Effects of Amino Acids Supplement on
Physiological Adaptations to Resistance
Training
WILLIAM J. KRAEMER1,2, DISA L. HATFIELD1, JEFF S. VOLEK1, MAREN S. FRAGALA1, JAKOB L. VINGREN1,
JEFFREY M. ANDERSON1, BARRY A. SPIERING1, GWENDOLYN A. THOMAS1, JEN Y. HO1, ERIN E. QUANN1,
MIKEL IZQUIERDO3, KEIJO HÄKKINEN4, and CARL M. MARESH1,2
1
Human Performance Laboratory, Department of Kinesiology, University of Connecticut, Storrs, CT; 2Department of
Physiology and Neurobiology, University of Connecticut, Storrs, CT; 3Studies, Research and Sport Medicine Center,
Government of Navarra, SPAIN; and 4Department of Biology of Physical Activity and Neuromuscular Research Center,
University of Jyväskylä, Jyväskylä, FINLAND
ABSTRACT
C
hronic resistance exercise promotes increases in
muscle size and strength. Activation of muscle
fibers to produce force leads to a subsequent cascade of events including hormone and immune responses,
stimulation of muscle cell signaling pathways, activation of
satellite cells, and, ultimately, increases in protein synthesis
(13,16). In total, these responses promote muscle protein
accretion and improve force production capabilities. Although resistance exercise in a fasted state increases protein
synthesis, net protein balance remains negative unless
nutrients are provided (32). In particular, it seems that
provision of essential amino acids drives the net increase in
muscle protein synthesis after resistance exercise (40).
Essential amino acids serve two critical functions for
protein synthesis: 1) essential amino acids are substrates for
protein synthesis because mRNA translation cannot progress unless the entire array of amino acids are immediately
available, which highlights the importance of ingesting
essential amino acids (i.e., those that cannot be synthesized
de novo), and 2) essential amino acids are signals for
protein synthesis. Several recent studies have highlighted
the role of essential amino acids as independent signals
for translation initiation (3,5). For instance, ingesting
essential amino acids before and/or after resistance exercise
Address for correspondence: William J. Kraemer, Ph.D., FACSM, Human
Performance Laboratory, Department of Kinesiology, University of
Connecticut, 2095 Hillside Rd, U-1110, Storrs, CT 06269-1110; E-mail:
[email protected].
Submitted for publication October 2008.
Accepted for publication November 2008.
0195-9131/09/4105-1111/0
MEDICINE & SCIENCE IN SPORTS & EXERCISEÒ
Copyright Ó 2009 by the American College of Sports Medicine
DOI: 10.1249/MSS.0b013e318194cc75
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APPLIED SCIENCES
KRAEMER, W. J., D. L. HATFIELD, J. S. VOLEK, M. S. FRAGALA, J. L. VINGREN, J. M. ANDERSON, B. A. SPIERING, G. A.
THOMAS, J. Y. HO, E. E. QUANN, M. IZQUIERDO, K. HÄKKINEN, and C. M. MARESH. Effects of Amino Acids Supplement on
Physiological Adaptations to Resistance Training. Med. Sci. Sports Exerc., Vol. 41, No. 5, pp. 1111–1121, 2009. Introduction:
Previous research has demonstrated that ingestion of essential amino acids and their metabolites induce anabolic effects with the
potential to augment gains in lean body mass and strength after resistance exercise training. Purpose: The purpose of the present study
was to examine the effects of an essential amino acid-based formula (Muscle Armori (MA); Abbott Laboratories, Abbott Park, IL)
containing A-hydroxy-A-methylbutyrate (HMB) on hormonal and muscle damage markers in response to 12 wk of resistance exercise.
