.1 98.4
PWS150 211.1 86.8 235.1 158.4
Data are mean SD for ALP, ALT, AST, CK, LDH, BUN, and
*Represents p<0.05 difference from day 0. Conversions: mg/
dL to mmol/L multiple respective values by TG (0.0133), glu-
cose (0.0555), and total-C, HDL-C, and LDL-C by 0.0259.
ALP, alkaline phosphatase; ALT, alanine transaminase; AST,
aspartate transaminase; CK, creatine kinase; BUN, blood urea ni-
trogen; LDH, lactate dehydrogenase; TC, total cholesterol; HDL,
high-density lipoprotein; LDL, low-density lipoprotein; TG, tri-
measure neuropsychology in three basic domains. The
word test assesses post left hemisphere function and
reading skills, the color test examines the dominant
temporal-occipital areas of the posterior right hemi-
sphere, and the word–color test examines prefrontal cortex
executive functions.
A common ingredient to each for-
mula is caffeine, whereby acute ingestion of caffeine has
been shown to improve Stroop testing, whereby dose may
affect testing outcomes. For example, Foreman et al. previ-
ously demonstrated that while 150 mg had no effect on
Table 4. Change in Blood Chemistries Outside of Normal Clinical Limits
Placebo PWS PWS150
Baseline/Follow-up N%N%N% Sign.
Lipids and glucose
Total cholesterol Normal/Normal 10 53 11 58 9 47 0.88
Normal/High 2 11 3 16 4 21
High/High 2 11 3 16 2 11
High/Normal 5 26 2 11 4 21
LDL-C Normal/Normal 4 21 4 21 4 21 0.42
Normal/High 9 47 12 63 13 68
High/High 1 5 2 11 0 0
High/Normal 5 26 1 5 2 11
HDL-C Normal/Normal 19 100 19 100 18 95 0.36
Normal/Low 0 0 0 0 0 0
Low/Low 0 0 0 0 1 5
Low/Normal 0 0 0 0 0 0
Triglycerides Normal/Normal 18 95 14 74 14 74 0.22
Normal/High 1 5 0 0 0 0
High/High 0 0 3 16 2 11
High/Normal 0 0 2 11 3 16
Glucose Normal/Normal 5 26 6 32 7 37 0.40
Normal/High 6 32 8 42 9 47
High/High 3 16 4 21 2 11
High/Normal 5 26 1 5 1 5
Creatinine Normal/Normal 13 68 14 74 16 84 0.13
Normal/High 3 16 2 11 0 0
High/High 2 11 0 0 2 11
High/Normal 1 5 3 16 1 5
BUN Normal/Normal 11 58 12 63 13 68 0.38
Normal/High 3 16 2 11 3 16
High/High 2 11 1 5 2 11
High/Normal 3 16 4 21 1 5
LDH Normal/Normal 18 95 19 100 19 84 0.08
Normal/High 0 0 0 0 0 0
High/High 1 5 0 0 0 0
High/Normal 0 0 0 0 0 0
Creatine kinase Normal/Normal 10 53 10 53 12 63 0.10
Normal/High 4 21 1 5 5 26
High/High 4 21 5 26 2 11
High/Normal 1 5 3 16 0 0
ALP Normal/Normal 19 100 19 100 19 100 0.09
Normal/High 0 0 0 0 0 0
High/High 0 0 0 0 0 0
High/Normal 0 0 0 0 0 0
ALT Normal/Normal 17 89 18 95 18 94 0.28
Normal/High 0 0 0 0 0 0
High/High 2 11 0 0 0 0
High/Normal 0 0 1 5 1 5
AST Normal/Normal 18 95 18 95 17 89 0.40
Normal/High 0 0 1 5 0 0
High/High 1 5 0 0 2 11
High/Normal 0 0 0 0 0 0
Data are frequency of occurrence as N, %. Significance is by chi-square analysis.
Stroop performance, ingestion of 250 mg had a deleteri-
ous effect on performance outcomes.
Hogervorst et al.
showed that caffeine supplementation before (150 mg/L)
and during (6 mL/kg) exercise improved memory, concen-
tration, and complex reaction times in athletes after exer-
cise; however, higher doses of caffeine (225 and 320 mg/
L) did not cause additional effects.
In addition, Judelson
et al.
did not observe any effects at 3 or 6 mg/kg/day of
caffeine supplementation for 5 days on cognitive perfor-
mance, psychomotor skills, and mood. However, others
have shown that ingestion of caffeine improves executive
function and improves facilitation and faster processing
when ingested up to 3 mg/kg.
Given the average weight
of our participants (83.9 18.1 kg), the results of our find-
ings in the PWS150 group would be congruent with the
previous literature. The inconsistent response of the PWS
group could be attributed to a lower caffeine dose.
Despite the improvements in cognitive function, we
did not observe any changes in perceived readiness to
perform as measured by a visual analogue scale. Our re-
sults are in agreement with Gonzalez et al.
reported no significant change in feelings of energy
when ingesting a preworkout supplement containing
taurine, glucuronolactone, caffeine, leucine, isoleucine,
valine, arginine and glutamine, dicreatine citrate, and
beta-alanine. To the contrary, Hoffman et al. observed
a significant increase in feelings of energy and focus ac-
companying a supplement containing vitamin C, vinpo-
cetine, potassium, caffeine anhydrous, n-acetyl-l-
tyrosine, 5-hydroxytryptophan, beta-alanine, yohimbine
bark extract, sulbutiamine, hordenine, n-methyltyramine,
and St. John’s Wort extract, matched by an improvement
in reaction time.
Similar to our study, no improvements
in exercise performance were observed. A similar ingre-
dient discussed within our discussion that may affect per-
formance readiness is beta-alanine; however, another
study by Hoffman et al. showed improvements in exer-
cise performance following 4 seconds of beta-alanine in-
gestion, yet there were no improvements in cognitive
One also cannot discount that the litany of in-
gredients contained in preworkout formulae might act
discordantly as, overall, our study did not show any im-
provements in exercise performance.
