Muscle protein breakdown has a minor role in the protein anabolic response to essential amino acid and carbohydrate intake following resistance exercise

Am J Physiol Regul Integr Comp Physiol. 2010 Aug;299(2):R533-40. doi: 10.1152/ajpregu.00077.2010. Epub 2010 Jun 2.


Muscle protein breakdown (MPB) is increased following resistance exercise, but ingestion of carbohydrate during postexercise recovery can decrease MPB with no effect on muscle protein synthesis (MPS). We sought to determine whether a combination of essential amino acids (EAA) with low carbohydrate or high carbohydrate could effectively reduce MPB following resistance exercise and improve muscle protein net balance (NB). We hypothesized that higher levels of carbohydrate and resulting increases in circulating insulin would inhibit MPB and associated signaling, resulting in augmented NB. Thirteen male subjects were assigned to one of two groups receiving equivalent amounts of EAA (approximately 20 g) but differing carbohydrate levels (low = 30, high = 90 g). Groups ingested nutrients 1 h after an acute bout of leg resistance exercise. Leg phenylalanine kinetics (e.g., MPB, MPS, NB), signaling proteins, and mRNA expression were assessed on successive muscle biopsies using stable isotopic techniques, immunoblotting, and real-time quantitative PCR, respectively. MPB tended to decrease (P < 0.1) and MPS increased (P < 0.05) similarly in both groups following nutrient ingestion. No group differences were observed, but muscle ring finger 1 (MuRF1) protein content and MuRF1 mRNA expression increased following resistance exercise and remained elevated following nutrient ingestion, while autophagy marker (light-chain 3B-II) decreased after nutrient ingestion (P < 0.05). Forkhead box-O3a phosphorylation, total muscle atrophy F-box (MAFbx) protein, and MAFbx and caspase-3 mRNA expression were unchanged. We conclude that the enhanced muscle protein anabolic response detected when EAA+carbohydrate are ingested postresistance exercise is primarily due to an increase in MPS with minor changes in MPB, regardless of carbohydrate dose or circulating insulin level.

Publication types

  • Clinical Trial
  • Research Support, N.I.H., Extramural

MeSH terms

  • Adult
  • Amino Acids, Essential / administration & dosage*
  • Biopsy
  • Blood Glucose / metabolism
  • Caspase 3 / metabolism
  • Cross-Sectional Studies
  • Dietary Carbohydrates / administration & dosage*
  • Dietary Carbohydrates / blood
  • Dietary Proteins / administration & dosage*
  • Dietary Proteins / blood
  • Dietary Proteins / pharmacokinetics
  • Forkhead Box Protein O3
  • Forkhead Transcription Factors / metabolism
  • Gene Expression Regulation
  • Humans
  • Insulin / blood
  • Male
  • Microtubule-Associated Proteins / metabolism
  • Muscle Contraction*
  • Muscle Proteins / genetics
  • Muscle Proteins / metabolism*
  • Muscle, Skeletal / metabolism*
  • Phosphorylation
  • Postprandial Period
  • RNA, Messenger / metabolism
  • Resistance Training*
  • SKP Cullin F-Box Protein Ligases / metabolism
  • Signal Transduction
  • Tripartite Motif Proteins
  • Ubiquitin-Protein Ligases / metabolism


  • Amino Acids, Essential
  • Blood Glucose
  • Dietary Carbohydrates
  • Dietary Proteins
  • FOXO3 protein, human
  • Forkhead Box Protein O3
  • Forkhead Transcription Factors
  • Insulin
  • MAP1LC3B protein, human
  • Microtubule-Associated Proteins
  • Muscle Proteins
  • RNA, Messenger
  • Tripartite Motif Proteins
  • FBXO32 protein, human
  • SKP Cullin F-Box Protein Ligases
  • TRIM63 protein, human
  • Ubiquitin-Protein Ligases
  • CASP3 protein, human
  • Caspase 3