The Effect of Leucine-Enriched Essential Amino Acid Supplementation on Anabolic and Catabolic Signaling in Human Skeletal Muscle after Acute Resistance Exercise: A Randomized, Double-Blind, Placebo-Controlled, Parallel-Group Comparison Trial.
Level 2 - randomized trial
Individual randomized, double-blind, placebo-controlled parallel-group trial in humans
PubMed 32806711 · doi:10.3390/nu12082421
What was done
A randomized, double-blind, placebo-controlled, parallel-group comparison trial investigated the effect of leucine-enriched essential amino acid (LEAA) supplementation on anabolic, catabolic, and inflammatory signaling after acute resistance exercise. Twenty healthy young male subjects received either 5 g of LEAA or placebo and performed 3 sets of 10 repetitions of leg extensions and leg curls at 70% 1-repetition maximum. Muscle biopsy markers of mechanistic target of rapamycin complex 1 (mTORC1) signaling, the ubiquitin-proteasome system (MuRF-1, Atrogin-1, ubiquitinated proteins), and inflammatory cytokines (IL-1β, IL-6 mRNA) were measured.
What was found
LEAA supplementation significantly augmented post-exercise phosphorylation compared to placebo: - mTOR Ser2448: +77.1% (p < 0.05) - p70S6K Thr389: +1067.4% (p < 0.05) - rpS6 Ser240/244: +171.3% (p < 0.05) - 4EBP1 Thr37/46: +33.4% (p < 0.05) LEAA supplementation did not change ubiquitinated proteins, MuRF-1, or Atrogin-1 expression, nor did it alter IL-1β or IL-6 mRNA expression.
Why it matters
This study shows that a 5 g dose of LEAA augments acute post-exercise mTORC1 signaling in young men, though it does not modulate acute catabolic or inflammatory gene expression.
Limits
The sample size was small (n = 20 across two parallel groups). The study was restricted to healthy young men, limiting generalizability to females and older populations. Only acute molecular signaling was measured following a single bout of exercise, not direct muscle protein synthesis rates or long-term muscle hypertrophy.
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