Methods: Seventeen healthy men (mean body mass: 77.9 T 7.2 kg; mean height: 174.3 T 12.4 cm; mean age: 22.9 T 3.8 yr) were
matched and randomized into two groups and performed 12 wk of periodized heavy resistance training while supplementing with either
MA or an isocaloric, isonitrogenous placebo (CON). Every 2 wk during the 12-wk intervention, resting blood draws were obtained, and
muscle strength and power were measured. In addition, blood draws were obtained before, during, and after a standardized resistance
exercise challenge performed pre-, mid-, and posttraining. Results: Lean body mass, muscle strength, and muscle power significantly
(P e 0.05) increased in both groups after training; however, MA supplementation augmented these responses to a significantly greater
extent when compared with the CON group. MA supplementation promoted increases in resting and exercise-induced testosterone and
resting growth hormone concentrations. In addition, MA reduced preexercise cortisol concentrations. Throughout the training protocol,
MA attenuated circulating creatine kinase and malondealdehyde compared with the CON group, suggesting that MA might have
influenced a reduction in muscle damage. Conclusion: MA supplementation beneficially affected training-induced changes in lean
body mass, muscle strength, and power, as well as hormonal responses and markers of muscle damage in response to 12 wk of
resistance exercise training when compared with an isonitrogenous control. Key Words: ENDOCRINE, ERGOGENIC, BODY
COMPOSITION, STRENGTH, HMB, AMINO ACIDS
APPLIED SCIENCES
potentiates the resistance exercise-induced activation of the
70-kDa ribosomal protein S6 kinase (p70S6K) (3), an
important enzyme for increasing translational efficiency
and protein synthesis after exercise (2). Further, it seems
that leucine has a primary and noninsulin-dependent role in
stimulating this pathway. Amino acid supplementation also
reduces circulating markers of muscle damage (e.g.,
creatine kinase [CK] and lactate dehydrogenase) after
exercise (9). Specific amino acids such as arginine have
been shown to acutely increase circulating levels of growth
hormone (GH) (7,30), whereas glutamine is purported to
have beneficial effects on the immune system and glucose
regulation during periods of intense training (1). Further,
L-arginine in particular has been shown to positively
influence muscular strength and power with training (6).
The mechanisms by which L-arginine may affect athletic
performance have yet to be elucidated; however, it might be
via changes in growth hormone and testosterone, both of
which impinge upon transcription and translation processes,
triggering enhanced muscle protein synthesis (7). Therefore,
it seems that amino acid supplementation can potentiate
responses and adaptations to resistance exercise via several
mechanisms (e.g., promoting protein synthesis, attenuating
muscle damage).
Because of the critical role of amino acids, recent
studies have investigated the efficacy of A-hydroxy-Amethylbutyrate (HMB) supplementation for promoting
resistance exercise adaptations. A-hydroxy-A-methylbutyrate is a metabolite of the amino acid leucine, a potent
stimulus of translation initiation and protein synthesis (3).
In accord with the beneficial effects of amino acid
supplementation, HMB supplementation decreases circulating markers of muscle damage (e.g., CK) after resistance
exercise and may have anticatabolic properties (11,31).
With regard to chronic adaptations, several studies of HMB
supplementation have reported positive effects on muscle
mass, body composition, and strength in men and women
(28,29,31,38). These results may be due to HMB’s ability
to attenuate protein degradation and stimulate protein
synthesis through multiple mechanisms (10,39). Recent
evidence published by Eley et al. (10) in 2007 showed that
HMB increased phosphorylation activity of the mammalian
inhibitor target of rapamycin (mTOR) pathway and mTOR
initiation factors in the muscle of cachectic mice (10). In
humans, HMB has been shown to interfere with the
ubiquitin–proteosome proteolysis pathway in human cancer
patients, thus preserving lean body mass (34).
The metabolic research supporting anabolic actions of
amino acids and HMB led us to hypothesize that an amino
acid supplement complemented with HMB would result in
increased lean body mass and strength compared with
ingestion of an isonitrogenous placebo. Here, we show for
the first time that daily supplementation with Muscle
Armori (Abbott Laboratories, Abbott Park, IL; an amino
acid supplement containing HMB) enhanced lean body mass
and performance gains from 12 wk of heavy resistance
training. We further elucidate potential mechanisms by
showing that a supplement containing HMB alters anabolic
and catabolic hormonal responses as well as markers of
membrane disruption and oxidative stress.
METHODS
Experimental Approach to the Problem
A randomized, double-blind, placebo-controlled design
was used to determine the effects of adding Muscle
Armori (Abbott Laboratories) to a resistance exercise
training program. Subjects ingested Muscle Armori (MA)
or an isonitrogenous control (CON) twice daily during a
12-wk resistance training protocol. Bench press strength,
squat strength, lower-body power, body composition,
resting hormonal concentrations, and markers of muscle
damage were measured pretraining (V annotations) (V1),
after the first six sets of 10 repetition maximums (RM) of
an acute resistance exercise protocol (AREP) or V2, week
2 (V3), week 4 (V4), week 6 (V5), week 6 for the second
AREP (V6), week 8 (V7), week 12 (V8), and the last AREP
of the 12-wk intervention (V9). Again, subjects performed a
standardized bout of acute resistance exercise at pre- (V2),
mid- (V6), and posttraining (V9) to determine resistance
exercise-induced hormonal and muscle damage responses.
