AMINO ACIDS: ERGOGENIC THEORY
Amino acids are theorized to enhance performance in
a variety of ways, such as increasing the secretion of
anabolic hormones, modifying fuel use during
exercise, preventing adverse effects of overtraining,
and preventing mental fatigue. The following
discussion highlights research regarding the
ergogenic effects of individual amino acids, various
combinations of amino acids, and several special
protein dietary supplements.
Tryptophan. Tryptophan (TRYP), is a precursor for
serotonin, a brain neurotransmitter theorized to
suppress pain. Free tryptophan (fTRYP) enters the
brain cells to form serotonin. Thus, tryptophan
supplementation has been used to increase serotonin
production in attempts to increase tolerance to pain
during intense exercise. One study reported
significant improvements in time to exhaustion at 80 percent of maximal oxygen uptake, accompanied by
significant reductions in the rating of perceived
exertion 8
. However, research with a more
appropriate experimental design did not replicate
these findings 9
. Moreover, other investigators
reported no effect of TRYP supplementation on
aerobic endurance performance at 70-75 percent of
maximal oxygen uptake 6
. Tryptophan does not
appear to be an effective ergogenic 10.
Branched chain amino acids (BCAA). Some
investigators believe that increased levels of
serotonin may cause fatigue 11. During prolonged
aerobic endurance exercise, muscle glycogen may
become depleted and the muscle may increase its
reliance on BCAA for fuel, decreasing the plasma
BCAA:fTRYP ratio. Because BCAA compete with
fTRYP for entry into the brain, a low BCAA:fTRYP
ratio would facilitate the entry of fTRYP to the brain
and the formation of serotonin. Hypothetically,
BCAA supplementation may delay central nervous
system fatigue and enhance performance in
prolonged aerobic endurance events by increasing the
BCAA:fTRYP ratio and mitigating the formation of
serotonin.
BCAA supplementation has been studied for its
effects on various types of exercise performance,
including ratings of perceived exertion (RPE) during
exercise and mental performance following exercise.
In general, the findings are equivocal, as are the
conclusions from several recent reviews. One
investigator concluded that BCAA supplementation
reduces RPE and mental fatigue during prolonged
exercise and improves cognitive performance after
exercise, and also suggests that in some situations
BCAA supplementation may improve physical
performance, such as during exercise in the heat or in
actual competitive races where central fatigue may be
more pronounced than in laboratory experiments 12.
However, other reviewers conclude that most studies
show no effects of BCAA supplementation on
performance, such as prevention of fatigue during
prolonged exercise 13,14 two recent studies support
these conclusions. Watson and others 15 reported no
beneficial effects of BCAA supplementation,
consumed before and during prolonged cycling to
exhaustion at 50 percent V02max in the heat, on
performance time, heart rate, and core or skin
temperature. Cheuvront and others 16 reported similar
findings with subjects exercising in the heat, noting
no significant effect of BCAA supplementation on
time-trial performance, cognitive performance, mood,
perceived exertion, or perceived thermal comfort.
Although current research does not support an
ergogenic effect of BCAA supplementation, most
investigators recommend additional research.
Glutamine. Glutamine may be theorized to be
ergogenic in various ways 6
. It is an important fuel
for some cells of the immune system, such as
lymphocytes and macrophages, which may be
decreased with prolonged intense exercise, such as
that related to overtraining. Glutamine may also
promote muscle glycogen synthesis, and has been
studied for potential enhancement of muscular
strength.
Several investigators theorize that athletes who
overtrain may experience decreased plasma
glutamine levels, which may impair functions of the
immune system and predispose the athlete to various
illnesses 17,18. Illness may impair training and
eventual performance. Research findings are
equivocal, with some studies reporting lower
incidence rates of infection among athletes who
consumed a glutamine-supplement drink following
intense training 19. However, others reported that
although glutamine supplementation helped maintain
plasma glutamine levels following intense exercise, it
had no effect on various tests of the immune response
20. Recent reviews indicated that there is little support
from controlled studies to recommend glutamine
ingestion for enhanced immune function 14,21.
Although glutamine may simulate muscle glycogen
synthesis, reviewers recently concluded that there is
no advantage over ingestion of adequate
carbohydrate alone 14. Moreover, several recent
studies indicate that neither short-term nor long-term
glutamine supplementation has an ergogenic effect
on muscle mass or strength performance. Glutamine
supplementation one hour prior to testing had no
effect on resistance exercise to fatigue, nor did six
weeks of glutamine supplementation during
resistance training increase lean muscle mass or
strength more so than the placebo treatment 22,23.
