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Role of Amino Acid Ingestion in Protein Synthesis, Muscular Recovery and Adaptation to
Exercise Training
Introduction
Exercise training is performed with the intent to increase the capacity of muscular tissue to
perform work. The specific capabilities that can be enhanced by training include absolute, rate,
and duration of force production. These capabilities are supported by size and number of
contractile elements of muscle fiber, the mitochondrial structures that support energy production,
and increases in metabolites that contribute to these systems. Ikegawa, Funato, Tsunoda,
Kanehisa, Fukunaga, and Kawakami (2008) report that the ability for skeletal muscle to produce
force is related to its cross-sectional area and fiber size. Blazevich, Coleman, Horne, and
Cannavan (2009) further conclude that with increasing muscle volume and cross-sectional area
there is greater potential for skeletal muscle to produce force. Muscle protein synthesis is the
mechanism for increases in muscle fiber size and muscle cross-sectional area. As reported by
Phillips (2004) and Wilkinson, et al. (2008), muscle contractions that occur during exercise
training produce increases in protein breakdown with a simultaneous increase in signaling for
muscle protein synthesis. Kumar, Atherton, Smith, and Rennie (2009) identified that net protein
balance is negative after exercise until amino acids are ingested, while Tipton, Ferrando, Phillips,
Doyle, and Wolfe (1999) found that specifically the essential amino acids (EAA) must be
provided in order for the synthesis of new proteins to occur. Therefore, when exercise training is
accompanied by the sufficient supply of EAA there is an increase in muscle fiber size that leads
to increases in the capacity for muscle to produce force (Tipton et al., 1999, Kumar et al. 2009,
and Blazevich et al. (2009).
In agreement with Wilkinson et al. (2008) and Kumar et al. (2009), Millward, Bowtell, Pacy, and
Rennie (1994) and Blomstrand and Saltin (1999) identified that individuals engaged in regular
exercise have protein requirements in excess of the Recommended Daily Allowance (RDA) for
protein in sedentary people (.8g/kg bodyweight) because of the protein breakdown that occurs
during exercise. Furthermore, Tarnopolsky (2004), Tarnopolsky, Atkinson, MacDougall,
Chesley, Phillips, and Schwarcz (1992), and Lemon (1995) suggest that the daily protein
requirement for weightlifters and athletes engaged in strength training is 1.4-1.8g/kg bodyweight
per day and 1.2-1.4g/kg bodyweight for endurance athletes. Campbell et al. (2007) suggest that
individuals engaged in regular exercise training require more dietary protein than sedentary
individuals and protein intakes of 1.4–2.0 g/kg/day are not only safe, but may improve the
adaptations to exercise training.
Competitive athletes commonly manipulate dietary intake and utilize dietary supplements to
facilitate recovery and performance during training and competition. According to Applegate and
Grivetti (1997) amino acid and protein supplements have been used by recreational and
competitive athletes since the 1950s. As identified by Froiland, Koszewski, Hingst, and Kopecky
(2004), Maughan, DePiesse, and Geyer (2007) and Petroczi and Naughton (2007), dietary
supplement use among athletes is becoming more prevalent as a means of enhancing muscle
proteins synthesis, recovery, and adaptation to the training stimulus. Campbell et al. (2007),
Tang and Phillips (2009), and Wolf (2002) suggest that it is not always practical for athletes to
rely on food alone to meet their nutritional requirements due to length of competitions and
practices and preparation requirements. Protein and amino acid supplements require little
preparation and have a faster digestion and absorption rate than whole foods that may contribute
to enhanced recovery and exercise performance when consumed surrounding exercise (Campbell
et al. 2007).
The identification of the role of amino acids in muscle protein synthesis, recovery from exercise,
and improved performance will provide a basis for recommending appropriate amino acid
supplement protocols. Identifying the specific amino acids required, pattern of ingestion and
dosage to enhance protein synthesis and muscular recovery will provide individuals engaged in
exercise training with a safe and effective means to ensure they maximize the benefits from their
training.
Review of Literature
According to Bolster, Jefferson, and Kimball (2004), protein synthesis following exercise is a
result of short-term responses in intracellular signaling during and in the hours following
exercise and longer-term changes in mRNA translation. Human skeletal muscle is composed of
essential amino acids (EAA) as well as non-essential amino acids (NEAA) that the body can
synthesize from the EAAs. According to Mero (1999) only .5-1% of the body’s amino acids are
available for metabolic processes and the circulating amino acid levels change acutely in
response to food intake and exercise. Kumar et al. (2009) determined that a net gain in muscle
protein in response to exercise occurs only when amino acids are provided and protein synthesis
is delayed until amino acids are ingested. As discussed by Mero (1999), the EAA including the
branched-chain amino acids (BCAA) leucine, valine, and isoleucine, must be obtained through
diet because human cells do not possess the enzymes to synthesize these amino acids. Ingestion
of EAA, particularly the BCAA, produces phosphorylation of proteins through the target of
rapamycin signaling pathway (mTOR) whose activation is required for protein synthesis to take
place. West et al. (2011) identified that a rapid rate of appearance of amino acids in the blood as
occurs following ingestion of amino acid supplements provides greater stimulation of mTOR and
protein synthesis than slower rates of appearance that are seen following whole food
consumption. Tipton, Elliott, Cree, Aarsland, Sanford, and Wolfe (2007), Hoffman, Ratamess,
Tranchina, Rashti, Kang, and Faigenbaum (2009), and Cribb & Hayes (2006) report that protein
synthesis in response to amino acids is greatest when consumed prior to or during the exercise
session. Considering these effects of amino acid availability within the body it can be suggested
that the provision of external sources of EAA and BCAA during the critical time period surround
exercise is necessary to prevent muscle protein breakdown, produce new muscle synthesis, and
facilitate muscular recovery and adaptation to the exercise stimulus.