Finally, within the confines of our 7-day investigation,
no significant alterations were observed for blood mea-
surements denoting hepatorenal or muscle enzyme func-
tion specific to the two treatments used in this trial. This
supposition is reinforced by our chi-square analysis ex-
amining the frequency of those experiencing excursions
in blood values from baseline outside of normal clinical
limits. While these excursions did occur, they were (i)
not statistically significant and (ii) generally occurred
with equal frequency among all treatment groups, inclu-
sive of the PLA. However, two cautionary findings
warrant consideration. First, readers should note that fol-
lowing enrollment, two individuals dropped out of the
study due to intolerance to the PWS150 treatment. It
should also be noted that systolic blood pressure did in-
crease significantly postexercise following the PWS
treatment. While we cannot provide an explanation as
to why this lower dose formula caused this finding, we
would like to point out that there was no significant
FIG. 3. Data represent the mean change 95% confidence interval from baseline to follow-up in Stroop testing-
associated treatment. Statistical significance is noted as (a) significant versus placebo ( =0.008), (b) significant versus
PWS (<0.03), and (c) significant versus PWS (<0.05). PWSs, preworkout supplements.
change in blood pressure following PWS supplement in-
gestion at rest and the increase in blood pressure did
not exceed levels associated with resting hypertension.
Hence, one must consider the statistical versus clinical
significance of this particular finding.
A strength of our study is that we recruited participants
with at least 6 months of strength training experience, in-
clusive of some of the performance parameters examined
in the trial, thus minimizing training and familiarity
effects. Furthermore, we employed a crossover design
statistically adjusted for gender. This latter point is im-
portant as it is not atypical for similar trials using
mixed gender cohorts to report findings without such
adjustments. This inadvertently assumes that men and
women will respond similarly to supplementation. A lim-
itation to the study is the relatively short length of the
study, whereas a longer trial would likely provide a
more robust assessment of the potential for such a sup-
plement routine. Furthermore, we did not record actual
caffeine intake and cannot discount potential caffeine/
stimulant habituation effects despite having participants
abstain from caffeine for 4 hours prior testing. Based
on our a priori power calculations, our results appear
to be adequate to examine the PWS150 formula, but
are still underpowered to answer questions regarding
the PWS. However, the products examined are sold
under the proviso of an intended, immediate performance
effect, irrespective of caffeine or stimulant familiarity.
Furthermore, previous work from our group examining
a similar PWS and formulation showed continuous im-
provement in Stroop testing over an 8-week period.
While the results of our study demonstrated an increase
in cognitive performance using a higher dosed formula (i.e.,
PWS150) they were unmatched by perceived readiness, ex-
ercise performance, hematology, or adverse alterations in
pre- and post-exercise hemodynamic responses to exercise.
However, given the PWS150 effect on cognitive perfor-
mance, future research may wish to consider examining
more task-related performance studies. We also believe
that future studies of this nature should consider a caffeine-
only group as a means of experimental control so as to delin-
eate potential caffeine versus formulaic response. Finally,
we have attempted to extend the body of adverse effect
reporting in our analysis regarding blood chemistry excur-
sions outside of normal clinical limits. In general, we believe
that reports on potential side effects are generally under-
reported and the sports supplement field as a whole could im-
prove using more robust reporting techniques.
Availability of data and materials: Data and/or statisti-
cal analyses are available upon request on a case-by-case
basis for noncommercial scientific inquiry and/or educa-
tional use as long as IRB restrictions and research agree-
ment terms are not violated.
This study was supported by Nutrabolt (Bryan, TX)
through an unrestricted research grant provided to
Texas A&M University. The Director of Clinical Science
at Nutrabolt assisted in study design, data analysis, and
interpretation and provided comments on the manuscript.
However, the sponsor was not involved in data collection
or data entry and there were no restrictions on publication
of the data or preparation of this article. As stated above,
competing interests were supervised and managed by a
university-approved management plan to ensure that
data were accurately reported.
Authors’ Contributions
M.S.K. served as study coordinator and assisted with
data collection, data analysis, and manuscript prepara-
tion. Y.P.J., P.B.C., A.O., R.D., and S.Y.S. assisted in
data collection and sample analysis. C.R. serves as co-
ordinator of the Exercise and Sport Nutrition Labora-
tory and as project manager. M.G. assisted in research
design and consultation. P.S.M. served as study quality
assurance manager. C.P.E. serves as Research Associ-
ate in the Exercise and Sport Nutrition Laboratory
and as Director of Clinical Sciences at Nutrabolt and
served as a scientific liaison to the sponsor and assisted
with data analysis and manuscript preparation. R.B.K
obtained the grant, served as study PI, and assisted in
the design of the study, data analysis, and manuscript
preparation. All authors read and approved the final
The authors would like to thank the individuals who
participated in this study as well as Tyler Grubic, Brit-
tany Sanchez, Adriana Coletta, and Aimee Reyes at the
Exercise and Sport Nutrition Laboratory at Texas A&M
University who assisted with data collection. The au-
thors would also like to thank the Center for Transla-
tional Research in Aging and Longevity for providing
nursing support and Dr. J.P. Bramhall for providing
medical oversight.
Author Disclosure Statement
C.P.E. serves as a Director of Clinical Sciences for
Nutrabolt and is a Research Associate in the ESNL.
Dr. C.P.E. also works as a scientific consultant for Naturally
Slim and Catapult Health. R.B.K. serves as a university-
approved scientific advisor for Nutrabolt. P.S.M. serves
as quality assurance supervisor in accordance with a con-
flict of interest management plan that was approved by
the university’s research and compliance office, the internal
review board, and office of grants and contracts and moni-
toredbyresearchcompliance. Remaining investigators
have no competing interests to declare. The results from
this study do not constitute endorsement by the authors
and/or the institution concerning the nutrients investigated.
