et encore un peu plus (+12%) avec de l'arginine AKG
Creatine, Arginine -Ketoglutarate, Amino Acids, and Medium-Chain Triglycerides
and Endurance and Performance
Jonathan. P. Little, Scott C. Forbes, Darren G. Candow, Stephen M. Cornish, and Philip D. Chilibeck
Creatine (Cr) supplementation increases muscle mass, strength, and power. Arginine
-ketoglutarate (A-AKG) is a precursor for nitric oxide production and has the potential
to improve blood flow and nutrient delivery (i.e., Cr) to muscles. This study compared
a commercial dietary supplement of Cr, A-AKG, glutamine, taurine, branchedchain
amino acids, and medium-chain triglycerides with Cr alone or placebo on
exercise performance and body composition. Thirty-five men (~23 yr) were randomized
to Cr + A-AKG (0.1 g · kg–1 · d–1 Cr + 0.075 g · kg–1 · d–1 A-AKG, n = 12), Cr
(0.1 g · kg–1 · d–1, n = 11), or placebo (1 g · kg–1 · d–1 sucrose, n = 12) for 10 d. Body
composition, muscle endurance (bench press), and peak and average power (Wingate
tests) were measured before and after supplementation. Bench-press repetitions over
3 sets increased with Cr + A-AKG (30.9 ± 6.6 → 34.9 ± 8.7 reps; p < .01) and Cr
(27.6 ± 5.9 → 31.0 ± 7.6 reps; p < .01), with no change for placebo (26.8 ± 5.0 → 27.1
± 6.3 reps). Peak power significantly increased in Cr + A-AKG (741 ± 112 → 794 ±
92 W; p < .01), with no changes in Cr (722 ± 138 → 730 ± 144 W) and placebo (696 ±
63 → 705 ± 77 W). There were no differences in average power between groups over
time. Only the Cr-only group increased total body mass (79.9 ± 13.0→81.1 ± 13.8 kg;
p < .01), with no significant changes in lean-tissue or fat mass. These results suggest
that Cr alone and in combination with A-AKG improves upper body muscle endurance,
and Cr + A-AKG supplementation improves peak power output on repeated
Wingate tests.
Keywords: exercise, power, ergogenic aids, athletic performance
Increasing dietary creatine (Cr) intake through supplementation improves
muscle performance in a single bout (Dawson et al., 1995; Earnest, Snell, Rodriguez,
Almada, & Mitchell, 1995; Volek et al., 1997) and repeated bouts of highintensity
exercise (Casey, Constantin-Teodosiu, Howell, Hultman, & Greenhaff,
1996; Dawson et al.; Greenhaff et al., 1993; Izquierdo, Ibanez, Gonzalez-Badillo,
& Gorostiaga, 2002; Kilduff et al., 2002; Okudan & Gokbel, 2005). The primary
Little, Forbes, Cornish, and Chilibeck are with the College of Kinesiology, University of Saskatchewan,
Saskatoon, SK, Canada. Candow is with the Faculty of Kinesiology and Health Studies, University of
Regina, Regina, Saskatchewan, Canada S4S OA2.
International Journal of Sport Nutrition and Exercise Metabolism, 2008, 18, 493-508
© 2008 Human Kinetics, Inc.
494 Little et al.
mechanism by which Cr supplementation improves muscle performance is thought
to be an increase in skeletal-muscle total Cr and phosphocreatine (PCr) content,
thus enhancing the ability to replenish adenosine triphosphate via the creatine
kinase reaction (Greenhaff, Bodin, Soderlund, & Hultman, 1994). Other possible
effects of increased total Cr and PCr content include accelerated resynthesis of
PCr during the recovery periods from repeated high-intensity exercise (Greenhaff
et al., 1994; Yquel, Arsac, Thiaudiere, Canioni, & Manier, 2002), increased
hydrogen-ion-buffering capacity (Greenhaff et al., 1993; Yquel et al.), and
increased net muscle protein synthesis leading to improved muscle mass (Ingwall,
Weiner, Morales, Davis, & Stockdale, 1974).
