Leucine-enriched essential amino acid and carbohydrate ingestion following resistance exercise enhances mTOR signaling and protein synthesis in human muscle

Am J Physiol Endocrinol Metab. 2008 Feb;294(2):E392-400. doi: 10.1152/ajpendo.00582.2007. Epub 2007 Dec 4.


We recently showed that resistance exercise and ingestion of essential amino acids with carbohydrate (EAA+CHO) can independently stimulate mammalian target of rapamycin (mTOR) signaling and muscle protein synthesis in humans. Providing an EAA+CHO solution postexercise can further increase muscle protein synthesis. Therefore, we hypothesized that enhanced mTOR signaling might be responsible for the greater muscle protein synthesis when leucine-enriched EAA+CHOs are ingested during postexercise recovery. Sixteen male subjects were randomized to one of two groups (control or EAA+CHO). The EAA+CHO group ingested the nutrient solution 1 h after resistance exercise. mTOR signaling was assessed by immunoblotting from repeated muscle biopsy samples. Mixed muscle fractional synthetic rate (FSR) was measured using stable isotope techniques. Muscle protein synthesis and 4E-BP1 phosphorylation during exercise were significantly reduced (P < 0.05). Postexercise FSR was elevated above baseline in both groups at 1 h but was even further elevated in the EAA+CHO group at 2 h postexercise (P < 0.05). Increased FSR was associated with enhanced phosphorylation of mTOR and S6K1 (P < 0.05). Akt phosphorylation was elevated at 1 h and returned to baseline by 2 h in the control group, but it remained elevated in the EAA+CHO group (P < 0.05). 4E-BP1 phosphorylation returned to baseline during recovery in control but became elevated when EAA+CHO was ingested (P < 0.05). eEF2 phosphorylation decreased at 1 and 2 h postexercise to a similar extent in both groups (P < 0.05). Our data suggest that enhanced activation of the mTOR signaling pathway is playing a role in the greater synthesis of muscle proteins when resistance exercise is followed by EAA+CHO ingestion.

Publication types

  • Randomized Controlled Trial
  • Research Support, N.I.H., Extramural

MeSH terms

  • Absorptiometry, Photon
  • Adult
  • Amino Acids, Essential / pharmacology*
  • Blotting, Western
  • Cross-Sectional Studies
  • Dietary Carbohydrates / pharmacology*
  • Electrophoresis, Polyacrylamide Gel
  • Exercise / physiology*
  • Glucose / metabolism
  • Humans
  • Lactic Acid / metabolism
  • Leucine / pharmacology*
  • Male
  • Muscle Proteins / biosynthesis*
  • Muscle, Skeletal / drug effects
  • Muscle, Skeletal / metabolism*
  • Oncogene Protein v-akt / biosynthesis
  • Phenylalanine / metabolism
  • Physical Fitness / physiology
  • Protein Kinases / physiology*
  • Regional Blood Flow / physiology
  • Ribosomal Protein S6 Kinases / biosynthesis
  • Ribosomal Protein S6 Kinases / genetics
  • Signal Transduction / drug effects*
  • TOR Serine-Threonine Kinases
  • Tuberous Sclerosis Complex 2 Protein
  • Tumor Suppressor Proteins / biosynthesis
  • Tumor Suppressor Proteins / genetics


  • Amino Acids, Essential
  • Dietary Carbohydrates
  • Muscle Proteins
  • Tuberous Sclerosis Complex 2 Protein
  • Tumor Suppressor Proteins
  • Lactic Acid
  • Phenylalanine
  • Protein Kinases
  • MTOR protein, human
  • Oncogene Protein v-akt
  • Ribosomal Protein S6 Kinases
  • TOR Serine-Threonine Kinases
  • Leucine
  • Glucose