Strength
L-Leucine
L-Leucine is a BCAA that helps signal muscle protein synthesis but needs other essential amino acids.
How it counts: Not part of the score
We show it on the label and count it as disclosed, but it never affects Dose, any sub-score or the grade. The basis below explains why.
- Clinical dose
- No established clinical dose
- Safety ceiling
- —
- Evidence
- weak
- Category
- Strength
Evidence summary
Research confidence: low
No pre-workout reference dose. Leucine is one of the three branched-chain amino acids (BCAAs) and the main 'on switch' for muscle building, but muscle needs all nine essential amino acids to build protein; complete protein (or an essential amino acid blend) supplies them, BCAAs alone do not. BCAAs alone after lifting raised muscle building about half as much as whey protein did (Jackman 2017), and no study shows BCAAs taken before a workout improve that session. The 3 g in Pre JYM matches the top of the 0.7-3 g leucine per serving recommended within a complete protein dose (ISSN 2017).
Research sources
- Branched-chain amino acids and muscle protein synthesis in humans: myth or reality? (Wolfe, J Int Soc Sports Nutr 2017)(opens in new window)
- International Society of Sports Nutrition Position Stand: protein and exercise (Jäger et al., J Int Soc Sports Nutr 2017)(opens in new window)
Protein doses should contain 700-3000 mg leucine in addition to a balanced array of the essential amino acids; whole-food protein with all EAAs is preferred
- Branched-Chain Amino Acid Ingestion Stimulates Muscle Myofibrillar Protein Synthesis following Resistance Exercise in Humans (Jackman et al., Front Physiol 2017)(opens in new window)
10 trained men, 5.6 g BCAAs after resistance exercise: muscle protein synthesis 22% above placebo, about half the response the authors previously measured with 20 g whey carrying similar BCAAs. Funded by a GlaxoSmithKline research grant (GSK also supplied the drinks).