EAA/BCAA and Cellular Signaling
Based on their observation that disruption of the kinases targeted by the mTOR pathway results
in decreased muscle growth, Ge et al. (2009) suggest that mTOR regulates muscle regeneration
through kinase-independent and kinase-dependent mechanisms at the early stages of myofiber
formation and myofiber growth. These authors concluded that activation of mTOR is not only
permissive, but required for the myotube maturation phase and initiates the myoblast
differentiation phase of protein synthesis. According to Drummond, Dreyer, Fry, Glynn, and
Rasmussen (2009), the regulation of skeletal muscle protein synthesis involves interactions of
gene transcription, gene translation and protein breakdown. One of the required steps for protein
synthesis, translation initiation, involves a series of events necessary for ribosomal complex
assembly and binding of the target messenger RNA. Drummond et al. (2009) and Ge et al.
(2009) suggest that because mTOR regulates phosphorylation of kinases involved in the
translation and initiation phases of protein synthesis and is influenced by nutrient availability,
hormone activity, and muscle contraction, it is therefore a critical regulator of protein synthesis.
According to Atherton et al. (2010), the role for BCAA and EAA in protein synthesis is two-part
in that their presence in circulation enhances mTOR activity and also provides substrate for the
synthetic process. As a means of determining the roles of exercise and amino acid ingestion in
the activation of protein synthesis, Karlsson, Nilsson, Nilsson, Chibalin, Zierath, and Blomstrand
(2004) evaluated the independent and combined effects of one session of resistance training (4
sets of 10 repetitions of leg press at 80% of one repetition maximum (1RM)) and BCAA
ingestion on the activation of the mTOR complex. These investigators found that while one
session of resistance exercise alone increased activation of mTOR, phosphorylation at several
sites was unchanged and therefore was not sufficient to maximally activate mTOR. However, the
continuous ingestion of 100mg/kg bodyweight BCAA (~7.44 ± .35g total BCAA per subject)
prior to and throughout the exercise session significantly increased mTOR activity (p < 0.05) at
those sites activated by exercise alone while also activating sites not affected by exercise. Dreyer
et al. (2008) observed that ingestion of .5g/kg lean mass sucrose and .35g/kg lean mass EAA
(.186g/kg lean mass BCAA) one hour after exercise (10 sets of 10 repetitions of leg extensions at
70% 1RM) produced a significant five-fold increase in mTOR phosphorylation compared to a
two-fold increase observed during exercise alone (p < 0.05). The increased mTOR activation
following ingestion of the amino acid and carbohydrate supplement was accompanied by a 145%
increase in mixed muscle protein synthesis compared with a 41% increase observed in those
subjects performing resistance exercise without ingestion of amino acids (Dreyer et al. 2008).
Compared to exercise alone, BCAA ingestion following exercise produced increased activation
of the cellular signaling mechanisms involved in protein synthesis along with greater protein
synthesis (Dreyer et al. 2008). Moore et al. (2009) identified no effect of 20g intact-protein
(providing ~8.6g EAA) on the mTOR signaling complex. Campbell et al. (2007), West et al.
(2011), and Tang and Phillips (2009) suggest that differences in metabolism between intact
protein and amino acid supplements including requirement for enzymatic breakdown and
resulting slower rate of appearance of amino acids in circulation following complete protein
ingestion may reduce the capability for intact, complete proteins to activate mTOR and achieve
maximal protein synthesis as compared to EAA and BCAA ingestion.
The BCAA and leucine in particular, may have greater effects on mTOR activation than other
amino acids. In their review of the effects of supplementation with the BCAA leucine, Balage
and Dardevet (2010) concluded that in addition to serving as a substrate for protein synthesis,
leucine functions as a nutrient signal regulating protein metabolism through activation of cellular
signaling pathways including mTOR. Pasiakos et al. (2011) compared the effects of ingestion of
10g of EAA with varying proportions of leucine during a single bout of exercise on protein
metabolism and intracellular signaling throughout 13 days following the exercise-
supplementation protocol. The authors provided 10 recreationally fit subjects (VO2 peak: 40-
50L/kg/min) with either a leucine-enriched supplement containing 3.5g leucine or a supplement
containing 1.87g leucine during a 60 minute bout of moderate steady state cycling exercise (60 ±
5% VO2 peak). Subjects consuming the leucine-enriched supplement experienced 33% (p < 0.05)
greater post-exercise muscle protein synthesis (0.08 ± 0.01% per hour) than those consuming the
standard EAA supplement (0.06 ± 0.01% per hour). Net protein balance, the sum of muscle
protein breakdown and muscle protein synthesis, was positive but not different (p < 0.05)
between the two groups. Together, these results support an advantage to consumption of BCAAs,
particularly leucine, in greater amounts than other amino acids for maximization of cellular
signaling of protein synthesis.