L-arginine is another supplement that has been reported to improve exercise
performance. The body of research on L-arginine and muscle performance is relatively
small, but supplementing with L-arginine and compounds containing it has
been shown to improve maximal strength (Campbell et al., 2006; Elam, Hardin,
Sutton, & Hagen, 1989), Wingate peak power (Campbell et al.), repeated sprint
performance (Buford & Koch, 2004), and fatigue resistance (Buford & Koch;
Stevens, Godfrey, Kaminski, & Braith, 2000). Although the mechanism by which
L-arginine supplementation enhances short-term exercise performance is not fully
known, L-arginine is required for endogenous synthesis of nitric oxide (Soeters,
Hallemeesch, Bruins, van Eijk, & Deutz, 2002), which functions to promote vasodilation
and increase blood flow. Increased blood flow could improve exercise
performance by facilitating nutrient delivery (i.e., creatine, glucose) or metabolic
waste-product removal from exercising skeletal muscle. Studies in healthy older
adults (Bode-Boger et al., 2003), patients with vascular disease (Kubota, Imaizumi,
Oyama, Ando, & Takeshita, 1997), and normotensive rats (Ohta, Takagi, Sato, &
Ignarro, 2007) have shown increased muscle blood flow after supplementing with
L-arginine.
Combining Cr and L-arginine supplementation is intriguing for two main
reasons. First, because both Cr and L-arginine supplementation appear to
improve muscle performance yet work by different proposed mechanisms, their
effects could be additive. Second, because L-arginine might enhance muscle
blood flow, combining L-arginine with Cr could increase the delivery of Cr to
skeletal muscle and increase the effectiveness of Cr supplementation. Coingesting
Cr with nutrients that stimulate insulin secretion, such as carbohydrates
(Green, Hultman, Macdonald, Sewell, & Greenhaff, 1996) or alpha-lipoic acid
(Burke, Chilibeck, Parise, Tarnopolsky, & Candow, 2003), and performing lowintensity
exercise after Cr ingestion to promote blood flow (Robinson, Sewell,
Hultman, & Greenhaff, 1999) have been shown to enhance muscle Cr retention,
demonstrating that skeletal-muscle Cr uptake can be manipulated. The primary
purpose of this study was to determine the effects of a commercial dietary supplement
containing Cr and L-arginine alphaketoglutarate (A-AKG; a modified
salt of L-arginine) as the main ingredients on muscle performance in young male
adults. Because both Cr (Kilduff et al., 2002) and A-AKG (Campbell et al.,
2006) supplementation have been shown to increase fat-free mass, we also
assessed changes in body composition. We hypothesized that Cr and A-AKG
supplementation would increase exercise performance and muscle mass compared
with Cr alone or placebo.
Creatine and A-AKG 495
The commercial Cr + A-AKG supplement (Xpand nitric oxide reactor,
Dymatize Enterprises Inc., TX) used in the current study also contained other ingredients
(e.g., branched-chain amino acids, medium-chain triglycerides, L-glutamine).
The available evidence and potential mechanisms supporting improved exercise
performance after short-term supplementation with these compounds is limited.
Therefore we assumed that the ingredients with ergogenic potential in the supplement
were Cr and A-AKG.
Methods
Participants
Thirty-seven healthy physically active men (22.8 ± 2.8 year) volunteered for the
study. They were participating in moderate physical activity ~2–3 times per
week and were instructed not to change their diet or physical activity patterns
before or during the study. All participants were required to fill out a Physical
Activity Readiness Questionnaire (PAR-Q), which screens for health problems
that might present a risk with performance of physical activity (Thomas, Reading,
& Shephard, 1992). The study was approved by the University of Saskatchewan
Biomedical Research Ethics Board for research in human participants. Participants
were informed of the risks and purposes of the study before written consent
was obtained. Participants had been free from other ergogenic aids for at
least 12 weeks before initial testing to eliminate any effects from other
supplementation.
Experimental Design
The study used a double-blind, repeated-measures design in which participants
were randomized to one of three supplement groups: Cr + A-AKG, Cr, or placebo.
