L-Leucine is 1 of 3 branched-chain amino acids (BCAA) and is credited by researchers as a main cause of benefits associated with BCAA supplementation.
The “L” in front of leucine –or any other amino acid –stands for “levo,” denoting the spiral rotation of the chemical structure.
L-leucine, like the other BCAAs isoleucine and valine, is an essential amino acid and differs from other amino acids because it is mostly oxidized in skeletal muscle. Consequently, L-leucine is more readily available.
Leucine’s oxidation rate is highest of the BCAAs.
While BCAAs combined are clinically proven to provide ergogenic and exercise-recovery advantages, researchers are becoming more interested in l-leucine when supplemented by itself, as its benefits tend to surpass its BCAA counterparts’.
Research shows L-leucine plays an imperative role in muscle metabolism and exercise performance.
L-Leucine boosts muscle protein synthesis and combats protein degradation by activating a protein complex mTOR, short for mammalian target of rapamycin.
In one study, researchers administered 2 amino acid drinks containing 3.5 and 1.87 g leucine to test subjects who underwent steady-state exercise. Results show muscle protein synthesis was 33% greater after ingesting the 3.5 g leucine dose.
Leucine’s effects are said to be “at least in part, associated with the absence of branched-chain aminotransferase (BCAT) enzyme in the liver.”
Enhanced strength performance is a benefit associated with daily l-leucine supplementation.
During a 12-week resistance-training program, 26 men supplemented with leucine or a placebo and trained 2 times a week. Test subjects underwent a 5 repetition maximum (5-RM) exercise to measure strength output.
Results show those who ingested leucine experienced “higher gains in total 5-RM strength (sum of 5-RM in eight exercises) and 5-RM strength in five out of the eight exercises.” These observations lead researchers to conclude l-leucine supplementation might be useful in increasing strength performance.
There are no reported side effects associated with l-leucine supplementation on its own. An online medical authority indicates BCAAs are generally safe when used for up to 6 months but may result in fatigue and loss of coordination.
In clinical studies, l-leucine is usually accompanied alongside isoleucine and valine. A common BCAA ratio found in several sports supplements is 2:1:1, meaning 2 parts leucine to 1 part isoleucine and valine.
In one study, an amino acid drink mixture containing 3.5 g l-leucine was used to study muscle protein synthesis.
A 4 g l-leucine dose was studied during a study analyzing strength performance.
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