The Requirement for Ingestion of BCAA vs. Leucine Alone/
Differential Requirements for Exogenous EAA, BCAA, and NEAA for Protein Synthesis
Balage and Dardevet (2010) identified a paradoxical interaction between the BCAAs such that
leucine consumption induces a decrease in both valine and isoleucine concentrations that is
immediately apparent when leucine is administered with a meal. Balage and Dardevet (2010)
suggest that leucine supplementation should be accompanied by valine and isoleucine to avoid
imbalanced BCAA levels that reduce the availability of valine and isoleucine as substrates and
limit the capacity to synthesize new proteins. Through their work, Bohé, Low, Wolfe and Rennie
(2003) and Kurpad, Regan, Raj, and Gnanou (2006) confirmed the requirement for the presence
of all three BCAA, as well as to a lesser extent all of the EAA, through their findings that
consumption of leucine alone produced decreased concentration of all other amino acids, thereby
limiting the amount of substrate available for protein synthesis. Additionally, Pasiakos et al.
(2011) observed that post-exercise plasma isoleucine (57 ±7 lmol/L) and valine (247 ± 17
lmol/L) concentrations were lower in those who consumed 10g of a leucine-enriched EAA
supplement containing 3.5g leucine than in those who consumed 10g of EAA containing 1.87g
leucine (79 ± 8 and 278 ± 17 lmol/L, isoleucine and valine, respectively). Therefore, while
ingestion of leucine by itself stimulates the protein synthetic process, there is a greater degree of
protein synthesis when all three BCAA are ingested compared to ingestion of leucine alone.
Although the BCAA group of the EAA have a recognized role in stimulating synthesis and
maximizing intracellular signaling, researchers have identified an inability for BCAA ingestion
alone to produce maximal protein synthesis in response to exercise due to the absence of the
complete compliment of amino acids present in human skeletal muscle. Kraemer et al. (2009)
report that the mRNA translation step of protein synthesis cannot proceed without the
availability all 20 amino acids present in human skeletal muscle. However, 11 of the 20 amino
acids present in human muscle are considered non essential because the body can synthesize
them, whereas the remaining nine EAA must obtained through diet (Wu 2010). Tipton et al.
(1999) identified that NEAA are not required for protein synthesis to occur and that consumption
of EAA are solely responsible for protein synthesis following exercise. Tipton et al. (1999)
compared the effects of post-resistance exercise consumption of three amino acid supplements
on amino acid metabolism and protein turnover in six volunteers. The supplement beverages
consisted of 1) 40g mixed amino acids containing 17.96g EAA (8.9g BCAA) and 22.04g NEAA,
2) 40g EAA + arginine, containing 34.5g EAA (16.6g BCAA) and 5.5g arginine, and 3) a non-
caloric placebo. Net protein balance was negative for the placebo condition, but improved from
negative (-50 ± 23 nmol·min-1 ·100 ml leg volume-1) to positive during mixed amino acid
ingestion (17 ± 13 nmol·min-1 ·100 ml leg volume, p < 0.05) with further improvement observed
with the greater EAA ingestion (29 ± 14nmol·min-1 ·100 ml leg volume-1; p < 0.01).
Miller, Tipton, Wolf, and Wolfe (2003) compared the effects of ingestion of three different
supplements containing 1) 35g of carbohydrate with 6g of amino acids (3g EAA + 3g NEAA), 2)
35g of carbohydrate only, and 3) 6g of the EAA+NEAA mixture only on muscle protein
synthesis after resistance exercise. They observed that the addition of 35g carbohydrate to 6g of
mixed amino acids did not produce greater stimulation of net muscle protein synthesis than the
amino acids alone. In a similar study, Borsheim, Tipton, Wolf, and Wolf (2002) provided
subjects with 6g EAA at one hour and again at two hours following leg press (10 sets of 10
repetitions) and leg extensions (8 sets of 8 repetitions) at 80% 1RM. When Borsheim et al.
(2002) compared their results to those of Miller et al. (2003) these authors identified that the
replacement of 3g NEAA with 3g EAA (6g total) in the EAA + carbohydrate mixture resulted in
an approximately 2-fold greater net protein balance. Borsheim et al. (2002) also reported that
following the first dose of 6g EAA muscle protein balance increased proportionally more than
arterial amino acid concentrations and returned rapidly to basal values when amino acid
concentrations decreased and increased again with provision of the second dose of 6g EAA.
Together the results of the work by Borsheim et al. (2002) and Miller et al. (2003) support the
dependence of protein synthesis on total EAA intake because consumption of 3g EAA resulted in
less protein synthesis than 6g EAA and a further increase was observed with administration of a
second 6g dose of EAA. In total, these findings of Kraemer et al. (2009), Tipton et al. (1999),
Borsheim et al. (2002), and Miller et al. (2003) along with the identification by Kumar et al.
(2009) that net protein balance is negative after exercise until amino acids are ingested, lead to
the conclusion that in order for maximal protein synthesis to occur in response to exercise, the
EAA must be ingested from exogenous sources in adequate amounts within the period of
elevated intracellular signaling during and following exercise, while the provision of NEAA
provides no benefits over the EAA alone.
Dose-Dependent Effects of EAA/BCAA Intake
Cuthbertson et al. (2005) and Glynn et al. (2010) observed that under conditions of rest without
exercise, myofibrillar and sarcoplasmic protein synthesis increase in a dose-dependent fashion
following ingestion of doses of 2.5-10g of EAA, with no further stimulation achieved with a
dose of 20 grams EAA. Moore et al. (2009) observed that muscle protein synthesis increased in a
dose-dependent manner and peaked at ~93% (p < 0.01) over fasting with consumption of a 20g
dose of complete protein equivalent to ~8.6g EAA following leg resistance exercise (4 sets each
of leg press, knee extension, and leg curl using a load that produced failure within 8–10
repetitions). Moore et al. (2009) observed no difference in protein synthesis between doses of 20
and 40g protein (p = 0.29). Leucine oxidation was stimulated following ingestion of 20g and 40g
protein indicating amino acids were available in excess of the requirements for protein synthesis
(Moore et al. 2009). Similarly, Kumar et al. (2009) observed that ingestion of 20g of complete
protein providing all of the EAAs was sufficient for achieving the greatest degree of protein
synthesis following exercise because ingestion of additional protein provided no further benefit.