Participants were required to visit the laboratory on two occasions before the start
of the study, once to determine their bench-press 1-repetition maximum (1-RM)
strength and again 3 days later for familiarization with the experimental protocol
by performing three sets of bench-press repetitions to fatigue (separated by 1-min
rest intervals) at an intensity corresponding to 70% 1-RM followed by three 30-s
Wingate cycle tests (separated by 2-min rest intervals) at a load corresponding to
0.075 kp/kg body mass. There was a 10-min rest period between the bench-press
endurance tests and Wingate cycle tests.
Approximately 3–7 days after the familiarization trial participants returned for
presupplementation testing. Body composition was measured by air-displacement
plethysmography (BodPod, Life Measurement Inc., Concord, CA) followed by
the same exercise protocol as during the familiarization session, except that fingerprick
blood lactate samples were taken (details below). Participants consumed the
supplement for 10 consecutive days before returning to the laboratory for posttesting.
The same testing protocol was repeated at this time. Participants were
instructed to refrain from caffeine for 48 hr, physical activity for 24 hr, and food
and drink for 3 hr before testing. The dependent variables measured before and
after 10 days of supplementation were (a) body mass, fat mass, and lean tissue
496 Little et al.
mass; (b) bench-press muscle endurance; (c) peak and average power during three
repeated Wingate tests; and (d) blood lactate concentration before, during, and
after the repeated Wingate tests. Side effects were determined by verbally prompting
participants on the posttesting day to indicate any side effects they had experienced
during the study. Participants were also told to report any side effects during
the study by contacting the investigators.
Supplementation
Participants were randomly assigned to one of three supplement groups: Cr +
A-AKG (0.1 g · kg–1 · day–1 Cr + 0.075 g · kg–1 · day–1 A-AKG, found in 0.35 g/kg
Xpand nitric oxide reactor), Cr (0.1 g · kg–1 · day–1 Dymatize Enterprises Inc.,
TX), or placebo (PLA, 1 g · kg–1 · day–1 sucrose-based fruit punch) for 10 days.
The Xpand supplement was mixed with 0.65 g/kg sucrose-based fruit punch, and
the Cr was mixed with 0.9 g/kg of the sucrose-based fruit punch to match the
supplements for caloric content, color, and taste. The supplements were separated
into 10 equal doses, and the participants were instructed to mix a single dose with
~1 L of water and consume half the serving 30 min before and the other half
30 min after a workout or, on nonworkout days, consume half the dose in the
morning and half in the evening. Ingredients in the Xpand supplement are shown
in Table 1.
Table 1 Ingredients in the Cr + A-AKG Supplement (Xpand Nitric
Oxide Reactor, Dymatize Enterprises, TX)
Ingredient
Daily supplement
amount (g/kg)
Tricreatine malate 0.1
Arginine alpha-ketoglutarate (A-AKG) 0.075
Betaine-anhydrous 0.05
Taurine 0.05
Glutamine-AKG, N-acetyl-L-glutamine 0.025
Vitamin B3 5 × 10-4
Vitamin B6 225 × 10-6
Folic Acid 22 × 10-7
Vitamin B12 9 × 10-7
Xpansion matrix: glycocyamine, glucuronolactone,
L-citrulline, medium-chain triglycerides, caffeine, aqueous
cinnamon extract, vinpocetine 99%, vincamine 99%, silicon
dioxide
1.0
Recovery matrix: BCAA complex (L-leucine, L-isoleucine,
L-valine), L-tyrosine, N-acetyl cysteine, L-phenalalaline,
vanadyl sulfate
0.052
Note. Ingredients are taken from the product label, and amounts are for the daily supplemental dose
given to participants expressed relative to body mass.
Creatine and A-AKG 497
Muscle Strength and Endurance
The procedures for determining bench-press 1-RM were previously described
(Candow, Burke, Smith-Palmer, & Burke, 2006). All bench-press testing was
performed on a plate-loaded machine (Lever chest-press machine, Winnipeg,
MB, Canada). Reproducibility of our 1-RM test, expressed as a coefficient of
variation was 1.9% (Candow, Chilibeck, Burke, Davison, & Smith-Palmer, 2001).