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Address correspondence to:
Conrad P. Earnest, PhD
Exercise and Sport Nutrition Laboratory
Department of Health and Kinesiology
Texas A&M University
College Station, TX 77843-4243
... Recent work from our group has demonstrated that combining various combinations of caffeine, nitrate, creatine, and β-alanine as part of a pre-workout powdered drink formula had some positive effects on cognitive and/or exercise performance [28][29][30]. The aim of this study was to examine the effects of consuming a "ready-to-drink" (RTD) version of a market leading pre-workout supplement. ...
... While the relative doses of caffeine contained in the RTD studied were slightly less than recommendations, we found that ingesting this RTD prior to exercise (acute) and/or for 6 days (short-term) promoted better maintenance of 1-RM strength and muscle endurance. These findings support our prior reports [28][29][30] as well as previous studies reporting ergogenic benefits of consuming caffeine containing energy drinks on exercise and/or cognitive performance [14,[35][36][37][38][39][40]. It is possible that since caffeine was ingested with other nutrients, there may be synergistic effects thereby reducing the need to ingest as much caffeine [3]. ...
... These studies generally demonstrate that nitrate supplementation prior to exercise can affect endurance and high-intensity intermittent exercise performance. For this reason, addition of nitrates to pre-workout supplements have also been of interest [9,12,23,[28][29][30]46,[49][50][51][52][53]. Results of the present study support prior reports indicating that acute and/or short-term ingestion of supplements containing nitrates prior to exercise can affect muscular strength and/or endurance. ...
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In a double-blind, randomized and crossover manner, 25 resistance-trained participants ingested a placebo (PLA) beverage containing 12 g of dextrose and a beverage (RTD) containing caffeine (200 mg), β-alanine (2.1 g), arginine nitrate (1.3 g), niacin (65 mg), folic acid (325 mcg), and Vitamin B12 (45 mcg) for 7-days, separated by a 7–10-day. On day 1 and 6, participants donated a fasting blood sample and completed a side-effects questionnaire (SEQ), hemodynamic challenge test, 1-RM and muscular endurance tests (3 × 10 repetitions at 70% of 1-RM with the last set to failure on the bench press (BP) and leg press (LP)) followed by ingesting the assigned beverage. After 15 min, participants repeated the hemodynamic test, 1-RM tests, and performed a repetition to fatigue (RtF) test at 70% of 1-RM, followed by completing the SEQ. On day 2 and 7, participants donated a fasting blood sample, completed the SEQ, ingested the assigned beverage, rested 30 min, and performed a 4 km cycling time-trial (TT). Data were analyzed by univariate, multivariate, and repeated measures general linear models (GLM), adjusted for gender and relative caffeine intake. Data are presented as mean change (95% CI). An overall multivariate time × treatment interaction was observed on strength performance variables (p = 0.01). Acute RTD ingestion better maintained LP 1-RM (PLA: −0.285 (−0.49, −0.08); RTD: 0.23 (−0.50, 0.18) kg/kgFFM, p = 0.30); increased LP RtF (PLA: −2.60 (−6.8, 1.6); RTD: 4.00 (−0.2, 8.2) repetitions, p = 0.031); increased BP lifting volume (PLA: 0.001 (−0.13, 0.16); RTD: 0.03 (0.02, 0.04) kg/kgFFM, p = 0.007); and, increased total lifting volume (PLA: −13.12 (−36.9, 10.5); RTD: 21.06 (−2.7, 44.8) kg/kgFFM, p = 0.046). Short-term RTD ingestion maintained baseline LP 1-RM (PLA: −0.412 (−0.08, −0.07); RTD: 0.16 (−0.50, 0.18) kg/kgFFM, p = 0.30); LP RtF (PLA: 0.12 (−3.0, 3.2); RTD: 3.6 (0.5, 6.7) repetitions, p = 0.116); and, LP lifting volume (PLA: 3.64 (−8.8, 16.1); RTD: 16.25 (3.8, 28.7) kg/kgFFM, p = 0.157) to a greater degree than PLA. No significant differences were observed between treatments in cycling TT performance, hemodynamic assessment, fasting blood panels, or self-reported side effects.
... The Stroop Word-Color test was performed immediately before and after the pre-and-post-CMJAS, to determine any effects of supplementation and exercise on attention, interference, and cognition [30]. The test included a page composed of one hundred names of different color words printed in black ink (CW), a page containing one hundred Xs printed in different colors (C), and a final page with one hundred words from the first page printed in colors from the second page, where the ink color did not match the name of the color word (W). ...
... Each correct answer earned one point, and if the participant could repeat the pages within the period, the correct responses were included again. The first two pages evaluate congruence, while the third page evaluates incongruence or interference to determine the appropriate word, independent of the color [30]. ...
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Background Beetroot juice (BJ) and caffeine (CAF) are considered as ergogenic aids among athletes to enhance performance, however, the ergogenic effects of BJ and CAF co-ingestion are unclear during team-sport-specific performance. This study aimed to investigate the acute effects of BJ and CAF co-ingestion on team-sport-specific performance, compared with placebo (PL), BJ, and CAF alone. Method Sixteen semi-professional male soccer players (age: 19.8 ± 2.2 years, body mass: 69.2 ± 6.1 kg, height: 177.3 ± 6.0 cm) completed four experimental trials using a randomized, double-blind study design: BJ + CAF, CAF + PL, BJ + PL, and PL + PL. Countermovement jump with arm swing (CMJAS) performance and cognitive function by Stroop Word-Color test were evaluated before and after the Yo–Yo Intermittent Recovery Test level 1 (YYIR1). Also, rate of perceived exertion (RPE), heart rate, and gastrointestinal (GI) discomfort were measured during each session. Results No significant differences were shown between test conditions for total distance covered in YYIR1 (BJ + CAF: 1858 ± 455 m, CAF + PL: 1798 ± 422 m, BJ + PL: 1845 ± 408 m, PL + PL 1740 ± 362 m; p = 0.55). Moreover, CMJAS performance, cognitive function, and RPE during the YYIR1 were not significantly different among conditions (p > 0.05). However, the average heart rate during the YYIR1 was higher in CAF + PL compared to PL + PL (by 6 ± 9 beats/min; p < 0.05), and GI distress was greater in BJ + CAF compared to PL + PL (by 2.4 ± 3.6 a.u.; p < 0.05). Conclusion These results suggest, neither acute co-ingestion of BJ + CAF nor BJ or CAF supplementation alone significantly affected team-sport-specific performance compared to the PL treatment.