However, Tipton et al. (1999) identified that ingestion of 34.5g EAA (16.6g BCAA) or 17.96g
EAA (8.9g BCAA) produced significantly greater post-exercise protein synthesis (p < 0.05)
compared to a non-caloric placebo, with the greater increase observed in the group consuming
34.5g EAA. Given that the addition of BCAA to exercise maximally stimulates mTOR signaling
it is possible that addition of BCAA to the amounts of EAA identified to maximize protein
synthesis (~10 grams EAA at rest and between 17.96g and 34.5g EAA or more during exercise)
may increase the amount of protein synthesized (Karlsson et al. 2004, Cuthbertson et al. 2005,
Glynn et al. 2010 and Tipton et al. 1999). In turn, there may be a greater requirement for the
EAA to serve as substrate to compliment the enhanced signaling produced by the BCAA (Tipton
et al. 1999, & Cuthbertson et al. 2005).
Timing of EAA/BCAA Ingestion, Delivery to Muscle and Subsequent Incorporation into Protein
An ideal property of EAA and BCAA supplements is the ability to time ingestion around
exercise to provide peak concentrations of amino acids in the blood when the contraction-
induced signaling and potential for delivery of amino acids and subsequent incorporation into
muscle protein is greatest (Tipton et al. 2007, Hoffman et al. 2009, and Cribb & Hayes 2006).
Shimomura et al. (2006) found that a 5g mixture of BCAA produced elevated plasma
concentrations of the BCAA within 15 minutes and reached peak values 30 minutes after
ingestion. Nosaka, Sacco, and Mawatari (2006) identified that following doses of 3.6g and 7.2g
of the EAA + four NEAA administered prior to exercise, blood levels of the BCAA increased 30
minutes after ingestion and these values remained elevated over placebo at all time points
through 24 hours post-exercise.
Support for the ingestion of amino acids prior to and during exercise as opposed to following
exercise is provided by Tipton et al. (2001) and their observation that delivery to and uptake of
EAA to working muscle was significantly greater (p < 0.05) when consumed immediately
preceding resistance exercise as compared to immediately following exercise. In their study, six
healthy human subjects participated in two trials on separate occasions during which they
ingested a supplement containing 6g of EAA (comprised of 2.4g BCAA) and 35g sucrose
immediately before or immediately after leg resistance exercise performed at 80% of 1RM (10
sets of 8 repetitions of leg press and 8 sets of 8 repetitions of leg extension). The delivery of
amino acids to the working musculature during exercise was increased by 650% with pre-
exercise ingestion of the supplement and 250% with post-exercise ingestion. Furthermore,
phenylalanine uptake, an indicator of muscle protein synthesis, greater (p = 0.0002) when
ingested before exercise (209 ± 42 mg) compared to ingestion following exercise (81 ± 19mg).
Borsheim et al. (2002) identified that consumption of 6g of EAA following exercise had no
effect on muscle protein breakdown and determined that the improvement in net muscle protein
balance they observed was the result of increased protein synthesis. Pasiakos et al. (2011)
reported that ingestion of 10g of EAA containing 3.5g leucine during exercise reduced muscle
protein breakdown by ~20% (p < 0.05) compared to 10g EAA containing 1.87g leucine.
Compared to exercise alone and ingestion following exercise, consumption of EAA/BCAA prior
to and during exercise suppresses protein breakdown and increases mTOR signaling which
produces greater net protein balance (Borsheim et al. 2002, Pasiakos et al. 2011, & Tipton et al.
2001).
EAA and BCAA Ingestion and Increased Muscle Mass
Vieillevoye, Poortmans, Duchateau, and Carpentier (2010) compared the effects of consumption
of two servings per day of either a placebo (30g saccharose carbohydrate) or supplement of 15g
EAA (containing 6.1g of BCAA) + 15g of saccharose on adaptations to a 12-week whole body
strength training program in 29 healthy males. Each supplement was consumed with breakfast
and dinner on the non-exercise days and with breakfast and immediately after the training
session on the exercise days. Twice per-week subjects performed resistance exercise consisting
of bench press, leg press, calf press, high lift, and leg curl exercises at 70-85% of 1RM and
totaling 36-50 repetitions per exercise. The authors determined that the daily protein intake of the
subjects was adequate to achieve positive net protein balance and therefore not limiting in regard
to muscle protein synthesis. Both placebo (p < 0.01) and EAA (p < 0.001) groups increased total
muscle mass during the 12 week period. The EAA group increased muscle mass by 3.3 ± 2.6%
(from 33.0 ± 3.1 to 34.1 ± 3.2 kg), while the placebo group increased muscle mass by 2.3 ± 2.2%
(from 34.9 ± 3.6 to 35.7 ±3.5 kg). Over the course of the study there was an increase in whole
body muscle mass of 1.1kg for the EAA group and 0.8kg for the placebo group. Furthermore, the
authors observed significant changes in muscle architecture of the EAA group only, who
experienced an increase in fiber thickness (from 20.3 ± 2.0 to 21.1 ± 2.1mm (3.8 ± 2.8%, p <
0.01) and pennation angle (5.6%, p < 0.05) of the gastrocnemius medialis. Ispoglou, King,
Polman, and Zanker (2011) evaluated the effects of daily ingestion of 4g of leucine during a
twice per week, 12-week resistance training program. The resistance training included leg press,
bench press, chest cross, pullover, overhead press, preacher curls, triceps press, and prone leg
curl. The first weekly session employed 3 sets of 10 repetitions at a training load adjusted to
produce failure at the tenth repetition in the final set for each exercise. The second weekly
session was comprised of 4 sets of 5 repetitions at each subject’s predetermined 5RM for each
exercise. The authors observed that 4g per day of leucine produced measurably greater gains in
lean mass (1.53 kg (±1.3 vs. 1.08 kg (±1.1)) and losses in fat mass (0.93 kg (±3.0) vs. 0.41 kg
(±1.4) than placebo, though the difference between the groups was not statistically significant
(lean mass, p = 0.36 and fat mass, p = 0.92).