For bench-press muscle endurance, participants performed three sets of benchpress
repetitions to volitional fatigue, separated by 1-min rest intervals, at an
intensity corresponding to 70% 1-RM. Reproducibility of the bench-press endurance
test was assessed previously in our laboratory by testing 15 participants
3 days apart. The coefficient of variation was 1.5% (Forbes, Candow, Little,
Magnus, & Chilibeck, 2007).
Anaerobic Power
Peak and average power were assessed using repeated Wingate cycle-ergometer
tests. Blood lactate concentration was measured at rest, immediately after each
Wingate cycle test, and 2 min postexercise using an automated lactate analyzer
(Accutrend Lactate, Roche Diagnostics, Mannheim, Germany) according to the
manufacturer’s instructions. Ten minutes after the bench-press endurance test,
each participant was positioned on the Wingate cycle ergometer (Monark), and
seat height, handlebar height and position, and toe straps were adjusted based on
the settings determined during the familiarization trial. Participants were instructed
to cycle at a slow cadence (~50–60 rpm) against light resistance for 5 min. Five
seconds before data collection, participants were instructed to pedal at maximal
rate to ensure optimal power and force production at the beginning of the test and
to continue cycling at a maximal speed for the duration of the 30-s test at a load
corresponding to 7.5% of their body mass (Bar-Or, 1987). Participants were verbally
encouraged throughout the test. This procedure was repeated for three tests,
separated by 2 min of active rest against zero resistance between tests. Reproducibility
of peak and average power was determined previously in our laboratory by
testing 10 participants 3 days apart. The coefficients of variation were 4.1% for
peak power and 3.6% for average power (Forbes et al., 2007).
Dietary Intake and Physical Activity
Dietary intake (total calories, carbohydrates, protein, and fat) was determined by
having participants complete 3-day food diaries (2 weekdays and 1 weekend day)
at the start of the study. Food diaries were assessed by the USDA interactive eating
index (www.mypyramidtracker.gov). Physical activity levels were determined at
baseline by questionnaire (Godin & Shephard, 1985).
Statistical Analysis
A 3 (group; Cr + A-AKG vs. Cr vs. PLA) 3 (exercise sets) 2 (time; before
vs. after the 10-day supplementation period) ANOVA with repeated measures
on the last two factors was used to assess differences between conditions for
498 Little et al.
bench-press repetitions, as well as for peak power and average power during the
Wingate tests. A 3 (group) 5 (blood lactate at five time points) 2 (time)
ANOVA with repeated measures on the last two factors was used to assess
changes in blood lactate concentration. Body-composition measures were analyzed
with a 3 (group) 2 (time) ANOVA with repeated measures on the
second factor. Tukey’s post hoc tests were used to determine differences between
means when significance was found. Differences between groups for dietary
intake and physical activity levels were determined by a one-factor ANOVA.
Statistical significance was set at p ≤ .05. All results are expressed as M ± SD.
Statistical analyses were carried out using Statistica, version 7.0 (StatsSoft Inc.,
Tulsa, OK).
Results
Of the original 37 young men who volunteered, 35 participants (Cr + A-AKG n =
12; Cr n = 11; PLA n = 12) completed the study. Two withdrew because of time
constraints. There were no side effects reported from supplementation. There
were no differences between groups for average daily dietary intake (kcal: Cr +
A-AKG 3,067 ± 569; Cr 3,269 ± 699; PLA 2,775 ± 1026; carbohydrates: Cr +
A-AKG 351 ± 88 g; Cr 406 ± 74 g; PLA 332 ± 147 g; fat: Cr + A-AKG 105 ±
16 g; Cr 120 ± 38 g; PLA: 101 ± 35 g; protein: Cr + A-AKG 146 ± 44 g; Cr 139 ±
55 g; PLA 127 ± 45 g) or physical activity levels (physical activity scores in arbitrary
units: Cr + A-AKG 86 ± 32; Cr 89 ± 32; PLA 64 ± 18).