... A formula containing theacrine and caffeine with weight ratio 2:1 to 4:1 induced an increase in energy of at least 8%, accompanying with a decrease in fatigue at least 6% (26). A pre-workout supplement of 10 mg theacrine improved selective attention (27). 27-38% improvements in time-toexhaustion were observed in participants with supplement of 275 mg theacrine, leading athletes to sustain greater focus under fatigue for long periods (16). ...
... Test on mice showed that oral administration of theacrine (5, 10, 15 mg/kg) significantly reversed learning and memory impairment caused by central fatigue (28). Combination of theacrine (125 mg) and caffeine (150 mg) moderately improved cognitive performance as assessed by trail making test (TMT) (17) and showed modest cognitive benefits during complex decision making, potentially due to overlapping peak concentrations or enhanced bioavailability (26,27). The improved cognitive accuracy at end-of-game in all conditions may indicate a training effect in highly skilled players for allocation of resources (16). ...
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Theacrine, i.e., 1,3,7,9-tetramethyluric acid, is one of the major purine alkaloids found in leaf of a wild tea plant species Camellia kucha Hung T. Chang. Theacrine has been attracted great attentions academically owing to its diverse health benefits. Present review examines the advances in the research on the health beneficial effects of theacrine, including antioxidant effect, anti-inflammatory effect, locomotor activation and reducing fatigue effects, improving cognitive effect, hypnotic effect, ameliorating lipid metabolism and inhibiting breast cancer cell metastasis effect. The inconsistent results in this research field and further expectations were also discussed.
... In subgroup analyses of individuals with or without any type of diabetes, fasting glucose was lower in HCD groups (p = 0.003) compared to controls in patients with diabetes (six RCTs, p = 0.002) [13][14][15]38,44,46 but no difference was seen in those without diabetes (eight RCTs, p = 0.6). 5,16,23,25,27,43,45,47 There were no subgroup differences for The remaining outcomes could not be assessed due to the small number of studies. ...
... Six studies did not report the required aggregate data on the effects of HCD supplementation on anthropometric measures. 12,27,28,[31][32][33] Of these, one study found no effect of HCDs on body weight 28 and another found a lower BMI after 13 weeks of chicken meat extract (containing anserine and carnosine) compared to baseline in the intervention group. 12 One study 30 ...
... In subgroup analyses of individuals with or without any type of diabetes, fasting glucose was lower in HCD groups (p = 0.003) compared to controls in patients with diabetes (six RCTs, p = 0.002) [13][14][15]38,44,46 but no difference was seen in those without diabetes (eight RCTs, p = 0.6). 5,16,23,25,27,43,45,47 There were no subgroup differences for The remaining outcomes could not be assessed due to the small number of studies. ...
... Six studies did not report the required aggregate data on the effects of HCD supplementation on anthropometric measures. 12,27,28,[31][32][33] Of these, one study found no effect of HCDs on body weight 28 and another found a lower BMI after 13 weeks of chicken meat extract (containing anserine and carnosine) compared to baseline in the intervention group. 12 One study 30 ...
Supplementation with histidine‐containing dipeptides has been shown to improve obesity and glycaemic outcomes in animal and human studies. We conducted a systematic review and meta‐analysis of randomized controlled trials to examine these effects. Electronic databases were searched investigating the effects of histidine‐containing dipeptides supplementation on anthropometric and glycaemic outcomes. Meta‐analyses were performed using random‐effects models to calculate the weighted mean difference and 95% confidence interval. There were 30 studies for the systematic review and 23 studies pooled for meta‐analysis. Histidine‐containing dipeptide groups had a lower waist circumference (WMD [95% CI] = −3.53 cm [−5.65, −1.41], p = 0.001) and HbA1c level (WMD [95% CI] = −0.76% (8.5 mmol/mol) [−1.29% (14.3 mmol/mol), −0.24% (2.8 mmol/mol)], p = 0.004) at follow‐up compared with controls. In sensitivity analyses of studies with low risk of bias, waist circumference, HbA1c, and fasting glucose levels (WMD [95% CI] = −0.63 mmol/L [−1.09, −0.18], p = 0.006) were significantly lower in intervention groups versus controls. There was also a trend toward lower fat mass (p = 0.09), insulin resistance (p = 0.07), and higher insulin secretion (p = 0.06) in intervention versus control groups. Supplementation with histidine‐containing dipeptides may reduce central obesity and improve glycaemic outcomes. Further studies exploring histidine‐containing dipeptide use in obesity and diabetes prevention and treatment are warranted.
... In subgroup analyses of individuals with or without any type of diabetes, fasting glucose was lower in HCD groups (p = 0.003) compared to controls in patients with diabetes (six RCTs, p = 0.002) [13][14][15]38,44,46 but no difference was seen in those without diabetes (eight RCTs, p = 0.6). 5,16,23,25,27,43,45,47 There were no subgroup differences for The remaining outcomes could not be assessed due to the small number of studies. ...
