The studies are mixed regarding BCAA supplementation and muscle protein synthesis (MPS) with some indicating that they do stimulate MPS and others showing no effect on MPS but a decrease in protein breakdown (Louard 1990).
In a study examining BCAA supplementation during caloric restriction in elite wrestlers, 25 subjects were given a hypocaloric control diet, hypocaloric high protein diet, hypocaloric low-protein diet or hypocaloric high BCAA diet for 19 days. The BCAA group lost a significant amount of bodyweight (-4 kg, p < 0.05) and body fat (-17.3%, p < 0.05) in comparison to other groups. In addition the BCAA group experienced a significant reduction in abdominal visceral adipose tissue. There were no between group differences in anaerobic capacity, VO2max, or muscular strength (Mourier 1997).
BCAAs and Endurance
The research to date examining BCAAs and endurance exercise has looked into central fatigue, BCAAs and the immune response and BCAAs and fatigue as well as performance.
Some studies indicate that BCAAs may impact fatigue during prolonged exercise whereas others indicate that BCAAs have no effect on fatigue (Hargreaves 2001) or performance.
Though there is considerable BCAA oxidation during endurance exercise, supplementation in an effort to up-regulate protein synthesis is most likely futile. Protein metabolism becomes more efficient and, if energy requirements are met, BCAA oxidation is limited thereby making supplementation unnecessary (Shimomura 2004, Gibala 2007). Studies on BCAA supplementation in endurance athletes bring mixed results.
In a randomized, double-blind study in 10 endurance-trained males, subjects were given either placebo (6% sucrose solution), tryptophan (6% sucrose + 3 g tryptophan), low-dose BCAA (6% sucrose solution with 6 g BCAA) or high-dose BCAA (6% sucrose with 18 g BCAA) during a maximal power cycle ergometer test. Exercise time until exhaustion was not different between groups (van Hall 1995). In a double-blind, placebo-controlled study, sixteen subjects participated in a 21-day trek at high altitudes were supplemented with either placebo or 11.5 g BCAA. Both groups lost fat mass (11.7% and 10.3% in BCAA and placebo respectively) though the BCAA group gained a slight amount of lean body mass (1.5%). Lower limb maximal power decreased less in the BCAA vs. placebo
(2.4% vs. 7.8%). In addition, the placebo group experienced a 6.8% decrease in arm muscle cross sectional area vs. no change in BCAA. These results suggest that BCAAs have an anticatabolic effect and help protect against losses of muscular power as a result of exhaustive exercise at high altitudes (Schena 1992). In a study examining the affects of BCAA on intermittent high-intensity running to fatigue, 8 subjects were given either a carbohydrate beverage with or without BCAAs. Subjects performed 3 exercise trials consisting of intermittent shuttle running (walking, sprinting, and running) to fatigue. Subjects drank either carbohydrate drinks given 1 h before (5 mL/kg, 18% carbohydrate) and during exercise (2 mL/kg, 6% carbohydrate) (CHO), carbohydrate drinks with BCAA (7 g) added to the portions consumed 1 h before and immediately before exercise (CHO+BCAA), or flavored water placebos (P). Subjects ran longer when fed either CHO or CHO+BCAA as compared to P, with no differences between CHO and CHO+BCAA. This study indicates that BCAA may provide no further benefit than carbohydrate alone on intermittent high-intensity exercise to fatigue (Davis 1999).
Research shows that BCAA supplementation has an anti-catabolic effect in the recovery period after exercise (Blomstrand 2000) and can potentially attenuate the muscle damage and soreness associated with intense exercise. In addition to muscle damage, leucine plays a role in the regulation of MPS (Norton 2006). In this regard, one of these studies used an endurance bout of exercise (2 h cycling ride at about 70% of max VO) while supplementing with either a placebo or 12 2
grams/day BCAAs. The researchers discovered that when supplementing with the BCAAs, peak levels of enzymes reflective of muscle damage (e.g., LDH and CK) were delayed from 2 hrs to 5 days for LDH and from 4 hrs to 5 days post-test for CK, which led them to conclude that BCAA supplementation may help reduce muscle damage associated with endurance exercise (Coombes 2000).