All subjects were verified to be hydrated before all tests using
a handheld refractometer to measure urine specific gravity
FIGURE 1—Study design: after familiarization with the squat and bench exercise (week j1 to week 0, dashed line), subjects performed 12 wk of
periodized resistance training while supplementing with either Muscle Armori (MA) or an isocaloric, isonitrogenous control (CON) (week 0 to
week 12, solid line). Every 2 wk during the 12-wk intervention, resting blood draws were obtained, and muscle strength and power were measured
(as indicated by the L). In addition, blood draws were obtained before, during, and after a standardized resistance exercise challenge performed pre-,
mid-, and posttraining (at weeks 0, 6, and 12 as indicated by the *).
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(G1.020 indicated euhydration). The sequence of the experimental timeline can be seen in Figure 1.
Subjects
Seventeen healthy men who were recreationally active
(Mean T SD body mass: 77.9 T 7.2 kg; mean height: 174.3 T
12.4 cm; mean age: 22.9 T 3.8 yr) volunteered to participate
in the study. Study participation required that all subjects
were not currently had not been resistance training within the
previous 6 months. Each subject was screened by a physician to exclude those with orthopedic limitations or medical
conditions that would prevent them from safely participating
in the study. In addition, dietetic screening was performed by
registered dieticians to ensure that subjects were 1) on a diet
consisting of 15–20% protein, 45–55% carbohydrate, and
25–30% fat; 2) not taking creatine or HMB supplements; 3)
not smoking; 4) not taking protein or amino acid supplements; 5) not taking anabolic or catabolic hormones; and 6)
not taking medication or supplements known to influence
any of the variables measured in the study. Subjects were
carefully matched by age, body mass, vertical jump height,
and resistance training and physical activity background,
then randomly placed into either the MA (n = 8) or the CON
(n = 9) group. After an explanation of the procedures and
associated risks, all volunteers provided written informed
consent. All procedures were approved by the University of
Connecticut’s Institutional Review Board for use of human
subjects.
Diet assessment and counseling. Each subject was
screened for dietary habits before inclusion into the study.
Subjects completed 5-d diet records pretraining, midtraining, and during the last week of the training period.
After the first 5-d diet record, but before the onset of the
training period, participants received dietary counseling
by a registered dietitian to ensure that the participants
maintained their habitual dietary habits and ingested the
supplement twice daily. The registered dietitian met with
the subjects each week to review a 1-day diet record and
assure adherence to all supplement and food instructions.
Food diaries were analyzed for energy and macro/micronutrient content with NUTRITIONIST PROi (Version 4.2.0,
Axxya Systems, Stafford, TX).
Supplementation. Volunteers either received an MA
supplement (1.5 g of calcium HMB, 7 g of arginine, 7 g of
glutamine, 3 g of taurine, and 5.824 g of dextrose) or an
isocaloric, isonitrogenous control containing nonessential
amino acids (10 g of glycine, 11.5 g of alanine, 1.5 g of
glutamic acid, and 1.5 g of serine) as well as calcium citrate
(200 mg of calcium). The treatments were matched in
sensory attributes of flavor, sweetness, and acidity as well
as delivering an equivalent amount of calcium (200 mg).
Mass and calorie balance were achieved by decreasing
PROTEIN SUPPLEMENTATION AND STRENGTH TRAINING
TABLE 1. Periodization scheme.
Week
Week
Week
Week
Week
Week
Week
Week
Week
Week
Week
Week
1
2
3
4
5
6
7
8
9
10
11
12
Day 1
Day 2
Day 3
L
M
L
M
H
H
H
H
M
L
M
H
M
H
M
L
M
M
M
H
L
H
M
M
H
M
H
M
L
H
L
M
H
H
H
L
Training days were split into ‘ light,’’ ‘ moderate,’’ and ‘ heavy’’ days in a nonlinear
periodized manner. Repetition maximum (RM) zones were used to progress intensity:
‘ light’’ days consisted of a 12- to 14-RM zone, ‘ moderate’’ days consisted of an 8- to
10-RM zone, and ‘ heavy’’ days consisted of a 3- to 5-RM zone. Weight was increased
systematically if the prescribed amount of repetitions were completed.