Effects of EAA and BCAA During Overreaching, Under-recovery and Caloric-Restriction
In addition to the cellular signaling and protein synthetic responses to ingestion of amino acids
previously discussed, there is research to support the use of EAA and/or BCAA supplementation
to prevent or decrease the reductions in performance typically observed during periods of
overreaching training and under-recovery, as well as preservation of muscle mass during
conditions of caloric restriction (Ratamess et al. 2003). Prevention of reductions in performance
and muscle mass are particularly important to the competitive athlete who must perform at high
levels year-round as training programs typically incorporate periods of high volume training,
high-intensity training, or a combination of the two in order to evoke a rebound adaptation
during the subsequent period of decreased volume and intensity. According to Ratamess et al.
(2003), recovery from consecutive total-body workouts is critical to performance, especially
when overreaching is performed with the goal of enhancing performance due to a rebound effect.
A common response to overreaching and high-volume, high-intensity training programs with
insufficient recovery is increased activity of catabolic hormones and markers of muscle damage
along with decreased activity of anabolic hormones. Sharp and Pearson (2010) found that the
daily ingestion of 3g of mixed amino acids (containing 1.65g of BCAA) at the morning and
evening meals significantly decreased the cortisol response on the second day (p = 0.011), third
day (p = 0.005) and 36 hours after the final training session (p = 0.022) during four days of
overreaching resistance training performed over a period of seven days. Each exercise session
consisted of three sets of 6–8 repetitions at 80% of 1RM of leg press, leg curl, leg extension,
chest press, military press, latissimus pulldown, dumbbell curl, and triceps pushdown. Total area
under the curve for serum cortisol compared to baseline was significantly lower (p < 0.001) for
BCAA compared to the placebo condition. In addition to the reductions in the catabolic hormone
cortisol, the authors identified that total serum testosterone levels, measured as area under the
curve, were significantly greater (p < 0.001) with BCAA supplementation compared to placebo.
Similarly, Kraemer et al. (2006) observed that during the four week overreaching phase of a
resistance training program, subjects ingesting .4g/kg day amino acids (.218g/kg BCAA) had
significantly higher values for resting serum testosterone compared with the placebo group
during weeks 2,3, & 4 (p < 0.05). Further supporting a role for BCAA in reducing catabolism
and maintaining anabolic activity during overreaching exercise, Kraemer et al. (2006) reported
that creatine kinase, a marker of muscle damage, was significantly decreased (p = 0.004)
compared to placebo after the final training session. The observed decreases in creatine kinase
were inversely correlated (r = -0.67, r2 = 0.45) to 1RM squat performance and therefore BCAA
ingestion may prevent muscle damage and corresponding reductions in strength (Kraemer et al.
2006).
Along with the observed reductions in catabolic hormones and markers of muscle damage,
investigators have observed a positive impact on recovery of strength performance in the days
following exercise-induced muscular damage. Sugita, Ohtani M, Ishii, Maruyama, and
Kobayashi (2003) provided a 5.6g mixture of amino acids containing 1.7g of BCAA twice daily
each of the 10 days after a bout of eccentric elbow flexion/extension exercise. These authors
reported that compared to the placebo group, subjects consuming the amino acid supplement
displayed attenuations in reductions in measures of strength on the second and third day after the
exercise condition. The maximum isometric strength in the subjects consuming the amino acids
showed a significantly smaller decline (p = 0.05) relative to the placebo group on days 2, 3, and
6 following exercise. Additionally, most of the subjects receiving the amino acid mixture
reported less delayed muscle soreness compared to the placebo group.
In their study Ratamess et al. (2003) evaluated the effects of amino acid supplementation in 17
resistance-trained men during a four week period of high volume overreaching total-body
resistance training performed on consecutive days to minimize recovery between workouts.
During the first overreaching phase (weeks 1 and 2) the resistance training consisted of 8
exercises using a load equal to each subject’s 8-12RM for 3 sets performed to failure. In the
second overreaching phase (weeks 3 and 4) subjects performed 5 sets to failure for 5 exercises at
a load equivalent to their 3-5RM. Subjects in the placebo group ingested capsules of cellulose
powder, while the amino acid group ingested a total of 0.4 g/kg body weight mixed amino acids
(providing .218g/kg bodyweight BCAA) per day divided into three daily doses consumed one
hour before a meal, and two hours following a meal. Ratamess et al. (2006) identified that
consumption of the amino acid supplement attenuated the decline in 1-repetition max (1RM)
squat and bench press performance (-5.2kg and -3.4kg, respectively) that occurred in the placebo
group during the 2nd week of the study. Both groups displayed significant increases in 1RM squat
and bench press (p < 0.05) during weeks 3-5 of the study, with a significantly greater overall
improvement (p < 0.05) achieved in the amino acid group (from 130.8 ± 33.5kg to 142 ± 36kg
for the squat in the supplement group; 135.1 ± 20.4kg to 143.0 ± 21.5kg placebo; and 108.6 ±
17.6kg to 116.7 ± 17.8kg for the bench press in the supplement group, 110.5 ± 15.6kg to 116.8 ±
17.1kg placebo). Amino acid supplementation also maintained peak power performance in the
ballistic bench press and jump squat at week 3, whereas a significant reduction (p < 0.05) in the
ballistic bench press was observed in the placebo group. In addition, only the amino acid group
showed a significant increase (p < 0.05) at week 5 in the jump squat (146 vs. 98 watts,
respectively, in supplement and placebo) and a trend (p = 0.08) for increase at week 5 in the
ballistic bench press (40 vs. 20 watts, respectively, for supplement and placebo).