... Six studies did not report the required aggregate data on the effects of HCD supplementation on anthropometric measures. 12,27,28,[31][32][33] Of these, one study found no effect of HCDs on body weight 28 and another found a lower BMI after 13 weeks of chicken meat extract (containing anserine and carnosine) compared to baseline in the intervention group. 12 One study 30 ...
... Cognitive function was assessed with the Stroop word-color test before and after supplementation and 10 min following the progressive specific taekwondo test [42]. The test has three pages including a word page printed with black words (W), a page containing "XXXX'' printed in different colors (C), a final page combines "RED", "GREEN" and "BLUE" words from the first page printed with colors from the second page, where the ink color did not match with text of the color word (CW). ...
Full-text available
Studies have shown that nitrate (NO3 −)-rich beetroot juice (BJ) supplementation improves endurance and high-intensity intermittent exercise. The dose-response effects on taekwondo following BJ supplementation are yet to be determined. This study aimed to investigate two acute doses of 400 mg of NO3 − (BJ-400) and 800 mg of NO3 − (BJ-800) on taekwondo-specific performance and cognitive function tests compared with a placebo (PL) and control (CON) conditions. Eight trained male taekwondo athletes (age: 20 ± 4 years, height: 180 ± 2 cm, body mass: 64.8 ± 4.0 kg) completed four experimental trials using a randomized, double-blind placebo-controlled design: BJ-400, BJ-800, PL, and CON. Participants consumed two doses of BJ-400 and BJ-800 or nitrate-depleted PL at 2.5 h prior to performing the Multiple Frequency Speed of Kick Test (FSKT). Countermovement jump (CMJ) was performed before the (FSKT) and PSTT, whereas cognitive function was assessed (via the Stroop test) before and after supplementation and 10 min following PSTT. Blood lactate was collected before the CMJ tests immediately and 3 min after the FSKT and PSST; rating of perceived exertion (RPE) was recorded during and after both specific taekwondo tests. No significant differences (p > 0.05), with moderate and large effect sizes, between conditions were observed for PSTT and FSKT performances. In addition, blood lactate, RPE, heart rate, and CMJ height were not significantly different among conditions (p > 0.05). However, after the PSTT test, cognitive function was higher in BJ-400 compared to other treatments (p < 0.05). It was concluded that acute intake of 400 and 800 mg of NO3 − rich BJ reported a moderate to large effect size in anaerobic and aerobic; however, no statistical differences were found in taekwondo-specific performance.
... Of the 30 studies included, 17 did not supplement with HCDs. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] While it can be argued that supplementation with β-alanine may increase skeletal muscle HCD content, supplementation with histidine does not appear to alter HCD content in humans. 19,20 Both precursors also have biological actions independent from their role in HCD metabolism. ...
... These changes were accompanied with improvements in brain network connectivity [180] and cerebral blood flow as well as decreased secretion of proinflammatory markers [181]. Ingestion of carnosine-containing formulas also resulted in promising cognitive outcomes in RCTs of cognitively intact elderly [182] and patients with moderate probable AD [183] as well as improved reaction time and attentiveness [184,185] or mood [186] in young, healthy volunteers. ...
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Neurological, neurodegenerative, and psychiatric disorders represent a serious burden because of their increasing prevalence, risk of disability, and the lack of effective causal/disease-modifying treatments. There is a growing body of evidence indicating potentially favourable effects of carnosine, which is an over-the-counter food supplement, in peripheral tissues. Although most studies to date have focused on the role of carnosine in metabolic and cardiovascular disorders, the physiological presence of this di-peptide and its analogues in the brain together with their ability to cross the blood-brain barrier as well as evidence from in vitro, animal, and human studies suggest carnosine as a promising therapeutic target in brain disorders. In this review, we aim to provide a comprehensive overview of the role of carnosine in neurological, neurodevelopmental, neurodegenerative, and psychiatric disorders, summarizing current evidence from cell, animal, and human cross-sectional, longitudinal studies, and randomized controlled trials.
Context: Cardiovascular disease is a major public health problem and represents a significant burden of disease globally. Lifestyle interventions have their limitations and an intervention that will effectively address cardiovascular risk factors to help reduce this growing burden of disease is required. Objective: Carnosine and other histidine-containing dipeptides (HCDs) have exerted positive effects on cardiovascular risk factors and diseases in animal and human studies. The authors conducted a systematic review and meta-analysis examining the effects of HCDs on cardiovascular outcomes in line with the PRISMA guidelines. Data sources: The Medline, Medline in process, Embase, Cumulative Index of Nursing and Allied Health, and All EBM databases were searched from inception until January 25, 2019, for randomized controlled trials (RCTs) examining the effects of HCDs on cardiovascular outcomes, compared with placebo or controls. Data extraction: Basic characteristics of the study and populations, interventions, and study results were extracted. The grading of recommendations assessment, development, and evaluation approach was used to assess the quality of evidence for each outcome. Data analysis: A total of 21 studies were included. Of these, 18 were pooled for meta-analysis (n = 913). In low risk of bias studies, HCD-supplemented groups had lower total cholesterol (n = 6 RCTs; n = 401; weighted mean difference [WMD], -0.32 mmol/L [95%CI, -0.57 to -0.07], P = 0.01) and triglyceride levels (n = 6 RCTs; n = 401; WMD, -0.14 mmol/L [95%CI, -0.20 to -0.08], P < 0.001) compared with controls. In studies using carnosine alone, triglycerides levels were also lower in the intervention group vs controls (n = 5 RCTS; n = 309; P < 0.001). There were no significant differences in blood pressure, heart rate, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol (HDL-C) or the total cholesterol to HDL-C ratio between groups. Conclusions: Carnosine and other HCDs may have a role in improving lipid profiles. Larger studies with sufficient follow-up are necessary to confirm these findings and explore the use of HCDs in the prevention of cardiovascular diseases. Systemic review registration: PROSPERO registration no.: CRD42017075354.
