Leucine-enriched amino acid ingestion after resistance exercise prolongs myofibrillar protein synthesis and amino acid transporter expression in older men.
Level 2 - randomized trial
Individual randomized controlled trial
PubMed 25332468 · doi:10.3945/jn.114.198671
What was done
Older men performed resistance exercise during a stable isotope infusion protocol (l-[ring-13C6]Phe and l-[1-13C]Leu). One hour after exercise, participants ingested 10 g of essential amino acids (EAAs) containing either a standard leucine dose matching quality protein (control, 1.85 g leucine, n = 7) or an enriched leucine dose (LEU, 3.5 g leucine, n = 8). Vastus lateralis muscle biopsies were obtained at rest and at 2, 5, and 24 hours post-exercise to measure myofibrillar protein synthesis (MyoPS), mTORC1 signaling, and amino acid transporter (AAT) mRNA expression.
What was found
p70 S6 kinase 1 phosphorylation increased in both groups at 2 h (P < 0.05), whereas 4E binding protein 1 phosphorylation increased only in the LEU group (P < 0.05). MyoPS increased similarly (~90% above basal) in both groups at 5 h (P < 0.05) and remained elevated (~90%) at 24 h only in the LEU group (P < 0.05). mRNA expression of select AATs was increased at 2 and 5 h in both groups (P < 0.05), but remained elevated at 24 h only in the LEU group (P < 0.05).
Why it matters
Leucine enrichment of post-exercise essential amino acids sustains myofibrillar protein synthesis and amino acid transporter expression for 24 hours in older men. This supports targeted nutritional strategies to help counter anabolic resistance in aging muscle.
Limits
The sample size was very small (n = 15 total) and restricted to older men. The study assessed only acute, 24-hour physiological responses to a single bout of exercise, rather than long-term gains in muscle mass, strength, or functional capacity.
Cited by
- supports Resistance training increases muscle uptake of leucine for up to 24 hours to stimulate muscle protein synthesis.