Transcript 投影片 1

Effect of Branched Chain Amino
Acids (BCAA) on Prolonged
Physical Activity
BCAA
Branched chain amino acids (leucine, isoleucine, and
valine), or BCAA's, are a group of essential amino
acids that play important roles in protein synthesis
and energy production.
In humans, about 15-25% of total protein intake is
BCAA's, and dairy products are particularly high in
them
BCAA's make up 35-40% of the essential amino
acids in body protein and 14% of the total amino
acids in skeletal muscle
One of the most important BCAA's is leucine, and
estimates of dietary requirements for leucine range
from 1-12 g daily
Amino acid
The use of supplemental BCAA's has been
researched for a variety of purposes
– in the treatment of liver failure
– catabolic disease states
– improve exercise performance
BCAA and Exercise
a significant decrease in plasma leucine levels
after aerobic, anaerobic, and strength
exercise .This is due to increased BCAA
metabolism in muscle tissue.
Supplementation with leucine or BCAA's in
both the short and long term prevents the
exercise-induced decline in plasma BCAA's
and increases muscle BCAA concentration
BCAA's may spare muscle and liver glycogen
stores and increase fuel supply
Muscle content of glycogen in biopsy samples taken at rest,
during exercise, and in the recovery after exercise in the normal
(A)- and low (B)-glycogen legs in the 2 conditions. ○,
Branched-chain amino acid (BCAA) condition; ●, placebo
condition. Values are means ± SE for 7 subjects
The BCAA's are the only amino acids that are
not readily degraded in the liver
Leucine & protein synthesis
In skeletal muscle, leucine stimulates protein
synthesis through multiple independent
mechanisms. The first mechanism is
increased insulin secretion
leucine stimulates protein synthesis through
the mammalian target of rapamycin (mTOR)*
pathways, 70-kDa ribosomal protein S6 kinase
activity.
* mTOR is a serine/threonine protein kinase that regulates cell growth, cell
proliferation, cell motility, cell survival, protein synthesis, and transcription.
70-kDa S6 protein kinase (p70S6k) phosphorylation
at Ser424/Thr421 in skeletal muscle at rest and after
exercise during placebo and BCAA trials.
Representative immunoblots are shown (top).
Values in graph are arbitrary units (means ± SE for
7 subjects). #P < 0.05 vs. rest; *P < 0.05 for BCAA
vs. placebo
leucine also enhances eIf4E-binding protein
phosphorylation and the association of
eukaryotic initiation factor (eIF)4E* with
eIF4G, effects that have been determined both
in vitro and in vivo in humans
*proteins involved in the initiation phase of eukaryotic translation. eIF4E
recognizes and binds to the 5' cap structure of mRNA, while eIF4G binds
to Poly(A)-binding protein which binds the poly(A) tail, circularizing and
activating the bound mRNA
An additional mechanism for improved
exercise performance from BCAA's is
inhibition of CNS fatigue.
BCAA's share the same transporter system
with tryptophan (the serotonin precursor
amino acid), so BCAA supplementation causes
competitive inhibition of tryptophan transport
to the brain, and this in turn reduces serotonin
levels.
Exercise increases the tryptophan/BCAA
ratio in the bloodstream, and a BCAA
supplement may prevent or reverse this.
Further, animal studies find that tryptophan
administration reduces exercise performance
This means that in theory, BCAA's could
increase exercise performance by decreasing
buildup of serotonin in the brain. Multiple
studies indicate that BCAA supplements
successfully change the tryptophan/BCAA
plasma ratio, especially during more prolonged
exercise
Muscle concentration of tyrosine (A and B) and
phenylalanine (C and D) in biopsy samples taken at rest, after
exercise, and in recovery after exercise in the normal (A and
C)- and low (B and D)-glycogen legs in the 2 conditions. ,
BCAA condition; , placebo condition. Values are
means ± SE for 7 subjects. *P < 0.05 for BCAA vs. placebo.
F-tryp/BCAA and Central Fatigue
Low levels of BCAA in conjunction with high
levels of free-tryptophan (F-tryp) in the blood
could cause central fatigue
F-tryp is needed for the formation of the brain
neurotransmitter serotonin, which may depress
the central nervous system and induce
symptoms of sleepiness and fatigue.
The amount of F-tryp
entering the brain to form
serotonin is limited for two
reasons:
– High level of BCAA block the
entry of F-tryp in the brain
– tryptophan is normally bound
with the blood protein
albumin, so it is not free
F-tryp may gain easier entry to the brain for
tow reasons:
– as muscle glycogen levels fall, the BCAA
levels in the blood might also fall because
they may be used to compensate for the
decreased energy production from glycogen
– free fatty acid (FFA), which are bound to
albumin for transport in the blood, increase
and therefore decrease the amount of
albumin available to bind with tyrpophan.
Results of the recent Danish study
suggest that an intake of BCAA has an
anabolic effect on protein metabolism
during the recovery period after exercise rather
than during the actual exercise
Ingestion of BCAA repeatedly during exercise
and recovery in an amount of 100 mg/kg body
weight does not increase the rate of release
of ammonia from the muscle
Ingestion of BCAA caused the concentration of these
amino acids to increase by 135% in the plasma and
by 57% in muscle tissue during exercise.
The plasma concentration of alanine increased by
48% during exercise when BCAA were ingested, and
the increase in the muscle concentration of alanine
during exercise was larger (70% versus 31% in the
placebo trial), suggesting an increased rate of alanine
production.
Arterial concentration and rate of exchange of glucose and lactate during exercise and
recovery. Open symbols, BCAA condition; filled symbols, placebo condition. Values for
arterial concentrations are means ± SE of 7 subjects and for rates of exchange are means ± SE
of 6 subjects. *P < 0.05 for BCAA vs. placebo.
Arterial concentration and rate of exchange of ammonia and free fatty acids (FFA) during
exercise and recovery. Open symbols, BCAA condition; filled symbols, placebo condition.
Values for arterial concentrations are means ± SE of 7 subjects; values for rates of exchange
are means ± SE of 6 subjects.
Arterial concentrations of insulin, growth hormone, and norepinephrine during exercise and
recovery in the 2 conditions. □, BCAA condition; ■, placebo condition. Values are
means ± SE of 7 subjects.
Typical claims for BCAA-based
products
Increased endurance 增加耐力
Prevention of fatigue 預防疲勞
Improved mental performance增進身心健康、增強
意志力
Increased energy levels 增強能量
Improved immune system function 加強免疫系統
Improved post-exercise recovery (less muscle
soreness and fewer upper respiratory tract infections)
促使運動後恢復
Discussion
Due to its high F-tryp content, before training
or competition what kind of FOOD should
avoid to massive intake and why.
In your opinion what kind of sport event
requires BCAA supplement for its athlete and
why.
Why serotonin can cause central fatigue and
then decrease work capacity