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Background The purpose of this study was to examine whether ingesting a pre-workout dietary supplement (PWS) with and without synephrine (S) during training affects training responses in resistance-trained males. Methods Resistance-trained males (N = 80) were randomly assigned to supplement their diet in a double-blind manner with either a flavored placebo (PLA); a PWS containing beta-alanine (3 g), creatine nitrate as a salt (2 g), arginine alpha-ketoglutarate (2 g), N-Acetyl-L-Tyrosine (300 mg), caffeine (284 mg), Mucuna pruiriens extract standardized for 15% L-Dopa (15 mg), Vitamin C as Ascorbic Acid (500 mg), niacin (60 mg), folate as folic acid (50 mg), and Vitamin B12 as Methylcobalamin (70 mg); or, the PWS supplement with Citrus aurantium extract containing 20 mg of synephrine (PWS + S) once per day for 8-weeks during training. Participants donated a fasting blood sample and had body composition (DXA), resting heart rate and blood pressure, cognitive function (Stroop Test), readiness to perform, bench and leg press 1 RM, and Wingate anaerobic capacity assessments determined a 0, 4, and 8-weeks of standardized training. Data were analyzed by MANOVA with repeated measures. Performance and cognitive function data were analyzed using baseline values as covariates as well as mean changes from baseline with 95% confidence intervals (CI). Blood chemistry data were also analyzed using Chi-square analysis. Results Although significant time effects were seen, no statistically significant overall MANOVA Wilks’ Lambda interactions were observed among groups for body composition, resting heart and blood pressure, readiness to perform questions, 1RM strength, anaerobic sprint capacity, or blood chemistry panels. MANOVA univariate analysis and analysis of changes from baseline with 95% CI revealed some evidence that cognitive function and 1RM strength were increased to a greater degree in the PWS and/or PWS + S groups after 4- and/or 8-weeks compared to PLA responses. However, there was no evidence that PWS + S promoted greater overall training adaptations compared to the PWS group. Dietary supplementation of PWS and PWS + S did not increase the incidence of reported side effects or significantly affect the number of blood values above clinical norms compared to PLA. Conclusion Results provide some evidence that 4-weeks of PWS and/or PWS + S supplementation can improve some indices of cognitive function and exercise performance during resistance-training without significant side effects in apparently health males. However, these effects were similar to PLA responses after 8-weeks of supplementation and inclusion of synephrine did not promote additive benefits. Trial registration This trial (NCT02999581) was retrospectively registered on December 16th 2016.
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Background The purpose of this study was to examine the effects of acute ingestion of a pre-workout dietary supplement (PWS) with and without p-synephrine (S) on perceptions of readiness to perform, cognitive function, exercise performance, and markers of safety. Methods In a randomized, double-blind, and counterbalanced manner; 25 healthy and recreationally active male and female participants ingested a flavored maltodextrin placebo (PLA), a PWS containing beta-alanine (3 g), creatine nitrate as a salt (2 g), arginine alpha-ketoglutarate (2 g), N-Acetyl-L-Tyrosine (300 mg), caffeine (284 mg), Mucuna pruiriens extract standardized for 15% L-Dopa (15 mg), Vitamin C as Ascorbic Acid (500 mg), niacin (60 mg), folate as folic acid (50 mg), and Vitamin B12 as Methylcobalamin (70 mg) with 2 g of maltodextrin and flavoring; or, the PWS with Citrus aurantium (PWS + S) extract standardized for 30% p-synephrine (20 mg). Participants had heart rate (HR), blood pressure, resting energy expenditure (REE), 12-lead electrocardiograms (ECG), perceptions about readiness to perform, cognitive function (Stroop Color-Word test), bench and leg press performance (2 sets of 10 repetitions at 70% of 1RM and 1 set to failure), and Wingate anaerobic capacity (WAC) sprint performance determined as well as donated blood samples prior to and/or following exercise/supplementation. Data were analyzed by MANOVA with repeated measures as well as mean changes from baseline with 95% confidence intervals (CI). Results No clinically significant differences were observed among treatments in HR, blood pressure, ECG, or general clinical blood panels. There was evidence that PWS and PWS + S ingestion promoted greater changes in REE responses. Participants reported higher perception of optimism about performance and vigor and energy with PWS and PWS + S ingestion and there was evidence that PWS and PWS + S improved changes in cognitive function scores from baseline to a greater degree than PLA after 1 or 2 h. However, the scores in the PWS + S treatment did not exceed PLA or PWS responses at any data point. No statistically significant differences were observed among treatments in total bench press lifting volume, leg press lifting volume or WAC sprint performance. Conclusions Within the confines of this study, ingestion of PWS and/or PWS + S prior to exercise appears to be well-tolerated when consumed by young, healthy individuals. The primary effects appear to be to increase REE responses and improve perceptions about readiness to perform and cognitive function with limited to no effects on muscular endurance and WAC. The addition of 20 mg of p-synephrine to the PWS provided limited to no additive benefits. Trial registration This trial (NCT02952014) was retrospectively registered on September 13th 2016.