As expected, there was a significant set main effect for bench-press endurance
(p < .001); that is, performance dropped across sets. There was a significant
Group Time interaction (p < .05, Figure 1), with total bench-press repetitions
over three sets being significantly increased after supplementation in the Cr +
A-AKG (+4 ± 3.7 reps, or 12.4%) and Cr groups (+3.4 ± 3.2 reps, or 11.9%; p <
.01) but no change for placebo (+0.3 ± 2.4 reps, or 0.3%).
There was a significant set main effect for Wingate peak and average power
(both p < .001), with performance decreasing across sets as would be expected.
For peak power, there was a significant Group Time interaction (p < .05,
Figure 2). Peak power (average of the three Wingate tests) significantly increased
after supplementation in the Cr + A-AKG group (+54 ± 82 W, or +7.1%, p <
.05), with no differences in the Cr (–11 ± 47 W, or –1.5%) and PLA groups
(–9.4 ± 34.7 W, or –0.8%). There were no significant differences between supplement
groups for Wingate average power (Group Time interaction, p =
.089; Figure 3). Blood lactate concentration increased across sets during the
Wingate test (p < .01), but there were no differences between groups (data not
shown).
There were no significant differences between groups over time for lean-
tissue
mass or fat mass (Table 2). There was a significant Group Time interaction,
however, for body mass (p < .05), with post hoc tests revealing an increase
in body mass from pre- to postsupplementation in the Cr group only (p < .01,
Table 2).
499
Figure 1 — Bench-press repetitions over three sets in the Cr + A-AKG (A), Cr (B), and
placebo (C) groups before (pre) and after (post) 10 days of supplementation. Values are
M ± SD. *Significant increase in total number of bench-press repetitions from pre- to postsupplementation
(p < .01).
500
Figure 2 — Peak power output over three repeated Wingate cycling tests (separated by
2 min rest) in the Cr + A-AKG (A), Cr (B), and placebo (C) groups before (pre) and after
(post) 10 days of supplementation. Values are M ± SD. *Significant increase in peak power
from pre- to postsupplementation (p < .05).
501
Figure 3 — Average power output over three repeated Wingate cycling tests (separated by
2 min rest) in the Cr + A-AKG (A), Cr (B), and placebo (C) groups before (pre) and after
(post) 10 days of supplementation. Values are M ± SD.
502
Table 2 Body-Composition Measures (M ± SD) Before and After 10 Days of Supplementation
Cr + A-AKG Cr Placebo
Pre Post Pre Post Pre Post
Body mass (kg) 81.1 ± 9.3 81.5 ± 9.9 79.9 ± 13.0 81.1 ± 13.8* 78.9 ± 11.3 78.8 ± 13.7
Lean-tissue mass (kg) 68.4 ± 4.4 69.5 ± 4.6 66.6 ± 7.6 67.1 ± 8.2 65.1 ± 6.2 64.8 ± 5.8
Fat mass (kg) 12.5 ± 6.1 12.0 ± 6.6 13.2 ± 6.4 14.1 ± 6.4 13.8 ± 8.7 13.9 ± 9.0
% body fat 14.9 ± 5.7 14.1 ± 6.2 15.8 ± 5.8 16.8 ± 5.4 16.5 ± 7.4 16.5 ± 8.3
*Significant increase in body mass from pre- to postsupplementation.
Creatine and A-AKG 503
Discussion
The current study demonstrates that short-term supplementation with Cr (0.1 g ·
kg–1 · day–1) and Cr + A-AKG (0.1 + 0.075 g · kg–1 · day–1) can improve
high-intensity exercise performance. Ten days of both Cr and Cr + A-AKG supplementation
increased the total number of repetitions that could be performed
over three sets of repeated bench-press exercise. Only Cr + A-AKG supplementation,
however, induced significant performance improvements in peak power
during three repeated Wingate cycling tests. This provides preliminary evidence
that combining Cr with A-AKG might be superior to Cr supplementation alone for
power-type athletes.