H, heavy; L, light; M, moderate.
Medicine & Science in Sports & Exercised
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APPLIED SCIENCES
Procedures
dextrose in the placebo. Each volunteer received the
supplements in plain, white blinded packets, given in two
equal daily doses. Supplements were consumed twice per
day (once with breakfast, once with dinner) throughout the
12-wk training period. To ensure compliance, participants
completed supplement logs, met with the registered dietician, handed in empty supplement packets, and received
phone call ‘‘reminders’’ and ‘‘checks’’ at all workout
sessions.
Resistance exercise training protocol. Subjects
were familiarized with all testing and training procedures
before the onset of the study to minimize the influence
of learning effects on dependent measures. The resistance exercise training protocol consisted of a 12-wk
(36 sessions) nonlinear periodized program. The resistance
exercise program stressed all major muscle groups and
included the following exercises (or variations of) in each
session: bench presses, squats, lunges, shoulder presses,
arm curls, stiff-leg dead lifts, lat pull downs, seated rows,
calf raises, and sit-ups. Exercise volume and intensity
progressed during the training program according to previous recommendations (18,21). We used a planned nonlinear
periodization resistance training program with different
workouts during the week. Briefly, training days were split
into ‘‘light,’’ ‘‘moderate,’’ and ‘‘heavy’’ days in a nonlinear
periodized manner. Repetition maximum (RM) zones were
used to progress intensity. ‘‘Light’’ days consisted of a
12- to 14-RM zone (three sets), ‘‘moderate’’ days consisted
of an 8- to 10-RM zone (three sets), and ‘‘heavy’’ days
consisted of a 3- to 5-RM zone (three sets but five sets for
squat and bench press exercises). Weight was increased
systematically if the prescribed amount of repetitions were
completed. The planned training sequence is shown in
Table 1. Subjects also performed supplemental endurance
exercise (two to three sessions per week) in addition to their
resistance training program. Endurance exercise was included in the program because these subjects were
recreationally active and were encouraged to maintain their
normal activities in addition to the resistance training they
APPLIED SCIENCES
performed for the duration of the study. Endurance
exercises included cycling, walking, and/or jogging at
60–70% of HR reserve for at least 30 min according to
the general guidelines of the American College of Sports
Medicine. All training sessions were performed at the
University of Connecticut strength and conditioning facilities under the supervision of Certified Strength and
Conditioning Specialists by the National Strength and
Conditioning Association. Makeup sessions were allowed
if subjects missed a regularly scheduled training session;
therefore, subject compliance in this study was 100% for
the chronic training protocol.
Resting blood draws. Resting blood draws were
obtained via venipuncture by a trained phlebotomist at
pretraining (V1) and at week 2 (V3), week 4 (V4), week 6
(V5), week 8 (V7), and week 12 (V8) of the 12-wk
intervention. Whole blood was collected and transferred
into appropriate tubes for obtaining serum and plasma and
centrifuged at 1500g for 15 min at 4-C. Resulting serum
and plasma was aliquoted and stored at j80-C until
subsequent analyses.
Strength testing. One repetition maximum (1-RM)
strength was assessed in the free-weight bench press and
free-weight squat exercises using previously described
methods (20). Briefly, subjects performed a warm-up on a
cycle ergometer followed by light dynamic stretching.
Then, subjects performed 8–10 repetitions at È50% of
estimated 1-RM, followed by another set of 3–5 repetitions
at È85% of 1-RM. Three to four maximal trials separated
by 2–3 min of rest were used to determine individual 1-RM
for each resistance exercise. 1-RM testing was performed at
pretraining (V1) and at week 2 (V3), week 4 (V4), week 6
(V5), week 8 (V7), and week 12 (V8) of the 12-wk
intervention.
Power testing. Countermovement vertical jump power
was assessed using a force plate and associate software
(Accupower; Advanced Mechanical Technologies, Inc.,
Watertown, MA). After familiarization, subjects were asked
to place their hands on their hips and jump as high as they
could for three subsequent repetitions. The highest power
for the set was recorded.
