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
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