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Objective To conduct a systematic review and metaanalysis of the evidence on the effects of β-alanine supplementation on exercise capacity and performance. Design This study was designed in accordance with PRISMA guidelines. A 3-level mixed effects model was employed to model effect sizes and account for dependencies within data. Data sources 3 databases (PubMed, Google Scholar, Web of Science) were searched using a number of terms ('β-alanine' and 'Beta-alanine' combined with 'supplementation', 'exercise', 'training', 'athlete', 'performance' and 'carnosine'). Eligibility criteria for selecting studies Inclusion/exclusion criteria limited articles to double-blinded, placebo-controlled studies investigating the effects of β-alanine supplementation on an exercise measure. All healthy participant populations were considered, while supplementation protocols were restricted to chronic ingestion. Cross-over designs were excluded due to the long washout period for skeletal muscle carnosine following supplementation. A single outcome measure was extracted for each exercise protocol and converted to effect sizes for meta-analyses. Results 40 individual studies employing 65 different exercise protocols and totalling 70 exercise measures in 1461 participants were included in the analyses. A significant overall effect size of 0.18 (95% CI 0.08 to 0.28) was shown. Meta-regression demonstrated that exercise duration significantly (p=0.004) moderated effect sizes. Subgroup analyses also identified the type of exercise as a significant (p=0.013) moderator of effect sizes within an exercise time frame of 0.5-10 min with greater effect sizes for exercise capacity (0.4998 (95% CI 0.246 to 0.753)) versus performance (0.1078 (95% CI -0.201 to 0.416)). There was no moderating effect of training status (p=0.559), intermittent or continuous exercise (p=0.436) or total amount of β-alanine ingested (p=0.438). Co-supplementation with sodium bicarbonate resulted in the largest effect size when compared with placebo (0.43 (95% CI 0.22 to 0.64)). Summary/conclusions β-alanine had a significant overall effect while subgroup analyses revealed a number of modifying factors. These data allow individuals to make informed decisions as to the likelihood of an ergogenic effect with β-alanine supplementation based on their chosen exercise modality. © 2016 BMJ Publishing Group Ltd & British Association of Sport and Exercise Medicine.
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PurposeCaffeine-containing energy drinks (EDs) are currently used as ergogenic aids to improve physical performance in a wide variety of sport disciplines. However, the outcomes of previous investigations on this topic are inconclusive due to methodological differences, especially, in the dosage of the active ingredients and the test used to assess performance. Methods We performed a systematic review and meta-analysis of published studies to evaluate the effects of acute ED intake on physical performance. The search for references was conducted in the databases PubMed, ISI Web of Knowledge and SPORTDiscus until December 2015. ResultsThirty-four studies published between 1998 and 2015 were included in the analysis. Using a random-effects model, effect sizes (ES) were calculated as the standardized mean difference. Overall, ED ingestion improved physical performance in muscle strength and endurance (ES = 0.49; p < 0.001), endurance exercise tests (ES = 0.53; p < 0.001), jumping (ES = 0.29; p = 0.01) and sport-specific actions (ES = 0.51; p < 0.001), but not in sprinting (ES = 0.14; p = 0.06). The meta-regression demonstrated a significant association between taurine dosage (mg) and performance (slope = 0.0001; p = 0.04), but not between caffeine dosage (mg) and performance (slope = 0.0009; p = 0.21). ConclusionED ingestion improved performance in muscle strength and endurance, endurance exercise tests, jumping and sport-specific actions. However, the improvement in performance was associated with taurine dosage.
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Background Recent research into the use of dietary nitrates and their role in vascular function has led to it becoming progressively more popular amongst athletes attempting to enhance performance. Objective The objective of this review was to perform a systematic review and meta-analysis of the literature to evaluate the effect of dietary nitrate (NO3−) supplementation on endurance exercise performance. An additional aim was to determine whether the performance outcomes are affected by potential moderator variables. Data sourcesRelevant databases such as Cochrane Library, Embase, PubMed, Ovid, Scopus and Web of Science were searched for the following search terms ‘nitrates OR nitrate OR beetroot OR table beet OR garden beet OR red beet AND exercise AND performance’ from inception to October 2015. Study selectionStudies were included if a placebo versus dietary nitrate-only supplementation protocol was able to be compared, and if a quantifiable measure of exercise performance was ≥30 s (for a single bout of exercise or the combined total for multiple bouts). Study appraisal and synthesisThe literature search identified 1038 studies, with 47 (76 trials) meeting the inclusion criteria. Data from the 76 trials were extracted for inclusion in the meta-analysis. A fixed-effects meta-analysis was conducted for time trial (TT) (n = 28), time to exhaustion (TTE) (n = 22) and graded-exercise test (GXT) (n = 8) protocols. Univariate meta-regression was used to assess potential moderator variables (exercise type, dose duration, NO3− type, study quality, fitness level and percentage nitrite change). ResultsPooled analysis identified a trivial but non-significant effect in favour of dietary NO3− supplementation [effect size (ES) = −0.10, 95 % Cl = −0.27 to 0.06, p > 0.05]. TTE trials had a small to moderate statistically significant effect in favour of dietary NO3− supplementation (ES = 0.33, 95 % Cl = 0.15–0.50, p < 0.01). GXT trials had a small but non-significant effect in favour of dietary NO3− supplementation in GXT performance measures (ES = 0.25, 95 % Cl = −0.06 to 0.56, p > 0.05). No significant heterogeneity was detected in the meta-analysis. No statistically significant effects were observed from the meta-regression analysis. Conclusion Dietary NO3− supplementation is likely to elicit a positive outcome when testing endurance exercise capacity, whereas dietary NO3− supplementation is less likely to be effective for time-trial performance. Further work is needed to understand the optimal dosing strategies, which population is most likely to benefit, and under which conditions dietary nitrates are likely to be most effective for performance.