Acute resistance exercise protocol. Subjects performed a standardized acute resistance exercise protocol
(AREP) in a 8 hr fasted state at pre- (V2), mid- (V6), and
posttraining (V9) to determine exercise-induced hormonal
and muscle damage responses in the blood. The AREP
consisted of six sets of 10 maximal repetitions in the squat
exercise with 2-min rest between sets. The initial load was
80% of individual 1-RM. If a subject was unable to
complete all 10 repetitions during a given set, then spotters
provided assistance until all 10 repetitions were completed;
the resistance was then decreased for subsequent sets.
Before commencing the AREP, a trained phlebotomist
inserted an indwelling Teflon cannula into a superficial
forearm vein of the subject. The cannula was kept patent with
a 10% heparin–saline solution. Venous blood samples were
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obtained at preexercise (pre), after the third set (mid),
immediately postexercise (post), and at 5 min (+5), 15 min
(+15), and 30 min (+30) postexercise. Before each blood
draw, 3 mL of blood was drawn and discarded to avoid
inadvertent dilution of the blood sample. Subsequently, whole
blood was collected and processed as previously described.
Measures of body composition, body circumferences, and tendon size. Whole body composition
was assessed by dual-energy x-ray absorptiometry (DXA)
(Prodigyi; Lunar Corporation, Madison, WI) before (V1),
at the mid-point (V5), and after (V8) the training period.
Analyses were performed by the same blinded technician
using commercial software (enCORE version 6.00.270, GE
Lunar Corporation, Madison, WI). Coefficients of variation
for lean body mass, fat mass, and bone mineral content on
repeat scans with repositioning on a group of men/women
were 0.4%, 1.4%, and 0.6%, respectively. Body circumferences were assessed at the neck, chest, upper arm, waist,
thigh, and calf by the same tester. The cross-sectional area
of the patella tendon was assessed using ultrasonography
(33) to determine connective tissue adaptations during the
12-wk resistance exercise protocol.
Biochemical Analyses
Samples were thawed one time and analyzed in duplicate
for each analyte. All AREP days were scheduled at the
same time of day to negate confounding influences of
diurnal hormonal variations.
Plasma glucose and lactate concentrations were measured
in duplicate using the STAT 2300 (Yellow Springs, Inc.,
Yellow Springs, OH). Serum total testosterone, GH, and
insulin-like growth factor 1 (IGF-1), insulin, and cortisol
were assayed via ELISA kits obtained from Diagnostic
Systems Laboratories (Webster, TX). All hormones were
measured in the same assay on the same day to avoid
compounded interassay variance. Intra-assay variance was
less than 3% for all analytes. Serum creatine kinase (CK)
was measured using colorimetric procedures at 340 nm
(Diagnostics Chemicals, Oxford, CT). Plasma malondealdehyde (MDA) was determined using colorimetric procedures at 532 nm on the basis of the formation of
thiobarbituric acid reactive substances.
Statistical Analyses
A linear model with a two-way mixed factorial ANOVA
(i.e., groups time) was used with repeated measures for
time. Linear assumptions were tested for, and sphericity
correction was made if needed with the Huynh–Feldt
correction because of higher variance in the hormones.
Any variables that did not meet the requirements were
logarithmetically corrected and tested again. All pairwise
comparisons were evaluated with Bonferroni corrections (or
LSD-equivalent and to a no Type I error rate adjustment)
for all of the comparisons. Using the nQuery AdvisorÒ
software (Statistical Solutions, Saugus, MA), the statistical
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FIGURE 2—Body mass (panel A), lean body mass (panel B), and percent body fat (panel C) values (mean T SE) before training (V1), after week 6 of
resistance exercise training (V5), and after 12 wk of resistance exercise training (V8). CON, control group; MA, Muscle Armor group. †Significant
difference from corresponding V1 value, P e 0.05; Lsignificant difference from corresponding control value, P e 0.05.
power for the n size used ranged from 0.76 to 0.87. The
power is based on a variety of probability equations by
Cohen (8) and represents the needed number of subjects to
defend the 0.05 level of significance fourfold and allow
detection of a 5% to 10% treatment effect. The test–retest
reliability of the tests used in our laboratory have had
intraclass R values ranging from 0.90 to 0.99, and this
allows for the assessment of such treatment effects with
the n size of 8–10 in a group. Significance was set at
P e 0.05.
RESULTS
FIGURE 3—Circumference (panel A) and patella tendon thickness (panel B) values (mean T SE) before training (V1), after week 6 of resistance
exercise training (V5), and after 12 wk of resistance exercise training (V8). CON, control group; MA, Muscle Armor group. †Significant difference
from corresponding V1 value, P e 0.05; Lsignificant difference from corresponding control value, P e 0.05.
