Protein-leucine fed dose effects on muscle protein synthesis after endurance exercise

Med Sci Sports Exerc. 2015 Mar;47(3):547-55. doi: 10.1249/MSS.0000000000000447.

Abstract

Protein-leucine ingestion after strenuous endurance exercise accentuates muscle protein synthesis and improves recovery of muscle performance.

Purpose: The objective of this study is to determine whether a low-dose protein-leucine blend ingested after endurance exercise enhances skeletal muscle myofibrillar protein fractional synthetic rate (FSR).

Method: In a crossover design, 12 trained men completed 100 min of high-intensity cycling, then ingested either 70/15/180/30 g of protein/leucine/carbohydrate/fat (15LEU), 23/5/180/30 g of 5LEU, or 0/0/274/30 g of CON beverages in randomized order in four servings during the first 90 min of a 240-min recovery period. Muscle biopsies were collected at 30 and 240 min into recovery with FSR determined by L-[ring-13C6]phenylalanine incorporation and mTORC1 pathway phosphorylation by Western blot.

Results: The 33% (90% CL, ±12%) increase in FSR with 5LEU (mean, SD: 0.080, 0.014%·h(-1)) versus CON (0.060, 0.012%·h(-1)) represented near-maximal FSR stimulation. Tripling protein-leucine dose (15LEU: 0.090, 0.11%·h(-1)) negligibly increased FSR (13%, ±12% vs 5LEU). Despite similar FSR, mTORC1(Ser2448) phosphorylation only increased with 15LEU at 30 min, whereas p70S6K(Thr389), rpS6(Ser240/244), and 4E-BP1γ(Ser112) phosphorylation increased with protein-leucine quantity at one or both time points. Plasma leucine and essential amino acid concentrations decreased during recovery in CON but increased with protein-leucine dose. Serum insulin was increased in 15LEU versus CON (60%, ±20%) but was unaffected relative to 5LEU. Regression analysis revealed p70S6K-rpS6 phosphorylation moderately predicted FSR, but the associations with plasma leucine and essential amino acids were small.

Conclusions: Ingesting 23 g of protein with 5 g of added leucine achieved near-maximal FSR after endurance exercise, an effect unlikely attributable to mTORC1-S6K-rpS6 signaling, insulin, or amino acids. Translating the effects of protein-leucine quantity on protein synthesis to optimizing adaptation and performance requires further research.

Publication types

  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Amino Acids, Essential / blood
  • Beverages
  • Blood Glucose / metabolism
  • Cross-Over Studies
  • Dietary Carbohydrates / administration & dosage
  • Dietary Fats / administration & dosage
  • Dietary Proteins / administration & dosage*
  • Dietary Proteins / metabolism
  • Humans
  • Insulin / blood
  • Leucine / administration & dosage*
  • Leucine / blood
  • Male
  • Mechanistic Target of Rapamycin Complex 1
  • Multiprotein Complexes / metabolism
  • Muscle Proteins / biosynthesis*
  • Muscle, Skeletal / metabolism
  • Myofibrils / metabolism
  • Physical Endurance / physiology*
  • Single-Blind Method
  • TOR Serine-Threonine Kinases / metabolism

Substances

  • Amino Acids, Essential
  • Blood Glucose
  • Dietary Carbohydrates
  • Dietary Fats
  • Dietary Proteins
  • Insulin
  • Multiprotein Complexes
  • Muscle Proteins
  • TOR Serine-Threonine Kinases
  • Mechanistic Target of Rapamycin Complex 1
  • Leucine