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Purpose: Given the important role of the brain in regulating endurance performance, this comparative study sought to determine whether professional road cyclists have superior inhibitory control and resistance to mental fatigue compared to recreational road cyclists. Methods: After preliminary testing and familiarization, eleven professional and nine recreational road cyclists visited the lab on two occasions to complete a modified incongruent colour-word Stroop task (a cognitive task requiring inhibitory control) for 30 min (mental exertion condition), or an easy cognitive task for 10 min (control condition) in a randomized, counterbalanced cross-over order. After each cognitive task, participants completed a 20-min time trial on a cycle ergometer. During the time trial, heart rate, blood lactate concentration, and rating of perceived exertion (RPE) were recorded. Results: The professional cyclists completed more correct responses during the Stroop task than the recreational cyclists (705±68 vs 576±74, p = 0.001). During the time trial, the recreational cyclists produced a lower mean power output in the mental exertion condition compared to the control condition (216±33 vs 226±25 W, p = 0.014). There was no difference between conditions for the professional cyclists (323±42 vs 326±35 W, p = 0.502). Heart rate, blood lactate concentration, and RPE were not significantly different between the mental exertion and control conditions in both groups. Conclusion: The professional cyclists exhibited superior performance during the Stroop task which is indicative of stronger inhibitory control than the recreational cyclists. The professional cyclists also displayed a greater resistance to the negative effects of mental fatigue as demonstrated by no significant differences in perception of effort and time trial performance between the mental exertion and control conditions. These findings suggest that inhibitory control and resistance to mental fatigue may contribute to successful road cycling performance. These psychobiological characteristics may be either genetic and/or developed through the training and lifestyle of professional road cyclists.
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The purpose of this study was to examine possible dose-response and time course effects of an acute bout of resistance exercise on the core executive functions of inhibition, working memory, and cognitive flexibility. Twenty-eight participants (14 females; Mage = 20.5 ± 2.1 yrs) completed a control condition and resistance exercise bouts performed at 40%, 70%, and 100% of their individual 10-repetition maximum. An executive function test battery was administered at 15-min and 180-min post-exercise to assess immediate and delayed effects of exercise on executive functioning. At 15-min post-exercise, high-intensity exercise resulted in less interference and improved reaction time (RT) for the Stroop task, while at 180-min low and moderate-intensity exercise resulted in improved performance on plus-minus and Simon tasks, respectively. These findings suggest a limited and task-specific influence of acute resistance exercise on executive function in healthy young adults.
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Background: Beta-alanine (BA) is a non-essential amino acid that can be synthesized in the liver and obtained from diet, particularly from white and red meat. Increased availability of BA via dietary supplement, may improve performance of athletes. The aim of this study was to conduct a review of the use of BA supplementation as an ergogenic aid to improve performance and fatigue resistance in athletes and non-athletes. Methods: In this systematic review, a search in PubMed and Bireme databases was performed for the terms "beta-alanine", "beta-alanine and exercise", "carnosine" or "carnosine and exercise" in the titles or abstracts. We included randomized, clinical trials published between 2005 and 2015. Results: Twenty-three studies were selected. Most of them included physically active individuals. The mean intervention period was 5.2 ± 1.8 weeks, and mean BA dose was 4.8 ± 1.3g / day. The main outcome measures were blood lactate, pH, perceived exertion, power and physical working capacity at fatigue threshold. After BA supplementation, no statistically significant difference was observed in total work, exercise performance time, oxygen consumption and time to exhaustion. Conclusion: BA supplementation seems to improve perceived exertion and biochemical parameters related to muscle fatigue and less evidence was found for improvement in performance.
Objective: Caffeine has been shown to have effects on certain areas of cognition, but in executive functioning the research is limited and also inconsistent. One reason could be the need for a more sensitive measure to detect the effects of caffeine on executive function. This study used a new non-immersive virtual reality assessment of executive functions known as JEF(©) (the Jansari Assessment of Executive Function) alongside the 'classic' Stroop Colour-Word task to assess the effects of a normal dose of caffeinated coffee on executive function. Method: Using a double-blind, counterbalanced within participants procedure 43 participants were administered either a caffeinated or decaffeinated coffee and completed the 'JEF(©)' and Stroop tasks, as well as a subjective mood scale and blood pressure pre- and post condition on two separate occasions a week apart. JEF(©) yields measures for eight separate aspects of executive functions, in addition to a total average score. Results: Findings indicate that performance was significantly improved on the planning, creative thinking, event-, time- and action-based prospective memory, as well as total JEF(©) score following caffeinated coffee relative to the decaffeinated coffee. The caffeinated beverage significantly decreased reaction times on the Stroop task, but there was no effect on Stroop interference. Conclusion: The results provide further support for the effects of a caffeinated beverage on cognitive functioning. In particular, it has demonstrated the ability of JEF(©) to detect the effects of caffeine across a number of executive functioning constructs, which weren't shown in the Stroop task, suggesting executive functioning improvements as a result of a 'typical' dose of caffeine may only be detected by the use of more real-world, ecologically valid tasks.
Theacrine (1,3,7,9-tetramethyluric acid) is a naturally occurring purine alkaloid, present in Camellia assamica variety kucha tea. Using a two-part approach in humans, the impact of theacrine (TeaCrine®, TC) was used to examine subjective dose-response, daily changes in cognitive and psychometric parameters, and changes in gas exchange and vital signs. All indicators were chosen to better ascertain the previously reported animal and human outcomes involving theacrine administration. Part 1 was a randomized, open-label, dose-response investigation in nine healthy participants whereby three participants ingested 400 mg TC per day and six participants ingested 200 mg/day. Participants recorded subjective changes in cognitive, psychometric, and exercise attributes using 150-mm anchored visual analog scale (VAS) before, and 1, 4, and 6 hours after ingestion every day for 7 consecutive days. Part 2 was a randomized, double-blind, placebo-controlled, crossover investigation in 15 healthy subjects in which all participants ingested a single 200 mg dose of TC or Placebo (PLA). Anchored VAS questionnaires were used to detect subjective changes in various aspects of physical and mental energy along with changes in gas exchange and hemodynamic parameters before, and 1, 2, and 3 hours after acute ingestion. Energy, focus, and concentration increased from baseline values in both doses with no dose-response effect. VAS responses in the 200 mg for willingness to exercise, anxiety, motivation to train and libido increased across the measurement period while no such change was seen with the 400 mg dose. After consuming a single 200 mg dose, significant group × time interaction effects were seen for energy, fatigue, and concentration. No changes in resting heart rate, gas exchange, systemic hemodynamics or side effect profiles were noted.