PROTEIN SUPPLEMENTATION AND STRENGTH TRAINING
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APPLIED SCIENCES
Body mass, body composition, and circumferences. Body mass increased above baseline (V1)
values at posttraining (V8) in both groups; however, the
MA group had significantly greater gains than the CON
group (Fig. 2A). Changes in lean body mass (Fig. 2B)
closely reflected changes in total body mass, indicating that
increased muscle mass occurred after the periodized
resistance exercise training protocol. The MA group had
greater increases in lean body mass (Fig. 1B) as well as
lower percent body fat (Fig. 2C).
After 12 wk of resistance exercise training, both groups
showed increased circumferences of the biceps, thigh, and
chest; however, no change in waist circumference occurred
(Fig. 3A). Subjects in the MA group had greater thigh and
chest circumference than the CON group after training (at
V8). Although there was a significant increase in patella
tendon thickness in both groups, there was no difference
between groups (Fig. 3B).
Exercise performance. The MA group made significantly greater percentage gains in 1-RM strength in the
squat and bench press during the first 6 wk and posttraining
compared with the CON group (Figs. 4, A and B). Maximal
power (W) in the countermovement vertical jump also
improved at a faster rate in the MA group than that in the
CON group, yielding significantly higher percentage gains
at mid- and posttraining time points (Fig. 4C).
Hormones. The resistance exercise training protocol
significantly increased resting testosterone concentrations
above baseline (V1) values at V3 through V8 in the MA
group, but only at V4 and V7 in the CON group. The AREP
increased testosterone concentrations above preexercise
values at post, +5, and +15 in all three AREP trials. The
resistance exercise-induced increases in testosterone were
APPLIED SCIENCES
FIGURE 4—Squat 1-RM (panel A), bench 1-RM (panel B), and vertical jump power (panel C) values (mean T SE) before training (V1), after week 6
of resistance exercise training (V5), and after 12 wk of resistance exercise training (V8). CON, control group; MA, Muscle Armor group. †Significant
difference from corresponding V1 value, P e 0.05; Lsignificant difference from corresponding control value, P e 0.05.
greater in the MA group than that in the CON group
at various postexercise time points during V6 and V9.
Figure 5 displays testosterone values.
No change in resting cortisol concentrations occurred
during the training protocol. However, MA supplementation reduced preexercise cortisol values (V2, PRE) compared with baseline values. Although the AREP increased
circulating cortisol values, there were no differences
between the MA and CON groups in resistance exerciseinduced cortisol responses at any time point. Figure 6
displays the cortisol values.
Increased resting GH concentrations were apparent at V8
and V9 in the MA group only. Moreover, these values were
significantly greater than corresponding CON values.
Resistance exercise increased GH concentrations at all
postexercise time points; however, there were no differences between groups. Figure 7 displays the GH values.
Resistance exercise training had no effect on resting
IGF-1 values. The AREP increased IGF-1 concentration at
mid- and postexercise in all trials. However, there were no
differences between groups for any resting or postexercise
time point. Figure 8 displays the IGF-1 values.
There was no effect of resistance exercise training on
resting insulin concentrations. The AREP increased insulin
at +5, +15, and +30 in V2 and V9; however, this was only
significant during V9. There were no differences between
groups for any resting or postexercise time point. Figure 9
displays the insulin values.
Markers of muscle damage. Differences between
trials in circulating CK began to appear after the first
AREP. At V3, CK was dramatically elevated in the CON
group only, and this was significantly greater than values
for the MA group. CK values for the CON group remained
above baseline values at V4, V8, and at preexercise during
FIGURE 5—Testosterone responses (mean T SE) to the 12-wk resistance exercise intervention. Bars represent resting values; lines represent
responses to the AREP. *Significant difference from corresponding preexercise value, P e 0.05; †significant difference from corresponding V1 value,
P e 0.05; Lsignificant difference from corresponding control value, P e 0.05.
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FIGURE 6—Cortisol responses (mean T SE) to the 12-wk resistance exercise intervention. Bars represent resting values; lines represent responses to
the AREP. *Significant difference from corresponding preexercise value, P e 0.05; †significant difference from corresponding V1 value, P e 0.05;
Lsignificant difference from corresponding control value, P e 0.05.
than baseline values and corresponding values for the CON
group. Figure 11 displays the MDA values.
