|Image 1: Without the other essential amino acids (EAAs), the branched chain amino acids, leucine, isoleucine and valine (BCAAs) have nothing to "build" your muscle from ;-)|
BCCAs work! How? Little do we know...
If we are honest, we must concede that our (=the scientific) understanding of the complex processes that are triggered when "large" amounts of BCAAs hit our bloodstream, is very limited. What we know is that we can measure increases in mTOR-expression that correlate with likewise measurable increases in protein synthesis. What we do not really know is how exactly one leads to the other and where the influences of amino acid supplementation and exercise training overlap. This is even more true for the complementary side of the protein synthetic equation of which Borgenvik et al. state that
[w]hereas extensive evidence for the stimulatory effect of amino acids, either alone or in combination with exercise, on protein synthesis has been reported, their effect on protein breakdown is elusive.In that, it is particularly confusing that "previous investigations involving ingestion of essential amino acids (EAA) in connection with resistance exercise have revealed no attenuating effect on protein breakdown", while studies which investigated the effect of BCAA or leucine in isolation, report reduction in protein degradation in subjects at rest or performing eccentric endurance exercise (MacLean. 1994). Reason enough for the Swedish scientists to recruit a group of seven healthy, recreationally active participants (5 men, 2 women; 27 (± 2) years; height 175 (± 5) cm; weight 67 (± 7) kg), put them on a standardized diet (17% protein; 25% fat; 57% carbs; ~2100kcal for women, ~2700kcal for men) for two days and, on the subsequent morning (subjects reported to the lab fasted) and after a thorough warm-up, have them perform
- 4 sets of 10 repetitions at 80% of their predetermined 1 RM, followed by another
- 4 sets of 15 repetitions at 65% of their 1 RM of single-legged leg presses.
- 150 mL of BCAAs (2:1:1 ratio) in flavored water, or
- 150 mL flavored water alone.
|Figure 1: Complete analysis of serum amino acid levels in the trained and untrained leg of subjects receiving BCAA or Placebo supplement before, during and after the completion of a standardized single-legged leg press exercise (data adapted from Borgenvik. 2011)|
|Figure 2: Relative increase / decrease in intra-muscular BCAAs and other EAAs in BCAA supplemented subjects vs. placebo control at different time-points before, during and after single-legged leg presses (data adapted from Borgenvik. 2011)|
pronounced reduction in the concentration of the aromatic amino acids, tyrosine and phenylalanine, in both plasma and muscle as well as muscle EAA (BCAA excluded) during the recovery periodBorgenik et al. observed in their study? The scientists at least conclude that
[s]ince tyrosine and phenylalanine are neither synthesized nor degraded in skeletal muscle, reduction in the levels of these amino acid could be indicative of an improved net muscle protein balance, i.e. an enhanced rate of synthesis and/or decreased rate of breakdown [and] could be explained by incorporation into protein.The accrual of muscle mass (whatever that may eventually mean, cf. yesterday's installment of the Intermittent Thoughts) thusly obviously relies on the presence of all essential amino acids and not just the "branched chained holy grail" of protein synthesis, of which the current study revealed that they (BCAA ingestion) reduced the expression of MAFbx, which regulates the protein transcription factor MyoD and the eukaryotic initiation factor-3f (eIF-3f), which, in turn is of importance in the mTOR-p70S6k signaling pathway, by 30% and 50% in the resting and exercising legs, respectively.
|Figure 3: Relative (compared to placebo) mTOR and p70S6K phosphorylation in response to BCAA supplementation in exercised (EX) and non-exercised (Rest) leg at different time-points before, and after single-legged leg presses (data adapted from Borgenvik. 2011)|
[...] tendency for BCAA supplementation to attenuate the elevation in the level of Rheb mRNA in both resting (1.7-fold under the placebo versus 1.2-fold in the BCAA condition) and exercising muscle (2.4-fold versus 1.5-fold).This ameliorative effect on Rheb, the low-molecular weight GTPase located immediately up-stream of mTOR, in combination with the exercise induced reductions in REDD2 expression (another negative regulator of mTOR) the scientists observed in the exercised leg are actually where we are currently at, as far as our understanding of the complex protein synthetic machinery goes. It is here at the gene-level where amino acid supplementation and its effect on Rheb and exercise and its effect on REDD synergize and facilitate those muscle gains trainees have been making for years often without any understanding of the biological underpinnings.
And though we may eventually be able to squeeze out another 5-10% more muscle mass, when we eventually get the "whole picture", I seriously doubt that even the most thorough understanding of the underlying biomolecular processes will change such basic recommendations as "take your 25g of fast digesting whey as a bolus immediately post workout" (cf. "Never Sip Your Whey!") - or what would you say?