In addition to the physical loading stress imposed during periods of high intensity, high volume
exercise, athletes may be subject to periods of metabolic stress due to inadequate energy
consumption either as a means of improving body composition or attaining a bodyweight
requirement for competition. Often times a consequence of inadequate energy intake during
these periods is a reduction in muscle mass and/or function due to insufficient recovery and
decreased nutrient ingestion (Ratamess et al. 2003 & Kramer et al. 2006). A means of preventing
muscle catabolism and decreased muscular performance that permits the desired losses in body
mass and/or body fat would be advantageous for athletes during periods of weight loss and
inadequate nutrient intake. To examine the effects of varying protein and amino acid intake
during caloric restriction (28kcal/kg per day) on body composition and performance, Mourier,
Bigard, de Kerviler, Roger, Legrand, & Guezzenec (1997) conducted a 19-day study involving
25 competitive wrestlers randomly assigned to one of one of three hypocaloric diets with varying
levels of protein and BCAA or a fourth group that consumed a control diet. Post-trial
measurements revealed that the group consuming the hypo-caloric, high-BCAA diet providing
24.4kcal/kg bodyweight with 20% protein (including .9g/kg bodyweight per day of BCAA), 60%
carbohydrate, and 20% fat, achieved the greatest reductions in bodyweight (4kg, p < 0.05) and
body fat percentage (17.3%, p < 0.05), with a significant decrease in abdominal visceral adipose
tissue (-34.4%, p < 0.05). Although Mourier et al. (1997) found no change in aerobic (VO2 max)
(p > 0.75) or anaerobic capacities (Wingate test) (p > 0.81), nor in muscular strength (p > 0.82),
they report that daily consumption of .9g/kg bodyweight during 19 days of caloric restriction and
weight loss preserved muscle mass, decreased fat tissue, and maintained performance in
wrestlers.
Effects of EAA and BCAA on Muscular Adaptation and Performance
As discussed previously, there are beneficial effects of EAA and BCAA ingestion on cellular
signaling, muscle protein synthesis, reductions in muscle damage, maintenance of and
accelerated improvements in qualities of muscular strength during periods of high physical and
metabolic stress, and preservation of lean muscle tissue during weight loss (Ratamess et al. 2003,
Kraemer et al. 2006, Tipton et al. 2009, Pasiakos et al. 2011, Mourier et al. 1997, Hoffman et al.
2009, & Cribb & Hayes 2006). A further question for the efficacy of EAA and BCAA ingestion
is whether these practices can produce improvements in performances during resistance training
programs not utilizing overreaching, endurance, and interval training.
In a study conducted by Ispoglou et al. (2011) 26 initially untrained men were divided into
groups consuming supplements of either 4 grams per day (~50 mg/kg bodyweight) of leucine or
an isocaloric amount of lactose on a daily basis for 12 weeks. The participants maintained their
habitual diet throughout the experimental period. On non-training days participants were asked
to take the supplements in three equal doses during the day (morning, midday, evening). On
training days, the supplements were ingested immediately following exercise. Subjects
participated in a twice-per week resistance training program consisting of eight exercises. 5RM
strength and body composition were assessed at the start and conclusion of the 12 week program.
Subjects in the leucine group achieved significantly higher gains in total 5RM strength (sum of
5-RM in eight exercises) and 5-RM strength in five out of the eight exercises (p < 0.05). The
percentage total 5RM strength gains were 40.8% (± 7.8) and 31.0% (± 4.6) for the leucine and
placebo groups respectively. With an average of ~10% greater improvement in 5RM over the
placebo group, the leucine group displayed significantly greater mean gains in the leg press (p =
0.010), bench press (p = 0.02), pullover (p = 0.03), preacher curls (p = 0.004), triceps press (p =
0.002) and total strength (p < 0.001). There were no significant differences in improvement
between conditions for leg curls (p = 0.19), chest cross (p = 0.08) and overhead press (p = 0.35).
In further support of increased muscular strength following EAA/BCAA ingestion, Viellevoye et
al. (2010) reported that during a 12-week strength training program, subjects consuming two
daily servings of a supplement of 15 grams EAA containing 6.1grams BCAA) increased their
strength by 16.7 ± 8.5% (p < 0.001) in the bench press, while the subjects of the placebo group
improved 12.6 ± 11.4% (p < 0.001). In the squat exercise, the EAA group showed a significant
increase of 5.8 ± 8.7% (p < 0.001) with no significant difference achieved for the placebo group
(4.8 ± 9.6%). Together, these improvements in strength with EAA and BCAA ingestion along
with the preservation of and tendency towards improved muscular performance during
overreaching training programs supports the use of EAA and BCAA supplementation as a means
of enhancing the adaptive response to resistance training and producing improvements in
measures of strength.