DISCUSSION
The prominent findings of the present investigation were
that 1) Muscle Armori supplementation potentiated gains
in lean body mass and muscle strength after 12 wk of
FIGURE 7—Growth hormone responses (mean T SE) to the 12-wk resistance exercise intervention. Bars represent resting values; lines represent
responses to the AREP. *Significant difference from corresponding preexercise value, P e 0.05; †significant difference from corresponding V1 value,
P e 0.05; Lsignificant difference from corresponding control value, P e 0.05.
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APPLIED SCIENCES
V9. Alternately, CK values for the MA group were below
baseline values at V5 and at preexercise during V6. During
the third AREP, CK values for the MA group were
significantly lower than the CON group at all time points.
Figure 10 displays the CK values.
MDA values increased during the first AREP, yet
returned to baseline and remained stable throughout V6.
Beginning at V7, MDA values for the MA group were less
APPLIED SCIENCES
FIGURE 8—Insulin-like growth factor-1 (IGF-1) responses (mean T SE) to the 12-wk resistance exercise intervention. Bars represent resting values;
lines represent responses to the AREP. *Significant difference from corresponding preexercise value, P e 0.05; †significant difference from
corresponding V1 value, P e 0.05; Lsignificant difference from corresponding control value, P e 0.05.
periodized resistance training; and 2) these adaptations were
potentially mediated, in part, by accentuated hormonal
responses and/or attenuated muscle damage. Overall, these
results indicate that supplementation with a blend of HMB and
conditionally essential amino acids (arginine, glutamine) and
taurine promote adaptations to resistance exercise training.
Resistance exercise training increased total and lean body
mass and decreased percent body fat; these improvements
in body composition were potentiated by MA supplementation. This may be explained by a greater availability of
extracellular amino acids in the MA group, which would
promote protein synthesis (4,5). Essential amino acids,
particularly leucine, stimulate muscle anabolism by activating the mammalian target of rapamycin (mTOR) and
subsequently p70S6K (3,16,27), and this has been shown
in model systems for HMB as well (10,39). Alternately,
FIGURE 9—Insulin responses (mean T SE) to the 12-wk resistance exercise intervention. Bars represent resting values; lines represent responses to
the AREP. *Significant difference from corresponding preexercise value, P e 0.05; †significant difference from corresponding V1 value, P e 0.05;
Lsignificant difference from corresponding control value, P e 0.05.
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Official Journal of the American College of Sports Medicine
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FIGURE 10—CK responses (mean T SE) to the 12-wk resistance exercise intervention. Bars represent resting values; lines represent responses to the
AREP. *Significant difference from corresponding preexercise value, P e 0.05; †significant difference from corresponding V1 value, P e 0.05;
Lsignificant difference from corresponding control value, P e 0.05.
with several previous studies that demonstrated HMB
supplementation, in conjunction with resistance exercise,
improved muscle mass, body composition % fat and
strength, and vertical jump power (28,29,31,38). Little is
known concerning the adaptations of tendon in response to
heavy resistance training. The findings of this study indicate
that the patella tendon thickness does increase after heavy,
periodized resistance training, although there were no
between-group differences. Currently, only one other study
FIGURE 11—Malondialdehyde responses (mean T SE) to the 12-wk resistance exercise intervention. Bars represent resting values; lines represent
responses to the AREP. *Significant difference from corresponding preexercise value, P e 0.05; †significant difference from corresponding V1 value,
P e 0.05; Lsignificant difference from corresponding control value, P e 0.05.
PROTEIN SUPPLEMENTATION AND STRENGTH TRAINING
Medicine & Science in Sports & Exercised
1119
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APPLIED SCIENCES
MA might have improved body composition because of the
anticatabolic properties of its ingredients: exercise-induced
proteolysis is reduced by HMB (28,34), arginine (26), and
glutamine (1,9). Gains in lean body mass were concomitant
with muscle strength improvements. Bench press and squat
1-RM were increased in both groups after 12 wk of training.
However, the increases in 1-RM bench press and squat
were significantly greater (P e 0.05) in the MA group
when compared with the CON group. Our findings agree
APPLIED SCIENCES
has directly reported patella tendon hypertrophy after heavy
resistance exercise (17).