Short-term Cr supplementation (5–10 days) has been shown to increase
high-intensity exercise performance over placebo (for review see Bemben &
Lamont, 2005). The mechanism behind the performance improvement is usually
attributed to an increase in intramuscular PCr stores, leading to an increased
capacity to replenish adenosine triphosphate through PCr hydrolysis. Although
we did not measure intramuscular PCr, the increased muscle endurance on the
repeated bench-press test was likely caused by an increase in PCr. PCr is an
important energy substrate for repeated resistance-training exercise (Lambert &
Flynn, 2002), so increased PCr availability after both Cr and Cr + A-AKG supplementation
could have enhanced total work capacity. Previous research has
reported an increase in the total number of bench-press repetitions performed at
a similar load (~70% 1-RM) after short-duration Cr supplementation (Earnest
et al., 1995; Volek et al., 1997). The lack of a significant difference between the
Cr and Cr + A-AKG groups for bench-press performance provides evidence
that the addition of A-AKG did not enhance skeletal-muscle Cr retention,
although a direct measurement of muscle Cr uptake would be needed to confirm
this. Alternatively, the high muscle tension and short duration of the benchpress
exercise might have negated any potential vasodilatory impact from
A-AKG supplementation.
The effects of Cr supplementation on Wingate cycle performance are mixed,
with some studies showing a positive effect (Okudan & Gokbel, 2005) and others
not observing the same benefits (Deutekom, Beltman, de Ruiter, de Koning, &
de Haan, 2000; Green, McLester, Smith, & Mansfield, 2001). For example,
Okudan and Gokbel reported that Cr supplementation (20 g/day for 6 days) in
untrained men led to improvements in peak power and total work output during
five repeated Wingate cycling tests. Our findings of no beneficial effect from Cr
on peak or average power support the findings of Deutekom et al. and Green et al.
(2001). Although it is difficult to compare results across studies, differences in
participant training status, dose and duration of Cr supplementation, and testing
methodology (i.e., number of repeated Wingate tests and duration of rest intervals)
might have influenced the results.
Despite no effect from Cr supplementation alone on repeated Wingate cycle
performance, we did find an increase in Wingate peak power after Cr + A-AKG
supplementation. This might suggest that A-AKG itself, or in synergism with Cr,
improves the ability to generate power on repeated Wingate tests. Our results support
the work of Campbell et al. (2006), who found a significant increase in
Wingate peak power in participants who supplemented with A-AKG (12 g/day)
504 Little et al.
during 8 weeks of resistance training. In addition, our results are the first to show
that adding A-AKG to Cr supplementation enhances high-intensity exercise performance
over Cr supplementation alone. L-arginine is required for endogenous
synthesis of nitric oxide (Soeters et al., 2002), which functions to promote local
vasodilation. Therefore, supplementing with A-AKG might enhance anaerobicexercise
performance by increasing localized blood flow (Ohta et al., 2007;
Paddon-Jones, Borsheim, & Wolfe, 2004), enhancing muscle glucose uptake
(McConell, Huynh, Lee-Young, Canny, & Wadley, 2006), or increasing lactate or
ammonia clearance (Schaefer et al., 2002). We did not find any differences
between groups for blood lactate concentration during the repeated Wingate tests;
however, the complex interplay between muscle lactate production and removal
might make this single measure difficult to interpret. The potential reasons for
which Cr + A-AKG supplementation was superior to Cr alone for improving
Wingate peak power but not bench-press performance are not entirely clear. Perhaps
the effects of L-arginine were more evident with the longer rest periods
between Wingate tests (2 min) than between bench-press sets (1 min). This might
have allowed for greater oxygen delivery and PCr resynthesis or enhanced removal
of metabolic inhibitors (e.g., H+, K+) during the recovery periods between
repeated Wingate tests. Further research is needed to determine the effects of
A-AKG (and related L-arginine compounds) on muscle blood flow and metabolism
during high-intensity exercise.