Improvements in performance following continuous, endurance-type exercise have also been
reported with amino acid consumption. Thomson, Ali, and Rowlands (2011) evaluated the
effects of ingestion of either leucine-protein, high-carbohydrate nutrition (0.1/0.4/1.2/0.2 g·kg–
1·h–1; leucine, protein, carbohydrate, fat, respectively) or isocaloric control (0.06/1.6/0.2 g·kg–
1·h–1; protein, carbohydrate, fat, respectively) nutrition for 1.5 h post-exercise in 10 well trained
male cyclists and triathletes. Subjects performed interval training sessions in the evening on each
of three consecutive days. The sessions were characterized as “very hard”, “moderate”, and
“hard”, with durations of 120-150minutes each. Subjects consumed either the supplement or
control beverages during the first 90 minutes after the exercise bouts. Diet was controlled over
the course of the three day trial and protein was provided at 1.6 g·kg–1·day–1. On the morning
following each exercise session, participants from each group consumed the alternate beverage
to ensure total nutrient intake throughout each day was normalized between trials and the effect
of treatment could be isolated to the post-exercise period. A repeat-sprint test was performed
prior to the study and again after 39 hours of recovery following the third exercise bout. Post-
exercise leucine + protein ingestion improved mean sprint power by 2.5% (p = 0.013) over the
control conditions (325 and 320 watts respectively). Because the only variable in nutrient intake
between groups was the provision of leucine following exercise as opposed to the following
morning, it can be suggested that recovery of performance in repeated-sprints is greater when the
BCAA leucine is provided following the completion of exercise. Crowe, Weatherson, and
Bowden (2006) provided 13 competitive outrigger canoeists (VO2 max 47.1 ± 2.0ml·kg-1·min-1)
with .45mg/kg bodyweight of leucine or corn flour placebo daily for six weeks. The leucine
group had greater improvements in 10 second rowing power (6.7 ± 0.7 watts·kg-1 vs. 6.0 ± 0.7
watts·kg-1) than the placebo group and increased their rowing time to exhaustion at a workload of
70-75% VO2 max (from 77.6 ± 6.3 minutes to 88.3 ± 7.3minutes) while the placebo group had no
change in rowing time to exhaustion (Crowe et al. 2006).
Safety of Amino Acid Consumption
Ispoglou et al. (2011) found no evidence to suggest that ingestion of 4 grams per day of leucine
during a 12-week period of resistance training negatively affected the health of the male
participants as indicated by tests of liver function and full blood counts. In their review Campbell
et al. (2007) reported that protein intakes exceeding the RDA do not pose health risks for
healthy, exercising individuals. Furthermore, Gleeson (2005) identified that while excessive
protein intakes equal to or greater than 3g/kg per day may have side effects including kidney
damage, increased blood lipoprotein levels, and dehydration due to urinary nitrogen excretion,
protein intakes as high as 1.8g/kg bodyweight do not seem to be harmful and acute intakes of 10-
30grams per day of BCAA do not appear to have negative effects on health.
Limitations and Discussion
While there is a consistency of results in many of the studies reviewed, limitations of these
investigations included impact of differing resistance training protocols and the total volume,
intensity, and musculature involved. The amount of amino acids required to produce maximal
protein synthesis following exercise may be related to the contraction-induced stimulation
resulting from the muscle mass involved, the volume of work performed, and intensity of work
performed (Tipton et al. 1999 & Kraemer et al. 2006). Variations in each of these elements may
influence contraction-induced muscular damage, extent of signaling for protein synthesis,
substrate requirement for synthesis, and stimulus to increase muscular performance. However,
despite the variation in total work as well as mode of exercise (resistance, cycling, running, and
eccentric exercise) there is consistency in the findings that provision of EAA and BCAA prior to
and during the exercise bout improves protein synthesis, reduces muscular breakdown, and
enhances recovery and adaptation to exercise over placebo, carbohydrate, and complete protein
(Pasiakos et al. 2011, Tipton et al. 1999, Tipton et al. 2001, Kraemer et al. 2006, & Sugita et al.
2003).
One confounding variable of the work examining the effects of amino acid intake is the variation
in dietary habits of subjects. Though some investigators controlled the nutrient consumption of
their subjects, the variation between studies still exists. Because the BCAA cannot be
synthesized in the body food sources of complete protein, protein supplements, or amino acid
mixtures must be consumed in order to obtain the EAA including the BCAA (Mero 1999). The
source and rate of appearance of amino acids in the blood has been identified as a determining
factor in the rate of protein synthesis making supplemental proteins and specific amino acid
arrays more effective than whole food proteins (West et al. 2011). In regard to protein synthesis
and recovery, it is possible that even with sufficient provision of amino acids during and around
the exercise period, insufficient ingestion of addition amino acids or complete protein throughout
the remainder of the day could prevent the realization of maximum adaptation to exercise
(Campbell et al. 2007). Similarly, dietary supply of an excess of protein and amino acids could
potentially mask the effects of amino acids, particularly if the ingestion of dietary protein and
subsequent circulation of amino acids overlapped with the exercise or supplementation protocols
used in the research. However, Vieillevoye et al. (2010) observed that the addition of 15g EAA
(6.1g BCAA) to breakfast and dinner for 12 weeks in subjects whose diets already provided
sufficient protein to achieve nitrogen balance resulted in greater post-meal protein synthesis over
placebo that lead to increased muscle mass(1.1kg vs. 0.8kg). This finding of Vieillevoye et al.