A recent double-blind, crossover study examined BCAA supplementation and tissue damage during distance running. Eight male distance runners (aged 20.4 ? 1.2 yrs) participated in 25-km runs where they were given either a drink containing BCAA (0.4% BCAA in a 4% carbohydrate solution) or an isocaloric placebo drink 5 times during the run without any restriction in the volume ingested. Blood BCAA and lactate dehydrogenase (LDH) level, were measured pre- and post-run. The total volume of the drink consumed did not differ significantly between trials 591+/-188 (2.36 g BCAA) vs 516+/-169 mL in BCAA and placebo trial, respectively. LDH, a marker of muscle damage, increased in both trials but this increase was significantly less in the BCAA trial (48% vs 58%, P<0.05) indicating that BCAAs may help attenuate muscle damage during long distance runs. (Koba 2007)
BCAA supplementation has also been associated with recovery from resistance training. In a randomized, placebo-controlled crossover study, male and female subjects (n=30; 21-24 yrs old) were supplemented with a BCAA solution (92 ? 2 mg/kg in the females and 77 ? 3 mg/kg in the males) 15 minutes prior to a squat exercise test (7 sets of 20 squats with 3 minute intervals between sets) used to induce muscular fatigue and delayed onset muscle soreness. DOMS was assessed by using a visual –analogue scale. DOMS on days 2-5 post exercise was
significantly lower in females in the BCAA trial vs. the placebo trial. In male subjects, DOMS tended to be lower throughout the 5 days after the test though results were not reach statistical significance. Muscular fatigue tended to be lower in all BCAA trials vs. placebo on days 2-5. These results indicate that approximately 5g BCAA/day in a 120 lb female can reduce DOMS and muscle fatigue for several days post-exercise (Shimomura 2006). Another study using 77mg/kg BCAA supplementation showed suppression of endogenous muscle protein breakdown during resistance exercise (single leg knee extensions performed for 60 minutes at 71% maximal work capacity) (MacLean 1994).
Two studies used eccentric muscle contractions to invoke much higher levels of muscle damage while supplementing with HMB, a derivative of the amino acid leucine. The first study supplemented subjects with 3 grams of HMB for 14 days prior to the damage bout and found that: 1) soreness was reduced after 24 hours; 2) CK levels were decreased after 24 hours; and 3) force production and swelling were decreased, all of which are characteristics of muscle damage (Van Somere 2005). Another study used a similar protocol and suggested a supplementation period of at least 14 days with BCAA or HMB is needed to impart positive alterations in the muscle damage response (Paddon-Jones 2001). Findings from these studies are very important for those interested in muscle recovery and suggest that increasing the circulating levels of amino acids, specifically leucine and the BCAAs may be effective at minimizing the symptoms associated with muscle damage (Van Somere 2005, Paddon-Jones 2001).
Timing of EAA and Protein
Though it is clear that EAAs are necessary for stimulating MPS, the exact dosage per kg bodyweight, for maximal MPS remains unknown. EAA studies indicate that
there is a dose-response relationship to EAA consumption and MPS though as little as 6 grams of EAAs will effectively stimulate MPS (Borsheim 2002). Non-essential amino
acids do not affect MPS (Tipton 1999, Borsheim 2002).
Previous research in this area emphasizes the importance of taking EAAs with a simple carbohydrate (sucrose) about 30 minutes prior to resistance training and that this may be more important for stimulating MPS than taking EAAs post-
exercise (Tipton 2001). Though this study indicates the timing of EAAs may be very important in stimulating MPS, a recent study indicates that the timing of intact protein ingestion is not as important. Seventeen healthy subjects were given 20 grams of whey protein (this corresponds to approximately 9 grams EAA) pre or post exercise (10 sets of 8 repetitions of the leg extension). Amino acid uptake was not significantly different pre vs. post (Tipton 2006). In addition, when comparing this study to the results of the previously mentioned study (both by the same group of researchers), the increase in arterial amino acid concentrations during exercise was approximately 100% for EAA (Tipton 2001) but only approximately 30% for whey proteins when ingested prior to exercise. This comparison indicates that amino acid delivery during exercise is greater when EAA is ingested than intact whey protein prior to exercise (Tipton 2006).
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