Acute resistance exercise transiently increases circulating
concentrations of testosterone, cortisol, into hormone
sequence and GH (14), and nutritional consumption
modulates these responses (23). The influence of chronic
resistance exercise training on resting and exercise-induced
responses is less clear. In the present study, resting
testosterone was elevated after training commencement in
both groups. However, although the CON group had
increased resting testosterone only at V4 and V7, the MA
group showed increased resting testosterone at all time
points after V3. MA supplementation also potentiated
resistance exercise-induced testosterone responses during
the AREP at mid- and posttraining when compared with the
CON group. The importance of circulating testosterone for
promoting resistance exercise-induced adaptations as a
primary anabolic stimulus is clear. When endogenous
testosterone release is blocked (via a gonadotropin-releasing
hormone analog), strength and lean mass adaptations to
training are severely attenuated (24). Therefore, potentiation
of circulating testosterone might be an important mechanism by which MA supplementation promoted resistance
exercise adaptations.
Resting and exercise-induced cortisol concentrations
remained stable throughout the 12-wk intervention. Interestingly, though, preexercise cortisol concentrations were
reduced in the MA group immediately before the AREP at
mid- and posttraining. The mechanism for this response is
not entirely clear. Cortisol displays an anticipatory response
to impending intense exercise and competition (19,35), and
our laboratory previously demonstrated that this response
was attenuated using a specifically designed herbal supplement (19). Because supplementation with amino acids
increases the circulating amino acid concentrations (26),
possibly less cortisol was required to degrade proteins into
amino acids for gluconeogenesis before exercise. MA
supplementation also increased resting GH concentrations at
V8 and V9 above baseline and corresponding CON values.
Most studies have shown no change in resting GH concentrations with chronic training (15,22). However, the present
study is the first to use an HMB, arginine, glutamine, and
taurine supplement in conjunction with resistance training.
Reduced cortisol and increased GH at rest improves the
anabolic-to-catabolic hormone ratio, which, in theory, would
improve muscle tissue protein balance.
Resting CK values peaked at V2 and decreased with
progression of training; this was consistent with previous
studies showing that long-term resistance training reduced
CK concentrations after exercise (12,36). A possible
mechanism is that repeated bouts of resistance exercise
impart a protective effect on skeletal muscle, and therefore,
skeletal muscle is less susceptible to damage (25). Resting
CK values were significantly lower (P e 0.05) in the MA
group than that in CON group during training (V2 to V9).
Previous studies have shown that reduced protein degradation
is associated with a lower CK value (28,31) and that
supplementation with HMB (28) or branched chain amino
acids (9) can partially attenuate exercise-induced proteolysis
and/or muscle damage. Therefore, the findings of the present
study suggest that HMB supplementation attenuated muscle
damage during training and reduced protein degradation.
Consistent with prior research (37), the AREP increased
plasma MDA concentrations at pretraining. Yet, this
exercise challenge did not promote significant changes in
plasma MDA for either group at mid- and posttraining. At
posttraining, the MA group had significantly lower (P e
0.05) plasma MDA concentrations at preexercise and at 5
and 15 min into the recovery as compared with pretraining
and CON values. Because plasma MDA is a marker of free
radical formation and lipid peroxidation (27), which are
partly responsible for membrane disruption associated
with exercise, we conclude that MA was effective in attenuating muscle tissue disruption via reduced free radical
formation at rest and in response to the AREP. Prior
research has similarly shown that supplementation with
L-carnitine L-tartrate was effective in attenuating the plasma
MDA response to exercise (37).
In conclusion, 12 wk of periodized resistance training
increased lean body mass and muscle strength. In accord
with previous research, we demonstrated that concomitant
supplementation with HMB and conditionally essential
amino acids and taurine (the ingredients of Muscle Armori)
potentiated adaptations to resistance exercise training. Muscle Armori supplementation also improved anabolic hormonal responses, reduced preexercise catabolic hormonal
concentrations, and attenuated markers of muscle damage.
These results provide compelling evidence that long-term
supplementation with Muscle Armori promotes physical
and physiological adaptations to resistance exercise.
The authors thank a dedicated group of study subjects. The
authors also thank the personal trainers staff of certified strength
and conditioning specialists, laboratory technicians, and the dieticians who worked hard to make this study possible. This work
was supported by a grant from Abbott Laboratories (Abbott Park,
IL), the makers of Muscle Armori. The results of the present study
do not constitute endorsement by the American College of Sports
Medicine.
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