(2010) supports the use of BCAA and EAA to stimulate protein synthesis even under conditions
of adequate protein intake.
Time of ingestion influences the effect of amino acids on protein breakdown and protein
synthesis. The critical time period for consumption of EAA/BCAA appears to be during the 30
minutes immediately preceding, throughout, and at the conclusion of exercise (Nosaka et al.
2006 & Tipton et al. 2001). Delaying the provision of amino acids until after exercise reduces the
delivery and uptake to the working musculature and reduces the mTOR signaling and protein
synthetic response (Tipton et al. 2001). Furthermore, the provision of EAA/BCAA prior to
exercise has been shown to suppress protein breakdown during the exercise bout (Pasiakos et al.
2011 & Tipton et al. 2001). When consumed as powders or pills along with liquids, amino acids
appear in the blood and are available for uptake approximately 15-30 minutes after ingestion
(Nosaka et al. 2006 & Shimomura et al. 2006). Timing the intake of amino acids to coincide with
the start of exercise to make them available for use during the period when exercise-induced
mTOR activation is at its greatest may be the best approach to minimizing protein breakdown
and maximizing protein synthesis (Drummond et al. 2009, Ge et al. 2009, Tipton et al. 2001, &
Pasiakos et al. 2011).
Another limitation of the available research is the variation in the dosage and mixture of amino
acids. While some studies provided relatively conservative amounts of 3-10g mixed amino acids
(EAA and NEAA), other studies employed supraphysiological amounts of EAA or BCAA up to
.9g/kg bodyweight daily (Cuthbertson et al. 2005, Glynn et al. 2010, & Mourier et al. 1997).
Because the BCAA have been identified to enhance signaling, but do not completely satisfy the
requirement for all EAA in regard to protein synthesis, it is difficult to discern the specific
independent effects of the EAA and BCAA when they were not supplied as separate protocols.
Nevertheless, the identification that increasing amounts of EAA up to approximately 10g
produces maximal stimulation in the absence of exercise by Cuthbertson et al. (2005) and Glynn
et al. (2010) provides support that 10g EAA is the minimum dosage to be consumed prior to or
during exercise to maximize effectiveness. In support of an advantage to dosages above 10g,
Tipton et al. (1999) observed greater protein synthesis with a 34.5g dose of EAA (16.6g BCAA)
compared to a 17.96g dose of EAA (8.9g BCAA) provided following resistance exercise.
Therefore, it can be suggested that a minimum of 17.96g EAA with at least 8.9g BCAA should
be consumed during the critical time period prior to and during the exercise bout, with greater
protein synthesis likely resulting from greater intakes (Tipton et al. 1999 & Nosaka et al. 2006).
It has been identified that the EAA, and most efficiently the BCAA, activate the mTOR signaling
cascade that regulates the initiation of protein synthesis (Atherton et al. 2010, Karlsson et al.
2004). Furthermore, the BCAA and EAA are required substrates for the synthetic process. While
the BCAA and EAA are both stimulators of mTOR signaling, the BCAA, primarily leucine, are
more efficient than the EAA in activating mTOR (Pasiakos et al. 2011 & Balage & Dardevet
2010). Both the BCAA and EAA serve as substrates for protein synthesis, however the role of
the EAA becomes more significant as mTOR signaling increases and protein synthesis persists
due to their availability being a rate-limiting step in the synthetic process (Kraemer et al. 2009 &
Bohé et al. 2003). Therefore, because protein synthesis is activated to a greater extent by the
presence of the BCAA and the synthetic process continues only with sufficient EAA, the most
effective supplementation protocols for maximizing protein synthesis and minimizing protein
breakdown will include adequate amounts of the EAA with a high proportion of BCAA
(Kraemer et al. 2009, Pasiakos et al. 2011, & Balage & Dardevet 2010).
Conclusion:
The recommendation for achieving maximized net protein balance, recovery, and performance
improvement is to between 10g and 34.5g of EAA with a high proportion (50% or greater) of
BCAA beginning 15-30 minutes prior to the start of exercise and throughout the exercise bout
(Tipton et al. 1999, Karlsson et al. 2004, & Pasiakos et al. 2011). This timing of ingestion will
lead to a rise in blood amino acid levels and intracellular signaling during the exercise period
when muscular contraction will provoke further anabolic signaling and the elevated blood flow
to recruited muscles will maximize the delivery of the ingested amino acids to serve as substrate
for protein synthesis (Nosaka et al. 2006 & Shimomura et al. 2006). Given the greater delivery
and uptake of amino acids in the exercising muscle ingestion of the BCAA and/or EAA prior to
exercise should also prevent muscle breakdown and in concert with the elevated protein
synthesis will provide the maximum net protein balance (Pasiakos et al. 2011 & Tipton 2001).
The ability to maintain performance and speed recovery during high-stress phases of training not
only permits the athlete to incorporate these periods of training on a more frequent basis, it is
possible that the sum of the adaptive response over time and thus the improvement in
performance will be greater due to earlier recovery and exposure to greater training loads
(Ratamess et al. 2003 & Kraemer et al. 2006). Amino acid ingestion is not only beneficial in the
long-term adaptation to high-intensity exercise, but also in preservation of performance under
acute periods of stress. During the competitive season the application of amino acid
supplementation could maintain or potentially improve performance when the athlete is
competing at maximum intensity. The efficacy, availability, safety, and ease of application of
EAA and BCAA supplementation to enhance net protein balance, muscular recovery, and
adaptation to exercise makes them an ideal supplement for all populations in pursuit of
performance outcomes.
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