Aspartates. Potassium and magnesium aspartates are
salts of aspartic acid, an amino acid. They have been
used as ergogenics, possibly by enhancing fatty acid
metabolism and sparing muscle glycogen utilization
or by mitigating the accumulation of ammonia during
exercise. The effect of aspartate supplementation on
physical performance is equivocal, but about 50
percent of the available studies have indicated
enhanced performance in exercise tests of aerobic
endurance 6
. Additional research is needed to study
the potential ergogenicity and underlying
mechanisms of aspartate salt supplementation.. Arginine. Arginine supplementation may be
theorized to be ergogenic because it is a substrate for
nitric oxide (NO) synthesis, a potent endogenous
vasodilator that may benefit blood flow and
endurance capacity. Several studies involving
patients with peripheral arterial disease or clinical
symptoms of stable angina pectoris have shown
improved exercise capacity with arginine
supplementation 24,25. However, research involving
the independent effect of arginine supplementation
on the aerobic endurance capacity of healthy athletes
has not been uncovered 6
.
Ornithine, lysine and arginine. Ornithine, lysine and
arginine have been used in attempts to increase
human growth hormone (HGH) production, the
theory being to increase lean muscle mass and
strength. However, although limited data are
available, a number of well-controlled studies,
several with experienced weight lifters, reported no
increases in HGH levels or various measures of
muscular strength or power 26-28.
Chromiak and Antonio 29 reviewed the scientific
studies on growth-hormone releasing amino acids
(ornithine, lysine and arginine) and indicated that oral
doses that are great enough to induce significant
growth hormone release are likely to cause
gastrointestinal discomfort. Moreover, they reported
that no studies found that pre-exercise oral amino
acid supplementation augments growth hormone
release. They also concluded that no appropriately
conducted scientific studies found that oral
supplementation with such amino acids before
strength training increases muscle mass and strength
to a greater extent than strength training alone. They
do not recommend the use of specific amino acids to
stimulate growth hormone release.
Tyrosine. Tyrosine is a precursor for the
catecholamine hormones and neurotransmitters,
specifically epinephrine, norepinephrine, and
dopamine. Some have suggested that inadequate
production of these hormones or transmitters could
compromise optimal physical performance. Thus, as
a precursor for the formation of these hormones and
neurotransmitters, tyrosine has been suggested to be
ergogenic. However, in a well-designed placebocontrolled,
crossover study, Sutton 30 and others
found that tyrosine supplementation (150
milligrams/kilogram body weight) consumed 30
minutes prior to taking a series of physical
performance tests significantly increased plasma
tyrosine levels, but had no significant ergogenic
effects on aerobic endurance, anaerobic power, or
muscle strength.
Taurine. Taurine is a non-essential sulfur-containing
amino acid, but it lacks a genetic codon to be
incorporated into proteins or enzymes. Nevertheless,
it plays a role in several metabolic processes, such as
heart contraction and antioxidant activity. Taurine is
an ingredient in several so-called energy drinks, such
as Red Bull.
Baum and Weiss 31 reported that Red Bull, which
contains taurine and caffeine, as compared to a
similar drink without taurine, favorably influence
cardiac parameters, mainly an increased stroke
volume, during recovery after exercise; however,
physical performance was not tested. However,
Zhang and others 32 reported that 7 days of taurine
supplementation induced significant increases in
V02max and cycle ergometer exercise time to
exhaustion; the ergogenic effects were attributed to
taurine’s antioxidant activity and protection of
cellular properties.
Amino Acid Cocktails. Providing an ample supply of
essential amino acids to the muscle within 1-3 hours
before or following exercise may help to further
muscle protein synthesis. Gibala 33 indicated that
consumption of a drink containing about 0.1 gram of
essential amino acids per kilogram of body weight (7
grams for a 70-kilogram athlete) during the first few
hours of recovery from heavy resistance exercise will
produce a transient, net positive increase in muscle
protein balance. Gibala also noted that it is uncertain
if ingesting amino acids, either alone or combined
with carbohydrate, immediately before exercise or
during recovery further enhances the rate of muscle
protein buildup during recovery. Some investigators
have suggested that it may