Interessant
Ekstra tilførsel av leucin til en allerede balansert aminosyreprofil har ikke vist seg ha noen ekstra effekt:
1. "We conclude that increasing the proportion of leucine in a mixture of EAA can reverse an attenuated response of muscle protein synthesis in elderly but does not result in further stimulation of muscle protein synthesis in young subjects. "
Am J Physiol Endocrinol Metab 291: E381-E387, 2006.
2. "Co-ingestion of leucine with carbohydrate and protein following physical activity does not further elevate muscle protein fractional synthetic rate in elderly men when ample protein is ingested."
British Journal of Nutrition (2008), 99:571-580Veeeeeeeeeel...
Leucine and the Modulation of Insulin Release
As many know, the release of insulin has been correlated with many anabolic properties involved with tissue building. Insulin has been proven to stimulate protein synthesis and inhibit protein breakdown when administered both during and post-exercise (Manninen et al, 2006).
Interestingly, in an investigation by Manninen in 2006 involving the supplementation of a carbohydrate, protein hydrolysate, and leucine mixture taken during exercise, it was demonstrated that this mixture leads to greater increases in skeletal muscle hypertrophy and strength vs. a placebo supplement.
It was once believed that insulin secretion was controlled almost entirely by blood glucose concentration. It's since become apparent that amino acids play a crucial role in the regulation of insulin secretion. Certain amino acids have been shown to cause insulin release in humans, even under conditions where blood sugar levels are normal (Manninen et al, 2006).
Of course, in order for most amino acids to effectively stimulate pancreatic beta cell insulin release, permissive levels of blood glucose (2.5 — 5.0 mM) must be present. Interestingly, leucine is an exception, as it's the only amino acid capable of increasing circulating insulin levels regardless of blood glucose concentration (Manninen et al, 2006). The increase of insulin has been shown to decrease the rate of muscle protein degradation.
By limiting protein degradation, leucine may allow for a net protein synthesis post-resistance exercise, leading to greater muscle hypertrophy. Essentially, this insulin response will provide an environment that promotes tissue building, as opposed to tissue breakdown.
Yet here's an important question: if an insulin release produces muscle growth, why wouldn't you simply drink a carbohydrate solution to get this insulin response?
In a study examining plasma insulin release, a 221% greater insulin response was achieved when subjects ingested a high glycemic carbohydrate bolus with protein hydrolysate and leucine as opposed to carbohydrate alone. When the subjects ingested carbohydrate with protein hydrolysate, but without leucine, a 66% greater insulin response was observed than with carbohydrate alone (Manninen et al, 2006).
Based on these results, it's evident that leucine supplementation is beneficial to resistance exercise in terms of its ability to modulate insulin signaling. Post-exercise hyperinsulinaemia (high insulin) supported by hyperaminoacidaemia (high amino acids) induced by protein hydrolysate and leucine ingestion increases net protein deposition in muscle, leading to increased skeletal muscle hypertrophy and strength (Manninen et al, 2006).
So, the bottom line is this: during and post-exercise, it's ideal to ingest a fast-digesting drink of hydrolyzed protein, sugary carbs, and some additional BCAA (especially leucine) because of the combined high blood insulin and high blood amino acid concentrations that accompany such a beverage.
However, based on the research, this type of drink doesn't only work through the modulation of insulin release. Leucine helps grow muscle because it's also a key element in the activation of translational pathways responsible for muscle growth.
Leucine and the Initiation of Translation
Translation, as a review, is the synthesis of protein as directed by mRNA (messenger RNA). It's the first of three stages in protein synthesis, with the other two stages being chain elongation and termination (Norton.et al, 2006). Without translation, there can't be protein synthesis or muscle growth.
Previously, the effects of resistance exercise in relation to protein balance were discussed. It was determined that after exhaustive resistance training, the body is in a catabolic state until nutrition is provided, activating the recovery phase. During this catabolic state, muscle protein synthesis becomes impaired (at the cellular level) due to the inhibition of specific translation initiation factors.
These factors — eIF4G, eIF4E and rpS6 specifically — are what turn on the process of translation and eventually, protein synthesis. And they're controlled by, you guessed it, intracellular insulin signalling and leucine concentrations (Norton.et al, 2006). Therefore, the anabolic effect of exercise and nutrition is likely mediated by activating signal transduction of these initiating factors.
It's been revealed that activation of this translational pathway (displayed below; Layman et al, 2006) is crucial for skeletal muscle recovery and hypertrophy.
As you can see, leucine is necessary for the activation of certain initiation factors. When leucine is ingested, tissue levels increase. This means the inhibition of the above mentioned initiation factors is released. This happens through activation of the protein kinase mammalian target of rapamycin (mTOR above).
Leucine's effect on mTOR is also synergistic with insulin via the phosphoinositol 3-kinase signaling pathway (PI3 above; Norton.et al, 2006). Together, insulin and leucine allow skeletal muscle to coordinate protein synthesis. The figure below provides evidence supporting the above hypothesis.
In the figure above (Blomstrand et al, 2006), BCAA supplementation consumed post-resistance exercise had a significant effect on translation initiating factors p70S6 kinase and mTOR. The role of leucine and other BCAA is to phosphorylate the proteins serine and threonine, which in turn will produce a phosphorylating cascade eventually initiating the translation of protein synthesis.
The fundamental idea to take away is that BCAA, in particularly leucine, reverse the inhibition of translation produced by resistance training. In reversing this inhibition, BCAA will allow for increased muscle hypertrophy through greater levels of protein synthesis.
At this point, you might be wondering why supplemental leucine is necessary when skeletal muscles are already comprised of one-third BCAA. Well, during resistance training, BCAA oxidation in skeletal muscle increases through activation of the branched-chain a-keto acid dehydrogenase (BCKDH).
This means that plasma and intracellular concentrations of leucine decrease. Consequently, the ability of leucine to stimulate insulin release and initiate translation will be diminished until during or post-exercise supplementation is provided.
BCAA, Resistance Training, and Protein Synthesis — What's The Verdict?
So, in the end, the question to ask is this: is leucine supplementation an ergogenic aid in terms of resistance training?
Based on the current literature and the information provided above, the answer is yes. Leucine can act as an ergogenic aid for resistance training athletes based on its ability to modulate insulin signaling and initiate translation of protein synthesis. Both of these factors contribute to greater skeletal muscle hypertrophy and strength."