Similar to previous Cr supplementation studies (e.g., Deutekom et al., 2000;
Kilduff et al., 2004), we observed a small increase (~1.2 kg) in body mass after
supplementation in the Cr-only group. Ten days of supplementation is likely too
short to observe a meaningful increase in dry muscle mass. Therefore, the
increase in body mass after Cr supplementation is likely attributed to net bodywater
retention (Kilduff et al., 2004), because Cr can elevate intracellular osmolarity
and increase cellular hydration status (Balsom, Soderlund, Sjodin, &
Ekblom, 1995). For example, reduced 24-hr urine excretion has been reported
after acute Cr supplementation (Hultman, Soderlund, Timmons, Cederblad, &
Greenhaff, 1996), and Francaux and Poortmans (1999) observed a significant
increase in net water retention after 42 days of Cr supplementation and strength
training. Furthermore, we have previously observed an increase in total bodywater
content (extracellular and intracellular) from Cr supplementation in vegetarians
(Burke et al., 2003). It is not clear why we did not see similar increases
in body mass after supplementation in the Cr + A-AKG group. The improvements
in bench-press and Wingate performance would seem to indicate that Cr
supplementation was effective at increasing intramuscular PCr in the Cr +
A-AKG group. From Table 2, it can be seen that, on average, the Cr + A-AKG
group increased lean-tissue mass by ~1.1 kg yet decreased fat mass by ~0.5 kg.
Therefore, any increase in body mass might have been masked in the Cr +
A-AKG group by the decrease in fat mass.
It is important to note that the Xpand supplement containing Cr and A-AKG
also contained other ingredients (see Table 1). For example, it contained small
amounts of the branched-chain amino acids (BCAAs), medium-chain triglycerides
(MCTs), taurine, glutamine, and L-citrulline. BCAA and MCT supplementation
might be beneficial when consumed within the hours before or during endurancetype
exercise (see reviews by Blomstrand, 2006 and Jeukendrup & Aldred, 2004,
Creatine and A-AKG 505
respectively). Supplementation in the current study, however, occurred for 10 days,
and the exercise performed was of short duration. Therefore, it is unlikely that
BCAA or MCT ingestion would have an ergogenic affect. Chronic taurine administration
has been shown to enhance exercise time to exhaustion in rats (e.g.,
Miyazaki et al., 2004), but we are unaware of any human studies that support these
findings. Glutamine is an amino acid that has been shown to help prevent protein
degradation in clinical patients undergoing muscle wasting (Stehle et al., 1989),
but its efficacy for increasing muscle mass and exercise performance in healthy
individuals undergoing resistance training has not been supported (Candow et al.,
2001). L-citrulline is an amino acid that, once ingested, is converted to L-arginine
by the kidneys and other tissues, leading to an increase in plasma L-arginine
(Hickner et al., 2006). Therefore, any potential for L-citrulline to improve exercise
performance is likely through an L-arginine pathway (e.g., NO synthesis).
In conclusion, this is the first study to examine the combined effects of Cr and
an L-arginine-containing compound on exercise performance. Because of the similar
performance-enhancing effects of Cr and L-arginine supplementation (i.e.,
increased muscle strength and power, increased fatigue resistance during repeated
high-intensity exercise), we designed the current study in an attempt to determine
whether an L-arginine compound combined with Cr was superior to Cr supplementation
alone. Because there are many NO-enhancing products (containing
L-arginine) on the market today, it seems prudent to evaluate their effectiveness.
The current study adds to the growing body of literature that reports improved
resistance-training exercise performance after supplementing with Cr. This was
demonstrated by an ~12% improvement in the number of repetitions performed on
three repeated sets of bench press at 70% 1-RM after supplementation with both
Cr and Cr + A-AKG. Ten days of supplementing with Cr + A-AKG, but not Cr
alone, improved peak power on three repeated Wingate cycling tests. These results
suggest that combining Cr with A-AKG might confer a further exercise performance
advantage compared with Cr alone. These results have immediate application
for athletes and exercising individuals involved in power-type events. Further
research is required to determine the mechanisms by which A-AKG and other
L-arginine-containing compounds (alone and in combination with Cr) improve
high-intensity-exercise performance. In addition, future training studies are needed
to determine whether the extra performance improvements seen with Cr + A-AKG
supplementation result in enhanced adaptations to a training program.
Acknowledgments
Nutritional supplements were donated by Peak Performance Inc., Ontario, Canada.
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